nmap/docs/scripting.xml

<sect1 id="nse-intro">
    <title>Introduction</title>

    <indexterm><primary>Nmap Scripting Engine</primary></indexterm>
    <para>The Nmap Scripting Engine (NSE) is one of Nmap's most
    powerful and flexible features.  It allows users to write (and
    share) simple scripts to automate a wide variety of networking
    tasks.  Those scripts are then executed in parallel with the speed
    and efficiency you expect from Nmap.  Users can rely on the
    growing and diverse set of scripts distributed with Nmap, or write
    their own to meet custom needs.</para>

    <para>The Nmap project would like to thank Diman Todorov for
    his excellent work building the initial NSE implementation and
    writing much of this documentation.  Stoiko Ivanov also
    contributed greatly.  The tasks we had in mind when
    creating the system are:</para>    

    <variablelist>
      <varlistentry>
        <term>Network discovery</term>
        <listitem>
          <para>This is Nmap's bread and butter. Examples include
           looking up whois data based on the target domain,
           querying ARIN, RIPE, or APNIC for the target IP to determine ownership,
           performing identd lookups on open ports, SNMP queries, and
           listing available NFS/SMB/RPC shares and services.</para>
        </listitem>

      </varlistentry>
      <varlistentry>
        <term>More sophisticated version detection</term>
        <listitem>
          <para>The Nmap version detection system (<xref linkend="vscan"/>)
       is able to recognize thousands of different services through
       its probe and regular expression based matching system, but it
       cannot recognize everything.  For example, identifying the Skype v2 service requires two
       independent probes.  Nmap could also recognize more SNMP services
       if it tried a few hundred different community names by brute
       force.  Neither of these tasks are well suited to traditional
       Nmap version detection, but both are easily accomplished with
       NSE.  For these reasons, version detection now calls NSE by
       default to handle some tricky services.  This is described in
       <xref linkend="nse-vscan"/>.</para>

        </listitem>
      </varlistentry>
      <varlistentry>
        <term>Vulnerability detection</term>
        <listitem>

          <para>When a new vulnerability is discovered, you often want
       to scan your networks quickly to identify vulnerable systems
       before the bad guys do.  While Nmap isn't a
       comprehensive 
<web>
<ulink url="http://sectools.org/vuln-scanners.html">vulnerability scanner</ulink>,
</web><print>
vulnerability scanner,
</print>

       we plan to distribute scripts for some very severe or common vulnerabilities and misconfigurations.</para>

        </listitem>
      </varlistentry>
      <varlistentry>
        <term>Backdoor detection</term>
        <listitem>
          <para>
	   Many attackers and some automated worms leave
	   backdoors to enable later reentry.  Some of these can be
	   detected by Nmap's regular expression based version detection.
	   For example, within hours of the MyDoom worm hitting the
	   Internet, Jay Moran posted an Nmap version detection probe and
	   signature so that others could quickly scan their networks.
	   For more complex worms and backdoors, NSE is needed
	   instead.
       </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>Vulnerability exploitation</term>
        <listitem>
          <para>
	   As a general scripting language, NSE could even
	   be used to exploit vulnerabilities rather than just find them.
	   The capability to add custom exploit scripts may be valuable
	   for some people (particularly penetration testers), though we aren't
	   planning to turn Nmap into an exploitation framework like
	   <ulink url="http://www.metasploit.com">Metasploit</ulink>.
       </para>
        </listitem>
      </varlistentry>
    </variablelist>
    <para>
      The listed items are just the initial script classes.  It is
      likely that Nmap users will come up with even more inventive
      uses for NSE.
    </para>


    <para>
      Scripts are written in the
      embedded <ulink url="http://www.lua.org/">Lua programming language</ulink>.  
      The language itself is well documented in the books 
      <citetitle><ulink url="http://www.amazon.com/exec/obidos/ASIN/8590379825/secbks-20">Programming
	in Lua, Second Edition</ulink></citetitle> and
      <citetitle><ulink url="http://www.amazon.com/exec/obidos/ASIN/8590379825/secbks-20">Lua
	5.1 Reference Manual</ulink></citetitle>.  The reference manual is also 
      <ulink url="http://www.lua.org/manual/5.1/">freely available
	online</ulink>, as is the 
      <ulink url="http://www.lua.org/pil/">first edition of Programming in
	Lua</ulink>. Given the availability of these excellent general
      Lua programming references, this document only covers aspects and
      extensions specific to the Nmap implementation.
    </para>
    <para>

      NSE is activated with the <option>-sC</option> option (or
      <option>--script</option> if you wish to specify a custom set of
      scripts) and results are integrated into Nmap normal and XML
      output.  Two types of scripts are supported: service and host
      scripts.  Service scripts relate to a certain open port
      (service) on the target host, and any results they produce are included
      next to that port in the Nmap output port table.  Host scripts,
      on the other hand, run no more than once against each target IP
      and produce results below the port table.  <xref
      linkend="nse-ex1"/> shows a typical script scan.  Examples of
      service scripts producing output are <literal>Stealth SSH
      Version</literal>, which tricks some SSH servers into divulging
      version information without logging the attempt as they normally
      would, <literal>Service Owner</literal>, which connects to open
      ports, then performs a reverse-identd query to determine what
      username it is running under, and <literal>HTML Title</literal>,
      which simply grabs the title of the root path of any web servers
      found.  A sample host script is <literal>RIPE Query</literal>,
      which looks up and reports target IP ownership information.

    </para>
    <example id="nse-ex1">
      <title>Typical NSE Output</title>
<screen>
$ ./nmap -sC localhost -p 22,23,80,113

Starting Nmap 4.20ALPHA9-NSE ( http://insecure.org )
Interesting ports on localhost (127.0.0.1):
PORT    STATE  SERVICE
22/tcp  open   ssh
|_ Stealth SSH version: SSH-1.99-OpenSSH_4.2
|_ SSH protocol version 1: Server supports SSHv1
23/tcp  closed telnet
80/tcp  open   http
|_ HTML title:Test Page for Apache Installation
113/tcp closed auth

Host script results:
|_ RIPE Query: IP belongs to:          Internet Assigned Numbers Authority

Nmap finished: 1 IP address (1 host up) scanned in 0.907 seconds
</screen>
    </example>

  </sect1>
  <sect1 id="nse-usage">
    <title>Usage and Examples</title>
    <para>
      While NSE has a complex implementation for efficiency, it is
      strikingly easy to use.  Simply specify <option>-sC</option> to
      enable the most common scripts.  Or specify the
      <option>--script</option> option to choose your own scripts to
      execute by providing categories, script file names, or the name of
      directories full of scripts you wish to execute.  You can customize 
	  some scripts by providing arguments to them via the
	  <option>--script-args</option> option. The two
      remaining options, <option>--script-trace</option> and
      <option>--script-updatedb</option>, are generally only used for
      script debugging and development.
    </para>

    <sect2 id="nse-categories"><title>Script Categories</title>

    <para>NSE scripts define a list of categories they belong to.
          Currently defined categories are <literal>safe</literal>,
          <literal>intrusive</literal>, <literal>malware</literal>,
          <literal>version</literal>, <literal>discovery</literal> and
          <literal>vulnerability</literal>.  By default, Nmap runs all
          scripts in either the <literal>safe</literal> or
          <literal>intrusive</literal> categories.  Categories are not
          case sensitive.  The following list describes each category.</para>

     <variablelist>
        <varlistentry>
          <term>
            <option>safe</option>
          </term>
          <listitem>
            <para>Scripts
	      which weren't designed to crash services, use large
	      amounts of network bandwidth or other resources, or
	      exploit security holes. These are less likely to offend
	      remote sysadmins.  Of course (as with all other Nmap
	      features) we cannot guarantee that they won't ever cause
	      adverse reactions.  Most of these perform general
	      network discovery. Examples are echoTest (sends a string
	      to the UDP echo service) and showHTMLTitle (grabs the
	      title from a web page).</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term>
            <option>intrusive</option>
          </term>
          <listitem>
            <para>These are not intended to
              crash or damage anything, but are more likely to leave
              suspicious logs or otherwise arouse sysadmin ire. Scripts
              which attempt to login to services with default passwords
              fall into this class.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term>
            <option>malware</option>
          </term>
          <listitem>
            <para>These scripts test if the target platform is
            infected by malware or backdoors.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term>
            <option>version</option>
          </term>
          <listitem>
            <para>This category cannot be selected explicitly. It is only 
		    run if <option>-sV</option>
	        was supplied. The scripts in this category are an
	        extension to the version detection service. Their output
	        cannot be distinguished from version detection output
	        and they do not produce script scanning
	        output. </para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term>
            <option>discovery</option>
          </term>
          <listitem>
            <para>These scripts try to actively learn more about the
            network by querying public registries, SNMP-enabled
            devices, directory services, and the like.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term>
            <option>vulnerability</option>
          </term>
          <listitem>
            <para>These scripts check for a specific vulnerability and report results only if it is found.</para>
          </listitem>
        </varlistentry>
    </variablelist>

    </sect2>
	<sect2 id="nse-args">
      <title>Arguments to Scripts</title>
      <para>
      You can pass arguments to NSE scripts via the
	  <option>--script-args</option> option. The script-arguments generally are
	  name-value pairs, which are provided to the script as a Lua table called
	  <literal>args</literal> inside the <literal><link
	  linkend="nse-api-registry">nmap.registry</link></literal> with
	  the names as keys for the corresponding values. The values can either be
	  strings or tables. Subtables can be used to pass arguments to 
	  scripts with a finer granularity (e.g. pass different usernames for
	  different scripts). A typical nmap invocation with script arguments may
	  look like:
	  </para>
	  <para>
<userinput>
$ nmap -sC --script-args user=foo,pass=bar,anonFTP={pass=ftp@foobar.com}
</userinput>
	  </para>
	  <para>
	  which would result in the Lua table: 
          </para>
<programlisting>
{user="foo",pass="bar",anonFTP={pass=nobody@foobar.com}}
</programlisting>
 
	  <para>You could therefore access the username (<literal>"foo"</literal>)
	  inside your script as <literal>local username= nmap.registry.args.user
	  </literal>. As a general rule the subtables used to override
	  options for scripts should be named as the script's
	  <literal>id</literal>, since otherwise scripts can't know where to
	  search for their arguments.
	  </para>
	</sect2>

    <sect2 id="nse-cmd-line-args">
      <title>Command-line Arguments</title>
      <para>
	These are the five command line arguments specific to script-scanning:
      </para>
      <variablelist>
        <varlistentry>
          <term>
            <option>-sC</option>
            <indexterm>
              <primary>-sC</primary>
            </indexterm>
          </term>
          <listitem>
            <para>Performs a script scan using the default set of scripts. It is
              equivalent to
              <option>--script=safe,intrusive</option>.</para>
          </listitem>
        </varlistentry>

     <varlistentry>
        <term><option>--script &lt;script-categories|directory|filename|all&gt;</option><indexterm><primary>--script</primary></indexterm></term>

<listitem>
<para>Runs a script scan (like <option>-sC</option>) with the scripts you have chosen rather than the defaults.  Arguments can be script categories, single scripts or directories with scripts which are to be run against the target hosts instead of the default set. Nmap will try to interpret the arguments at first as categories and afterwards as files or directories.  Absolute paths are used as is, relative paths are searched in the following places until found:
<filename>--datadir/</filename>; 
<filename>$(NMAPDIR)/</filename>; 
<filename>~user/nmap/</filename> (not searched on Windows); 
<filename>NMAPDATADIR/</filename> or  
<filename>./</filename>.  A <filename>scripts/</filename> subdirectory is also tried in each of these.  Give the argument <literal>all</literal> to execute all scripts in the Nmap script database.
</para>

<para>If a directory is specified and found, Nmap loads all NSE
scripts (any filenames ending with <literal>.nse</literal>) from that
directory.  They must have the filename extension
<literal>nse</literal>.  Nmap does not recurse into subdirectories to
find scripts.  When individual file names are specified, the file
extension does not have to be <literal>nse</literal>.
</para>

<para>Nmap scripts are stored in a <filename>scripts</filename>
subdirectory of the Nmap data directory
<bookex>(see <xref linkend="data-files"/>)</bookex>
<notbook>(see the <ulink url="http://nmap.org/man/man-misc-options.html"><option>--datadir</option>
option</ulink>)</notbook>
by default.  Scripts are indexed in a database stored in
<filename>scripts/script.db</filename>. The database lists all of the
scripts in each category. A single script may be in several
categories.</para>

          </listitem>
        </varlistentry>

        <varlistentry>
          <term>
            <option>--script-args</option>
            <indexterm>
              <primary>--script-args</primary>
            </indexterm>
          </term>
          <listitem>
            <para>provides arguments to the scripts. See <xref
			linkend="nse-args"/> for a detailed explanation.</para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term>
            <option>--script-trace</option>
            <indexterm>
              <primary>--script-trace</primary>
            </indexterm>
          </term>
          <listitem>
            <para>

	      This option is similar to
              <option>--packet-trace</option>, but works at the
              application level rather than packet by packet. If this
              option is specified, all incoming and outgoing
              communication performed by scripts is printed. The
              displayed information includes the communication
              protocol, source and target addresses, and the
              transmitted data. If more than 5% of transmitted data is
              unprintable, hex dumps are given instead.

	    </para>
          </listitem>
        </varlistentry>
        <varlistentry>
          <term>
            <option>--script-updatedb</option>
            <indexterm>
              <primary>--script-updatedb</primary>
            </indexterm>
          </term>
          <listitem>
            <para>This option is only useful if you have added or
              removed NSE scripts from the default
              <literal>scripts</literal> directory, or if you have
              changed any of the scripts' <literal>categories</literal>
              fields.  This field contains categories such as
              <literal>safe</literal> and <literal>discovery</literal>
              which the script belongs to.  Categories may be
              specified with the <option>--script</option> option. For
              efficiency reasons, NSE generates a
              <filename>script.db</filename> file which maps
              categories to the scripts they contain. If you changed
              tag directives or added/removed scripts, run
              <command>nmap --script-updatedb</command>. 
	    </para>
          </listitem>
        </varlistentry>
      </variablelist>

      <para>
        Some of the Nmap options have effects on script scans. The most
        prominent of these is <option>-sV</option>. A version scan executes
        the scripts in the <literal>version</literal> category. The scripts
        in this category are slightly different than other scripts. Their
        output blends in with the version scan and they do not produce any
        script scan output.
      </para>
      <para>
        Another option which has effect on the scripting engine is 
	<option>-A</option>. The aggressive mode of Nmap implies
	the option <option>-sC</option>.
      </para>
      <para>
      </para>
    </sect2>
    <sect2 id="nse-usage-examples">
      <title>Usage Examples</title>
      <para> 
	Simple script scan.
      </para>
      <para>
        <userinput> 
	  $ nmap -sC hostname
      </userinput>
      </para>
      <para> 
	Tracing a specific script.
      </para>
      <para>
        <userinput> 
	  $ nmap --script=./showSSHVersion.nse --script-trace hostname
      </userinput>
      </para>
    </sect2>
  </sect1>
  <sect1 id="nse-scripts">
    <title>Script Format</title>
    <para>NSE scripts consist of four descriptive fields, a port or host rule defining when the script should be executed, and an action block containing the actual script instructions.  All six of these are Lua variables that are assigned to.  Their names must be lowercase as shown here.

    </para>
    <sect2 id="nse-format-id">
      <title><literal>id</literal> Field</title>
      <para>
	The script's <literal>id</literal> field is displayed in the Nmap output 
	table if the script produces any output.  It should be unique so users
	can identify exactly which script file produced a message. IDs
	should be kept short to conserve space in Nmap output, while
	still being meaningful enough for users to recognize.  Some
	good examples are <literal>RIPE query</literal>, <literal>HTML
	title</literal>, and <literal>Kibuv worm</literal>.
      </para>
    </sect2>
    <sect2 id="nse-format-description">
      <title><literal>description</literal> Field</title>
      <para>
	The description describes what the script is testing for and
	any critical notes the user must be aware of. A good example
	example is this user contributed recursive DNS script
	description <quote>Checks whether a nameserver on UDP port 53
	allows queries for third party names. It is expected that
	recursion will be enabled on your own internal
	nameserver.</quote>
      </para>
    </sect2>

    <sect2 id="nse-format-author">
      <title><literal>author</literal> Field </title>
      <para>
	The <literal>author</literal> field contains the script authors name and contact information. If you are worried about spam, you might want to omit or obscure your email address, or give your home page URL instead.  This optional field is not used by NSE, but is important for giving script authors due credit or blame. 
      </para>
    </sect2>

    <sect2 id="nse-format-license">
      <title><literal>license</literal> Field </title>
      <para>This field describes the license applied to the script.  All scripts currently shipped with Nmap contain:</para>
<programlisting>
license = "Same as Nmap--See http://nmap.org/man/man-legal.html"
</programlisting>
<para>See <xref linkend="nse-license"/> for further details on contributing NSE scripts to Nmap.
      </para>
    </sect2>

    <sect2 id="nse-format-runlevel">
      <title><literal>runlevel</literal> Field</title>
      <para>
	This optional field determines script execution order.  When
	this section is absent the run level defaults to 1.0. A script
	with the run level 1.0 is run before any scripts with <literal>runlevel</literal> set to
	<literal>2.5</literal>, which in turn runs before any scripts
	with <literal>runlevel 2.55</literal>.  No particular order
	is guaranteed for scripts with the same run level. One
	application of run levels is allowing scripts to depend on
	each other. If <literal>script A</literal> relies on some
	information gathered by <literal>script B</literal>, give
	<literal>B</literal> a lower run level than
	<literal>A</literal>. <literal>Script B</literal> can store
	information in the NSE registry for <literal>A</literal> to
	retrieve later. For information on the NSE registry see to
	<xref linkend="nse-api-registry"/>.
      </para>
    </sect2>

    <sect2 id="nse-format-rules">
      <title>Port and Host Rules</title>
      <para>

	There are two types of rules: <emphasis>host rules</emphasis>
	which run only once against a target IP and <emphasis>port
	rules</emphasis> which run against individual ports on a
	target.  A rule is a Lua function which takes a host and a
	port table as arguments and returns a boolean. If the rule
	evaluates to <literal>true</literal>, the script action 
	is performed. Otherwise the action is skipped. Port rules are
	only matched against TCP or UDP ports in the
	<literal>open</literal>, <literal>open|filtered</literal> or
	<literal>unfiltered</literal>
	states. Host rules are matched exactly once against every
	scanned host. The action, like the rule, is a Lua function,
	which takes a host and port table as arguments. If the script is
	matched using a host rule, then <literal>nil</literal> is passed instead of a port table.  Example rules are shown in
	<xref linkend="nse-tutorial-rule"/>.</para> </sect2>

     <sect2 id="nse-format-action"><title>Action</title>

      <para>
	The action is the heart of an NSE script.  It contains all of
	the instructions to be executed when the script's port or host
	rule triggers.  It is a Lua function which returns either
	<literal>nil</literal> or a string. If a string is returned,
	it is printed along with the script ID in (if it is a service
	script) or below (if it is a host script) the Nmap port table.
	If the script returns <literal>nil</literal>, no output is
	produced. All variables in the
	action and rule segments must be declared <literal>local</literal>.  For an
	example of an NSE action refer to <xref
	linkend="nse-tutorial-action"/>.
      </para>
    </sect2>

  </sect1>
  <sect1 id="nse-language">
    <title>Script Language</title>
    <para>
      Nmap's scripting engine consists of three more or less distinct
      parts. The largest part is the embeddable Lua interpreter. This
      is a lightweight language designed for extensibility.  It offers
      a powerful and well documented API for interfacing with other
      software (such as Nmap).
    </para>

    <para>
      The second part of the Nmap scripting engine is the NSE library, which
      connects Lua and Nmap. This layer
      handles issues such as initialization of the Lua interpreter, 
      scheduling of parallel script execution, script retrieval and
      more. It is also the heart of the NSE network I/O framework and the
	  exception handling mechanism.
    </para>

    <para>
    Lua was designed with a small feature set to ease embedding. So
    we have added extensions to support more specialized
    functionality.  These basically are 
	<ulink url="http://www.lua.org/manual/5.1/manual.html#5.3">Lua modules</ulink> written either in Lua itself, or where needed in C. This 
	NSE library is the third part of the NSE.
	</para>
    
	<sect2 id="nse-lua">
      <title>Lua Base Language</title>
      <para>

	The Nmap scripting language is an embedded <ulink
	url="http://www.lua.org/">Lua</ulink> interpreter which was
	extended with libraries for interfacing with Nmap.  The Nmap
	API is in the Lua namespace <literal>nmap</literal>.  This
	means that all calls to resources provided by Nmap have an
	<literal>nmap</literal> prefix.
	<literal>nmap.new_socket()</literal>, for example, returns a
	new socket wrapper object. The Nmap library layer also takes
	care of initializing the Lua context, scheduling parallel
	scripts and collecting the output produced by completed
	scripts.  
	</para>
      <para>

	During the planning stages, we considered several programming
	languages as the bases for Nmap scripting. One option was to
	implement a completely new programming language. The criteria
	imposed on the options were strict, NSE needed to be easy to
	use, small in size, compatible with the Nmap license,
	scalable, fast and parallelizable.  There have been several
	efforts to design a security auditing language from scratch
	which have resulted in well known awkward solutions. It was
	clear from the beginning that we would not go down this
	road. For a while the Guile scheme interpreter was considered
	but the preference drifted towards Elk in favor of its more
	liberal license. But parallelizing Elk scripts would have been
	difficult. In addition, the subset of Nmap users familiar with
	functional programming is regarded too small to consider
	Scheme as an option.  Larger interpreters like Perl, Python or
	Ruby are well known and loved, but are difficult to embed
	efficiently.  In the end, Lua exceeded in all criteria for
	NSE. It is small, distributed under the MIT license, has
	coroutines which provide a sane method for parallel script
	execution, was designed with embeddability in mind, has
	excellent documentation, and is actively developed by a large
	and committed community.

      </para>
    </sect2>
	</sect1>
    <sect1 id="nse-library">
      <title>Lua Extensions</title>
      <para>In addition to the significant built-in capabilities of
      Lua, we have written or integrated several extensions to make
      NSE scripts more powerful and convenient to write. These 
	  <emphasis>modules</emphasis> are compiled and installed along with 
	  Nmap. They have their own directory, <filename>nselib</filename>, which
	  is installed in the configured datadir. Scripts need only <literal>require</literal> the default modules in order to use them.  The default modules are described in the following sections.
	  </para>

      <sect2 id="nse-bitops">
        <title>Bitwise Logical Operations</title>
        <para>
	  Lua does not provide bitwise logical operations. Since they
	  are often useful for low-level network communication, Reuben
	  Thomas' bitwise operation library for Lua has been
	  integrated into NSE. The arguments to the bitwise operation
	  functions should be integers.  The number of bits available
	  for logical operations depends on the data type used to
	  represent Lua numbers&mdash;this is typically 8-byte IEEE
	  floats, which give 53 bits (the size of the mantissa).

	  This implies that the bitwise operations won't work (as expected) 
	  for numbers larger than 10<superscript>14</superscript>. You
	  can use them with 32-bit wide numbers without any problems. Operations
	  involving 64-bit wide numbers, however, may not return the expected
	  result.
	  The logical operations start with <quote>b</quote> (for <literal>bit</literal>) to avoid
	  clashing with reserved words; although <literal>xor</literal> isn't a
	  reserved word, it seemed better to use <literal>bxor</literal> for
	  consistency. In NSE the bitwise functions are in the <literal>bit</literal>
	  namespace.

	  <variablelist>
	    <varlistentry>
	      <term><option>bit.bnot(a)</option>
              <indexterm><primary>bit.bnot(a)</primary></indexterm></term>
	      <listitem>
		<para>
		  Returns the one's complement of a.
		</para>
	    </listitem>
	    </varlistentry>
	    
	    <varlistentry>
	      <term><option>bit.band(w1,...)</option>
		<indexterm><primary>bit.band(w1,...)</primary></indexterm></term>
	      <listitem>
		<para>
		  Returns the bitwise <literal>and</literal> of the
		  w's.
		</para>
	      </listitem>
	    </varlistentry>
	    
	    <varlistentry>
	      <term><option>bit.bor(w1,...)</option>
		<indexterm><primary>bit.bor(w1,...)</primary></indexterm></term>
	      <listitem>
		<para>
		  Returns the bitwise <literal>or</literal> of the w's.
		</para>
	      </listitem>
	    </varlistentry>
	    
	    <varlistentry>
	      <term><option>bit.bxor(w1,...)</option>
		<indexterm><primary>bit.bxor(w1,...)</primary></indexterm></term>
	      <listitem>

		<para>
		  Returns the bitwise <literal>xor</literal> of the
		  w's.
		</para>
	      </listitem>
	    </varlistentry>
	    
	    <varlistentry>
	      <term><option>bit.lshift(a,b)</option>
		<indexterm><primary>bit.lshift(a,b)</primary></indexterm></term>
	      <listitem>
		<para>
		  Returns a shifted left b places&mdash;padded with zeros.
		</para>
	      </listitem>
	    </varlistentry>
	    
	    <varlistentry>
	      <term><option>bit.rshift(a,b)</option>
		<indexterm><primary>bit.rshift(a,b)</primary></indexterm></term>
	      <listitem>
		<para>
		  Returns a shifted logically right b places.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><option>bit.arshift(a,b)</option>
		<indexterm><primary>bit.arshift(a,b)</primary></indexterm></term>
	      <listitem>
		<para>
		  Returns a shifted arithmetically right b places.
		</para>
	      </listitem>
	    </varlistentry>
	    
	    <varlistentry>
	      <term><option>bit.mod(a,b)</option>
		<indexterm><primary>bit.mod(a,b)</primary></indexterm></term>
	      <listitem>
		<para>
		  Returns the integer remainder of a divided by b.
		</para>
	      </listitem>
	    </varlistentry>
	  </variablelist>
	</para>
      </sect2>

      <sect2 id="nse-pcre">
        <title>Perl Compatible Regular Expressions</title>

        <para>
	  One of Lua's quirks is its string patterns. While they have
	  great performance and are tightly integrated into the Lua
	  interpreter, they are very different in syntax and not as
	  powerful as standard regular expressions.  So we have
	  integrated Perl compatible regular expressions into Lua
	  using libPCRE and a modified version of the Lua PCRE library
	  written by Reuben Thomas and Shmuel Zeigerman.  These are
	  the same sort of regular expressions used by Nmap version
	  detection.  The main modification to their library is that
	  the NSE version only supports PCRExpressions instead of both
	  PCRE and POSIX patterns. In order to maintain a high script
	  execution speed, the library interfacing with libPCRE is
	  kept very thin. It is not integrated as seamlessly as the
	  Lua string pattern API. This allows script authors to decide
	  when to use PCRE expressions versus Lua patterns.  PCRE
	  involves a separate pattern compilation step, which saves
	  execution time when patterns are reused.  Compiled patterns
	  can be cached in the NSE registry and reused by other
	  scripts. The PCRE functions reside inside the <literal>pcre</literal> 
	  namespace.
	  </para>

      <warning><para>LibPCRE has a history of security vulnerabilities
      allowing attackers who are able to compile arbitrary regular
      expressions to execute arbitrary code.  More such
      vulnerabilities may be discovered in the future.  These have
      never affected Nmap because it doesn't give attackers any
      control over the regular expressions it uses.  Similarly, NSE
      scripts should never build regular expressions with untrusted
      network input.  Matching hardcoded regular expressions
      <emphasis>against</emphasis> the untrusted input is
      fine.</para></warning>

      <para>The following documentation is derived from that supplied by
      the PCRE Lua lib.</para>

	<variablelist>

	    <varlistentry>
	      <term><option>pcre.new(pattern, flags, locale)</option>
		<indexterm><primary>pcre.new</primary></indexterm></term>
	      <listitem>
		<para>
		  Returns a compiled regular expression. The first
		  argument is a string describing the pattern, such as 
		  <literal>^foo$</literal>.  The second
		  argument is a number describing which compilation
		  flags are set. The compilation flags are set
		  bitwise. If you want to set the 3rd (corresponding to 
		  the number 4) and the 1st (corresponding to 1) bit
		  for example you would pass the number 5 as a second
		  argument. The compilation flags accepted are those 
		  of the PCRE C library. These include flags for case 
		  insensitive matching (1), matching line beginnings (^) 
		  and endings ($) even in multiline strings (i.e. strings 
		  containing <quote>\n</quote>) (2) and a flag for matching across 
		  line boundaries (4). No compilation flags yield a default 
		  value of 0. The third (optional) argument is a string 
		  describing the locale which should be used to compile the 
		  regular expression. The variable is a string which is 
		  passed to the C standard library function
		  <function>setlocale</function>.  For more
		  information on this argument refer to the
		  documentation of <function>setlocale</function>. The
		  resulting compiled regular expression is ready to be
		  matched against strings. Compiled regular
		  expressions are subject to Lua's garbage collection.
		  Generally speaking, <literal>my_regex = pcre.new("<replaceable>pcre-pattern</replaceable>",0,"C")</literal>
		  should do the job most of the time.
		</para>
	      </listitem>
	    </varlistentry>


	    <varlistentry>
	      <term><option>pcre.flags()</option>
		<indexterm><primary>pcre.flags</primary></indexterm></term>
	      <listitem>
		<para>
		  Returns a table of the available PCRE option flags
		  (numbers) keyed by their names (strings). Possible
		  names of the available strings can be retrieved from
		  the documentation of the PCRE library used to link
		  against Nmap. The key is the option name in the
		  manual minus the <literal>PCRE</literal>
		  prefix. <literal>PCRE_CASELESS</literal> becomes
		  <literal>CASELESS</literal> for example.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><option>pcre.version()</option>
		<indexterm><primary>pcre.version</primary></indexterm></term>
	      <listitem>
		<para>
		  Returns the version of the PCRE library in use as a
		  string.  For example <literal>6.4 05-Sep-2005</literal>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><option>pcre_obj:match(string, start, flags)</option>
		<indexterm><primary>pcre.match</primary></indexterm></term>
	      <listitem>
		<para>
		  Returns the start point and the end point point of
		  the first match of the compiled regular expression
		  pcre_obj in the string.  A third
		  returned value is a table which contains
		  <literal>false</literal> in the positions where the
		  pattern did not match. If named sub-patterns were
		  used the table also contains substring matches keyed
		  by their sub-pattern name. Should no match be found the 
		  function returns <literal>nil</literal>.
		  The second and third arguments are optional. The second 
		  argument is a number specifying where the engine should 
		  start trying to apply the pattern. The third argument
		  specifies execution flags for the pattern. 
		  If you want to see if a given string matches a certain expression
		  you could use:</para>

<programlisting>
s = pcre_obj:match("string to be searched", 0,0);
if(s) code_to_be_done_on_match end
</programlisting>

	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><option>pcre_obj:exec(string, start, flags)</option>
		<indexterm><primary>pcre.exec</primary></indexterm></term>
	      <listitem>
		<para>
		  This function is like <literal>match()</literal> except that a table returned as
		  a third result contains offsets of substring matches rather
		  than substring matches themselves. That table will not
		  contain string keys, even if named sub-patterns are used.  For
		  example, if the whole match is at offsets <literal>10, 20</literal> and substring
		  matches are at offsets <literal>12, 14</literal> and <literal>16, 19</literal> then the function
		  returns the following: <literal>10, 20, {12,14,16,19}</literal>
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><option>pcre_obj:gmatch(string, func, n, ef)</option>
		<indexterm><primary>pcre.gmatch</primary></indexterm></term>
	      <listitem>
		<para>
		  Tries to match the regular expression <replaceable>pcre_obj</replaceable> against <replaceable>string</replaceable>
		  up to <replaceable>n</replaceable> times (or as many as possible if <replaceable>n</replaceable> is either
		  not given or is not a positive number), subject to
		  execution flags ef. Each time there is a match, <replaceable>func</replaceable>
		  is called as <replaceable>func(m, t)</replaceable>, where <replaceable>m</replaceable> is the matched
		  string and <replaceable>t</replaceable> is a table of substring matches. This
		  table contains <literal>false</literal> in the
		  positions where the corresponding sub-pattern did
		  not match. If named sub-patterns are used then the
		  table also contains substring matches keyed by their
		  correspondent sub-pattern names (strings).  If <replaceable>func</replaceable>
		  returns a <literal>true</literal> value, then gmatch
		  immediately returns; gmatch returns the number of
		  matches made.
		</para>
	      </listitem>
	    </varlistentry>

	</variablelist>
    </sect2>
	
	<sect2 id="nse-lib-ipOps">
	<title>IP Operations</title>
	<para>
	The <literal>ipOps</literal> module provides some functions for 
	manipulating IPv4 addresses. The functions reside inside the 
	<literal>ipOps</literal> namespace.
	</para>
	<variablelist>
	    <varlistentry>
	      <term><option>bool = ipOps.isPrivate("ip-string")</option>
		  <indexterm><primary>isPrivate</primary></indexterm></term>
	      <listitem>
		  <para>
		  checks whether an IP address, provided as a string in 
		  dotted-quad notation, is part of the non-routed private IP address 
		  space, as described in <ulink role="hidepdf" url="http://www.rfc-editor.org/rfc/rfc1918.txt">RFC 1918</ulink>. These addresses are the well known 
		  <literal>10.0.0.0/8</literal>,<literal>192.168.0.0/16</literal> and
		  <literal>172.16.0.0/12</literal> networks.
		  </para>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><option>DWORD = ipOps.todword("ip-string")</option>
		  <indexterm><primary>todword</primary></indexterm></term>
	      <listitem>
		  <para>
		  returns the IP address as DWORD value (i.e. the IP <replaceable>a.b.c.d</replaceable> becomes
		  <literal>(((a*256+b)*256+c)*256+d)</literal> )
		  </para>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><option>a,b,c,d = ipOps.get_parts_as_number("ip-string")</option>
		  <indexterm><primary>get_parts_as_number</primary></indexterm></term>
	      <listitem>
		  <para>
		  returns 4 numbers corresponding to the fields in dotted-quad notation.
		  For example, <literal>ipOps.get_parts_as_number("192.168.1.1")
		  </literal> returns <literal>192,168,1,1</literal>.
		  </para>
	      </listitem>
	    </varlistentry>
	</variablelist>
	</sect2>
	<sect2 id="nse-lib-shortport">
	<title>Short Portrules</title>
	<para>
	Since portrules are mostly the same for many scripts, the 
        <literal>shortport</literal> module provides functions for the most common tests.
	The arguments in brackets (<literal>[]</literal>) are optional. If no 
        <literal>proto</literal> is provided, <literal>tcp</literal> is used. The default 
	<literal>state</literal> is <literal>open</literal>
	</para>
	<variablelist>
	    <varlistentry>
	      <term><option>shortport.portnumber(port,[proto],[state])</option>
		  <indexterm><primary>portnumber</primary></indexterm></term>
	      <listitem>
		  <para>
		  The port argument is either a number or a table of numbers which are
		  interpreted as port numbers, against which the script should run.
		  </para>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><option>shortport.service(service,[proto],[state])</option>
		  <indexterm><primary>service</primary></indexterm></term>
	      <listitem>
		  <para>
		  The service argument is either a string or a table 
		  of strings which are interpreted as service names
		  (e.g. <literal>"http"</literal>, <literal>"https"</literal>, <literal>"smtp"</literal> or <literal>"ftp"</literal>) against which the
		  script should run. These service names are
		  determined by Nmap's version scan or (if no version
		  scan information is available) the service assigned
		  to the port in <filename>nmap-services</filename>
		  (i.e. "http" for TCP port 80).
		  </para>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><option>shortport.port_or_service(port,service,[proto],[state])</option>
		  <indexterm><primary>port_or_service</primary></indexterm></term>
	      <listitem>
		  <para>
		  This is a combination of the above functions, since many scripts
		  explicitly try to run against the well known ports, but want 
		  also to run against any other port which was discovered to run the 
		  named service. A typical example for this function is: 
		  <literal>portrule = shortport.port_or_service(22,"ssh")</literal>.
		  </para>
	      </listitem>
	    </varlistentry>
	</variablelist>
	</sect2>
	<sect2 id="nse-lib-listop">
	<title>Functional Programming Style List Operations</title>
	<para>
	People used to programming in functional languages, such as Lisp or
	Haskell appreciate their handling of lists very much. The <literal>listop</literal> module tries to bring much of the functionality from
	functional languages to Lua using Lua's central data structure, the table,
	as a base for its list operations. Highlights include a <literal>map</literal> 
	function applying a given function to each element of a list.
	</para>
	<variablelist>
	    <varlistentry>
	      <term><option>bool = listop.is_empty(list)</option>
		  <indexterm><primary>is_empty</primary></indexterm></term>
	      <listitem>
		  <para>
		  Returns <literal>true</literal> if the given list is empty.
		  </para>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><option>bool = listop.is_list(value)</option>
		  <indexterm><primary>is_list</primary></indexterm></term>
	      <listitem>
		  <para>
		  Returns <literal>true</literal> if the given value is a list (or rather a table).
		  </para>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><option>list = listop.map(function, list)</option>
		  <indexterm><primary>map</primary></indexterm></term>
	      <listitem>
		  <para>
		  The provided function is applied to each element of the list 
		  separately. The returned list contains the results of each 
		  function call. For example <literal>listop.map(tostring,{1,2,true})
		  </literal> returns <literal>{"1","2","true"}</literal>.
		  </para>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><option>value = listop.apply(function, list)</option>
		  <indexterm><primary>apply</primary></indexterm></term>
	      <listitem>
		  <para>
		  All of the elements in the list are passed to a call of <literal>
		  function</literal>. The result is then returned. For example
		  <literal>listop.apply(math.max,{1,5,6,7,50000})</literal>
		  yields <literal>50000</literal>.
		  </para>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><option>list = listop.filter(predicate, list)</option>
		  <indexterm><primary>filter</primary></indexterm></term>
	      <listitem>
		  <para>
		  Returns a list containing only those elements for which the predicate
		  returns true. The predicate has to be a function, which takes an 
		  element of the list as argument and the result of which
		  is interpreted as boolean value. If it returns true (or rather 
		  anything besides <literal>false</literal> and <literal>nil</literal>)
		  the argument is appended to the return value of <literal>filter</literal>. 
		  For example: <literal>listop.filter(isnumber,{1,2,3,"foo",4,"bar"})</literal> returns
		  <literal>{1,2,3,4}</literal>.
		  </para>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><option>list = listop.flatten(list)</option>
	      <indexterm><primary>flatten</primary></indexterm></term>
	      <listitem>
		  <para>
		  Since a list can itself contain lists as elements,
		  <literal>flatten</literal> returns a list which
		  only contains values that are not themselves
		  lists. For example:
		  <literal>listop.flatten({1,2,3,"foo",{4,5,{"bar"}}})</literal> returns
		  <literal>{1,2,3,"foo",4,5,"bar"}</literal>.
		  </para>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><option>list = listop.append(list1, list2)</option>
		  <indexterm><primary>append</primary></indexterm></term>
	      <listitem>
		  <para>
		  Returns a list containing all elements of list1 appended by all 
		  elements of <replaceable>list2</replaceable>.
		  </para>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><option>list = listop.cons(value1, value2)</option>
		  <indexterm><primary>cons</primary></indexterm></term>
	      <listitem>
		  <para>
		  Returns a list containing <replaceable>value1</replaceable> appended by <replaceable>value2</replaceable>, which may be
		  of any type.
		  </para>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><option>list = listop.reverse(list)</option>
		  <indexterm><primary>reverse</primary></indexterm></term>
	      <listitem>
		  <para>
		  Returns a list containing all elements of the given list in inverted
		  order.
		  </para>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><option>value = listop.car(list)</option>
		  <indexterm><primary>car</primary></indexterm></term>
	      <listitem>
		  <para>
		  Returns the first element of the given list.
		  </para>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><option>value = listop.ncar(list,n)</option>
		  <indexterm><primary>ncar</primary></indexterm></term>
	      <listitem>
		  <para>
		  Returns the nth (or first if n is omitted) element of the given list.
		  </para>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><option>value = listop.cdr(list)</option>
		  <indexterm><primary>cdr</primary></indexterm></term>
	      <listitem>
		  <para>
		  Returns a list containing all elements but the first of the 
		  given list.
		  </para>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><option>value = listop.ncdr(list, n)</option>
		  <indexterm><primary>ncdr</primary></indexterm></term>
	      <listitem>
		  <para>
		  Returns a list containing all elements but the first n of the 
		  given list, where n is 2 if it is omitted.
		  </para>
	      </listitem>
	    </varlistentry>
	</variablelist>
	</sect2>
	<sect2 id="nse-lib-strbuf">
	<title>String Buffer Operations</title>
	<para>
	Lua's string operations are very flexible and offer an easy-to-use way
	to manipulate strings.  Concatenation using the <literal>..</literal>
	operator is such an operation. The drawback of the built-in API however is the way it handles 
	concatenation of many string values. Since strings in Lua are 
	immutable values, each time you concatenate two strings both get copied
	into the result string. The <literal>strbuf</literal> module offers a
	workaround for this problem, while maintaining the nice syntax. This
	is accomplished by overloading the concatenation operator (<literal>..</literal>) the equality operator (<literal>==</literal>) and the 
	tostring operator.  By overloading
        these operators, we reduce the overhead of using a string buffer instead
        of a plain string to wrap the first literal string assigned to a
        variable inside a <literal>strbuf.new()</literal> call.  Afterwards you can append to the string buffer, or compare
	two string buffers for equality just as you would do with normal strings.
	When looking at the details there are some more restrictions/oddities:
        The concatenation operator requires its left-hand value to be a
        string buffer. Therefore, if you want to prepend a string to a given
        string buffer you have to create a new string buffer out of the string
        you want to prepend.
	The string buffer's <literal>tostring</literal> operator concatenates the 
	strings inside the buffer using newlines by default, since this appears to 
	be the separator used most often.
	</para>
	<variablelist>
	    <varlistentry>
	      <term><option>buffer = strbuf.new("first-string")</option>
		  <indexterm><primary>new</primary></indexterm></term>
	      <listitem>
		  <para>
		  Creates a new string buffer. The argument is optional and is the 
		  first string to be added to the buffer.
		  </para>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><option>buffer = strbuf.concat(strbuf1, value)</option>
		  <indexterm><primary>concat</primary></indexterm></term>
	      <listitem>
		  <para>
		  Concatenates the <literal>value</literal> (which has to be either 
		  a string or a string buffer) to <literal>strbuf1</literal>. This
		  is also the function serving as the string buffer's concatenation operator.
		  The above function call can thus also be expressed as: 
		  <literal>buffer = strbuf1 .. value</literal>
		  </para>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><option>bool = strbuf.eqbuf(strbuf1, strbuf2)</option>
		  <indexterm><primary>eqbuf</primary></indexterm></term>
	      <listitem>
		  <para>
		  Compares <literal>strbuf1</literal> and <literal>strbuf2</literal>
		  for equality. For the function to return <literal>true</literal>, both values must be 
		  string buffers containing exactly the same strings. The <literal>eqbuf</literal> function is called to compare two strings for equality.
		  </para>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><option>strbuf.clear(strbuf)</option>
		  <indexterm><primary>clear</primary></indexterm></term>
	      <listitem>
		  <para>
		  Deletes all strings in <literal>strbuf</literal>.
		  </para>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><option>string = strbuf.dump(strbuf, "delimiter")</option>
		  <indexterm><primary>dump</primary></indexterm></term>
	      <listitem>
		  <para>
		  Dumps <literal>strbuf</literal>'s contents as string. The second 
		  parameter is used as a delimiter between the strings stored inside
		  <literal>strbuf</literal>. <literal>dump(strbuf, "\n")</literal> is 
		  used as the <literal>tostring</literal> function of string buffers.
		  </para>
	      </listitem>
	    </varlistentry>
	</variablelist>
	</sect2>
	<sect2 id="nse-lib-url">
	<title>URL Manipulation Functions</title>

	<para>URL manipulation functions have obvious uses. Fortunately
        there is already an implementation of URL generation functions
        inside the Lua-socket package, which is fairly complete and
        <ulink
        url="http://www.cs.princeton.edu/~diego/professional/luasocket/old/luasocket-2.0-alpha/url.html">well
        documented</ulink>. For NSE, Lua-socket's URL module was
        extended with two functions:</para>

	<variablelist>
	    <varlistentry>
	      <term><option>table = url.parse_query("query-string")</option>
		  <indexterm><primary>parse_query</primary></indexterm></term>
	      <listitem>
		  <para>
		  This function takes a <replaceable>query-string</replaceable> of the form <literal>name1=value1&amp;name2=value2...</literal> and returns a table 
		  containing the name-value pairs, with the <literal>name</literal> 
		  as the key and the <literal>value</literal> as its associated value.
		  The table corresponding to the above <replaceable>query-string</replaceable> would have two 
		  entries: <literal>table["name1"]="value1"</literal> and 
		  <literal>table["name2"]="value2"</literal>.</para>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><option>query_string = url.build_query(table)</option>
		  <indexterm><primary>build_query</primary></indexterm></term>
	      <listitem>
		  <para>
		  This is the inverse function to <literal>parse_query()</literal>.
		  </para>
	      </listitem>
	    </varlistentry>
	</variablelist>
	</sect2>
	<sect2 id="nse-lib-match">
	<title>Buffered Network I/O Helper Functions</title>
	<para>
	The <literal>match</literal> module was written to provide
	functions which can be used for delimiting data received by the
	<literal>receive_buf()</literal> function from the Network I/O API: 
	</para>
	<variablelist>
	    <varlistentry>
	      <term><option>start,end = match.regex("regexpattern")</option>
		  <indexterm><primary>regex</primary></indexterm></term>
	      <listitem>
		  <para>
		  	This is actually a wrapper around NSE' PCRE library <literal>exec</literal> function (see <xref linkend="nse-pcre"/>, thus
			giving script developers the possibility to use regular expressions
			for delimiting instead of Lua's string patterns. If you want to get
			the data in chunks separated by <function>regex</function> (which has to be a valid
			regular expression), you would write <literal>status, val =
			sockobj:receive_buf(match.lua("regex"))</literal>.
		  </para>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><option>start,end = match.numbytes(number)</option>
		  <indexterm><primary>numbytes</primary></indexterm></term>
	      <listitem>
		  <para>
		  	Takes a number as argument and returns that
                        many bytes.  It can be used to get a buffered
                        version of
                        <literal>sockobj:receive_bytes(n)</literal> in
                        case a script requires more than one
                        fixed-size chunk, as the unbuffered version
                        may return more bytes than requested and thus
                        would require you to do the parsing on your
                        own.
		  </para>
	      </listitem>
	    </varlistentry>
	</variablelist>
	</sect2>
	<sect2 id="nse-lib-http">
	<title>HTTP Functions</title>
	<para>
	The <literal>http</literal> module provides functions for dealing with the client side of the http protocol.
	The functions reside inside the <literal>http</literal> namespace.
	The return value of each function in this module is a table with the following keys:
	<literal>status</literal>, <literal>header</literal> and <literal>body</literal>.
	<literal>status</literal> is the status code of the http request
	In case of an error status is <literal>nil</literal>.  <literal>header</literal>
	is a table with the headers received from the server. The header names are
	lower-cased and multiple headers of the same name are concatenated with comma.
	<literal>body</literal> holds a string with the request body.
	</para>
	<variablelist>
	    <varlistentry>
	      <term><option>table = http.get(host,port,path,[options])</option>
		  <indexterm><primary>get</primary></indexterm></term>
	      <listitem>
		  <para>
		  Fetches a resource with a <literal>GET</literal> request.
		  The first argument is either a string with the hostname or a
		  table like the host table passed by nmap. The second argument
		  is either the port number or a table like the port table passed
		  by nmap. The third argument is the path of the resource. The fourth
		  argument is a table for further options. The table may have 2 keys:
		  <literal>timeout</literal> and <literal>header</literal>.
		  <literal>timeout</literal> is the timeout used for the socket
		  operations. <literal>header</literal> is a table with additional
		  headers to be used for the request.
		  The function builds the request and calls <literal>http.request</literal>
		  </para>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><option>table = http.request(host,port,request,[options])</option>
		  <indexterm><primary>request</primary></indexterm></term>
	      <listitem>
		  <para>
		  Sends <literal>request</literal> to <literal>host</literal>:<literal>port</literal>
		  and parses the answer.
		  The first argument is either a string with the hostname or a
		  table like the host table passed by nmap. The second argument
		  is either the port number or a table like the port table passed
		  by nmap. SSL is used for the request if either <literal>port.service</literal>
		  equals <literal>"https"</literal> or <literal>port.version.service_tunnel</literal>
		  equals <literal>"ssl"</literal>.  The third argument is the request. The fourth
		  argument is a table for further options. You can specify a timeout
		  for the socket operations with the timeout key.
		  </para>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><option>table = http.get_url(url,[options])</option>
		  <indexterm><primary>get_url</primary></indexterm></term>
	      <listitem>
		  <para>
		  Parses <literal>url</literal> and calls <literal>http.get</literal>
		  with the result.
		  The second argument is a table for further options. The table may have 2 keys:
		  <literal>timeout</literal> and <literal>header</literal>.
		  <literal>timeout</literal> is the timeout used for the socket
		  operations. <literal>header</literal> is a table with additional
		  headers to be used for the request.
		  </para>
	      </listitem>
	    </varlistentry>
	</variablelist>
	</sect2>
	<sect2 id="nse-lib-datafiles">
	<title>Data File Parsing Functions</title>
	<para>
	The <literal>datafiles</literal> module provides functions for reading and parsing
	Nmap's data files (e.g. <filename>nmap-protocol</filename>, <filename>nmap-rpc</filename>,
	etc.).  These functions' return values are setup for use with exception handling via
	<literal>nmap.new_try()</literal>.
	</para>

	<variablelist>
	    <varlistentry>
	      <term><option>bool, table = datafiles.parse_protocols()</option>
		  <indexterm><primary>parse_protocols</primary></indexterm></term>
	      <listitem>
		  <para>
			This function reads and parses Nmap's <filename>nmap-protocols</filename>
			file.  <literal>bool</literal> is a boolen value indicating success.
			If <literal>bool</literal> is true, then the second returned
			value is a table with protocol numbers indexing the protocol
			names.  If <literal>bool</literal> is false, an error message
			is returned as the second value instead of the table.
		  </para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><option>bool, table = datafiles.parse_rpc()</option>
		  <indexterm><primary>parse_rpc</primary></indexterm></term>
	      <listitem>
		  <para>
			This function reads and parses Nmap's <filename>nmap-rpc</filename>
			file.  <literal>bool</literal> is a boolen value indicating success.
			If <literal>bool</literal> is true, then the second returned
			value is a table with RPC numbers indexing the RPC names.  If
			<literal>bool</literal> is false, an error message is returned
			as the second value instead of the table.
		  </para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><option>bool, table = datafiles.parse_services([protocol])</option>
		  <indexterm><primary>parse_services</primary></indexterm></term>
	      <listitem>
		  <para>
			This function reads and parses Nmap's <filename>nmap-services</filename>
			file.  <literal>bool</literal> is a boolen value indicating success.
			If <literal>bool</literal> is true, then the second returned
			value is a table containing two other tables:
			<literal>tcp{}</literal> and <literal>udp{}</literal>.
			<literal>tcp{}</literal> contains services indexed by TCP port
			numbers.  <literal>udp{}</literal> is the same, but for UDP.
			You can pass "tcp" or "udp" as an argument to
			<literal>parse_services()</literal> to only get the corresponding
			table.  If <literal>bool</literal> is false, an error message is
			returned as the second value instead of the table.
		  </para>
	      </listitem>
	    </varlistentry>
	</variablelist>

	</sect2>
	<sect2 id="nse-lib-stdnse">
	<title>Various Utility Functions</title>
	<para>
	The <literal>stdnse</literal> library contains various handy
	functions which are too small to justify modules of their own:
	</para>
	<variablelist>
	    <varlistentry>
	      <term><option>stdnse.print_debug(...)</option>
		  <indexterm><primary>print_debug</primary></indexterm></term>
	      <listitem>
		  <para>
		  Wrapper function around <literal>print_debug_unformatted()</literal>
		  in the <literal>nmap</literal> namespace. The first argument, if numeric, is 
		  used as the necessary debug level to print the message (it defaults
		  to 1 if omitted). All remaining arguments are processed with
		  Lua's <literal>string.format()</literal> function, which provides a 
		  C-style printf interface.
		  </para>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><option>table = stdnse.strsplit("delimiter","text")</option>
		  <indexterm><primary>strsplit</primary></indexterm></term>
	      <listitem>
		  <para>
		  This function will certainly be appreciated by Perl programmers.
		  It takes two strings as arguments and splits the second one around
		  all occurrences of the first one, returning a table, which contains
		  the substrings without the delimiting string.
		  </para>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term><option>string = stdnse.strjoin("delimiter", table)</option>
		  <indexterm><primary>strjoin</primary></indexterm></term>
	      <listitem>
		  <para>
		  Inverse function to <literal>strsplit()</literal>. Basically this is
		  Lua's <literal>table.concat()</literal> function with the parameters
		  swapped for coherence.
		  </para>
	      </listitem>
	    </varlistentry>
	</variablelist>
	</sect2>
  </sect1>

  <sect1 id="nse-api">
    <title>Nmap API</title>
    <para>
      NSE scripts have access to several Nmap facilities for writing
      flexible and elegant scripts. The API provides target host
      details such as port states and version detection results.  It
      also offers an interface to the Nsock library for efficient
      network I/O.
    </para>

    <sect2 id="nse-api-arguments">
      <title>Information Passed to a Script</title>
      <para>
	An effective Nmap scripting engine requires more than just a
	Lua interpreter. Users need easy access to the information
	Nmap has learned about the target hosts. This data is passed
	as arguments to the NSE <literal>action</literal> method. The
	arguments, <literal>host</literal> and
	<literal>port</literal>, are Lua tables which contain
	information on the target against which the script is
	executed. The following list describes each variable in the
	<literal>host</literal> and <literal>port</literal> tables.
      </para>

      <para>
	<variablelist>
	  <varlistentry>
	    <term><option>host</option>
	      <indexterm><primary>host</primary></indexterm></term>
	    <listitem>
	      <para>
		This table is passed as a parameter to the rule and action
		functions. It contains information on the operating system run by
		the host (if the <option>-O</option> switch was supplied), the
		IP address and the host name of the scanned target.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><option>host.os</option>
	      <indexterm><primary>host.os</primary></indexterm></term>
	    <listitem>
	      <para>
		The <literal>os</literal> entry in the host table is
		an array of strings. The strings (maximally 8) are the
		names of the operating systems the target is possibly
		running. Strings are only entered in this array if the
		target machine is a perfect match for one or more OS
		database entries.  If Nmap was run without the
		<option>-O</option> option, then
		<literal>host.os</literal> is <literal>nil</literal>.
	      </para>
	    </listitem>
	  </varlistentry>
	  
	  <varlistentry>
	    <term><option>host.ip</option>
	      <indexterm><primary>host.ip</primary></indexterm></term>
	    <listitem>
	      <para>Contains a string representation of the IP address of the
		target host. If the scan was run against a host name and the
		reverse DNS query returned more than one IP addresses then the
		same IP address is used as the one chosen for the scan.
	      </para>
	    </listitem>
	  </varlistentry>
	  
	  <varlistentry>
	    <term><option>host.name</option>
	      <indexterm><primary>host.name</primary></indexterm></term>
	    <listitem>
	      <para>Contains the reverse DNS entry of the scanned target host
		represented as a string. If the host has no reverse DNS entry,
		the value of the field is an empty string.
	      </para>
	    </listitem>
	  </varlistentry>
	  <varlistentry>
	    <term><option>host.targetname</option>
	      <indexterm><primary>host.targetname</primary></indexterm></term>
	    <listitem>
	      <para>Contains the name of the host as specified on the commandline.
		If the target given on the commandline contains a netmask or is an IP
		address the value of the field is <literal>nil</literal>.
	      </para>
	    </listitem>
	  </varlistentry>
	  <varlistentry>
	    <term><option>host.directly_connected</option>
	      <indexterm><primary>host.directly_connected</primary></indexterm></term>
	    <listitem>
	      <para> A boolean value indicating whether or not the target host is
		  directly connected (i.e. on the same network segment).
		  </para>
	    </listitem>
	  </varlistentry>
	  <varlistentry>
	    <term><option>host.mac_addr</option>
	      <indexterm><primary>host.mac_addr</primary></indexterm></term>
	    <listitem>
	      <para>MAC address of the destination host (6-byte long binary
		  string) or <literal>nil</literal>, if the host is not directly connected. 
		  </para>
	    </listitem>
	  </varlistentry>
	  <varlistentry>
	    <term><option>host.mac_addr_src</option>
	      <indexterm><primary>host.mac_addr_src</primary></indexterm></term>
	    <listitem>
	      <para>Our own MAC address, which was used to connect to the
		  host (either our network card's, or (with <option>--spoof-mac</option>) the spoofed address).
		  </para>
	    </listitem>
	  </varlistentry>
	  <varlistentry>
	    <term><option>host.interface</option>
	      <indexterm><primary>host.interface</primary></indexterm></term>
	    <listitem>
	      <para>A string containing the interface name (dnet-style) through 
		  which packets to the host are sent.
		  </para>
	    </listitem>
	  </varlistentry>
	  <varlistentry>
	    <term><option>host.bin_ip</option>
	      <indexterm><primary>host.bin_ip</primary></indexterm></term>
	    <listitem>
	      <para>The hosts IP as 4 byte long binary value.
		  </para>
	    </listitem>
	  </varlistentry>
	  <varlistentry>
	    <term><option>host.bin_ip_src</option>
	      <indexterm><primary>host.bin_ip_src</primary></indexterm></term>
	    <listitem>
	      <para>Our hosts IP as 4 byte long binary value.
		  </para>
	    </listitem>
	  </varlistentry>
	  <varlistentry>
	    <term><option>port</option>
	      <indexterm><primary>port</primary></indexterm></term>
	    <listitem>
	      <para>
		The port table is passed to the Lua script in the same
		fashion as the host table. It contains information about the port
		against which the script is running. If the script is run
		according to a host rule, then no port table is passed to the
		script. Port states on the target can still be requested from Nmap
		using the <literal>nmap.get_port_state()</literal> call.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><option>port.number</option>
	      <indexterm><primary>port.number</primary></indexterm></term>
	    <listitem>
	      <para>
		Contains the number of the currently scanned port.
	      </para>
	    </listitem>
	  </varlistentry>

	  
	  <varlistentry>
	    <term><option>port.protocol</option>
	      <indexterm><primary>port.protocol</primary></indexterm></term>
	    <listitem>
	      <para>
		Defines the protocol of the port. Valid values are
		<literal>tcp</literal> and <literal>udp</literal>.
	      </para>
	    </listitem>
	  </varlistentry>

	  
	  <varlistentry>
	    <term><option>port.service</option>
	      <indexterm><primary>port.service</primary></indexterm></term>
	    <listitem>
	      <para>
		Contains a string representation of the service running on
		<literal>port.number</literal> as detected by the Nmap service
		detection. If the <literal>port.version</literal> field is
		<literal>nil</literal> then Nmap has guessed the service based
		only on the port number. Otherwise this field is equal to
		<literal>port.version.name</literal>.
	      </para>
	    </listitem>
	  </varlistentry>
	  
	  <varlistentry>
	    <term><option>port.version</option>
	      <indexterm><primary>port.version</primary></indexterm></term>
	    <listitem>
	      <para>
		This entry is a table which contains information
		retrieved by the Nmap version scanning engine.  Some
		of the values (like service name, service type
		confidence, RPC related values) may be retrieved by
		Nmap even if a version scan was not required.  Values
		which were not retrieved default to
		<literal>nil</literal>.  The meaning of each value is given in the following table:</para>

<table id="scripting-tbl-port-version-values">
 <title><literal>port.version</literal> values</title>
 <tgroup cols="2">
 <colspec colwidth="2*" />
 <colspec colwidth="5*" />
   <thead><row>
    <entry>Name</entry>
    <entry>Description</entry>
   </row></thead>
   <tbody>
   <row>
    <entry><literal>name</literal></entry>
    <entry>Contains the service name Nmap will use for the port.</entry>
   </row>

   <row>
    <entry><literal>name_confidence</literal></entry>
    <entry>Evaluates how confident the version detection is is about the accuracy of <literal>name</literal>, from one (least confident) to 10.</entry>
   </row>

   <row>
    <entry><literal>product</literal>, <literal>version</literal>, <literal>extrainfo</literal>, <literal>hostname</literal>, <literal>ostype</literal>, <literal>devicetype</literal></entry>
    <entry>These five variables are described in
    <bookex><xref linkend="vscan-versioninfo"/>.</bookex>
    <notbook>the <ulink url="http://nmap.org/vscan/vscan-fileformat.html#vscan-versioninfo">versioninfo section</ulink> of our version scanning documentation.</notbook>
   </entry>
   </row>

   <row>
    <entry><literal>service_tunnel</literal></entry>
    <entry>Contains the string <literal>none</literal> or <literal>ssl</literal> based on whether or not Nmap used SSL tunnelling to detect the service.</entry>
   </row>

   <row>
    <entry><literal>service_fp</literal></entry>
    <entry>The service fingerprint, if any, is provided in this value.  This is described in 
<bookex><xref linkend="vscan-community"/>.</bookex>
<notbook>our <ulink url="http://nmap.org/vscan/vscan-community.html">version detection documentation</ulink>.</notbook>
</entry>
   </row>

   <row>
    <entry><literal>rpc_status</literal></entry>
    <entry>Contains a string value of <literal>good_prog</literal> if
           we were able to determine the program number of an RPC
           service listening on the port, <literal>unknown</literal>
           if the port appears to be RPC but we couldn't determine the
           program number, <literal>not_rpc</literal> if the port
           doesn't appear be RPC, or <literal>untested</literal> if we
           haven't checked for RPC status.  The
           <literal>rpc_program</literal>,
           <literal>rpc_lowver</literal>, and
           <literal>rpc_highver</literal> variables are <literal>nil</literal> unless
           <literal>rpc_status</literal> is
           <literal>good_prog</literal>.</entry>
   </row>

   <row>
    <entry><literal>rpc_program</literal>, <literal>rpc_lowver</literal>, <literal>rpc_highver</literal></entry>
    <entry>The detected RPC program number and the range of version
    numbers supported by that program.  These will be
    <literal>nil</literal> if <literal>rpc_status</literal> is
    anything other than <literal>good_prog</literal>.</entry>
   </row>
</tbody></tgroup></table>

	    </listitem>
	  </varlistentry>
	  
	  <varlistentry>
	    <term><option>port.state</option>
	      <indexterm><primary>port.state</primary></indexterm></term>
	    <listitem>
	      <para>
		Contains information on the state of the port.
		Service scripts are only run against ports in the
		<literal>open</literal> or
		<literal>open|filtered</literal> states, so
		<literal>port.state</literal> generally contains one
		of those values. Other values might appear if the port
		table is a result of the
		<literal>get_port_state</literal> function.  You can
		adjust the port state using the
		<literal>nmap.set_port_state()</literal> call.  This is
		normally done when an <literal>open|filtered</literal>
		port is determined to be <literal>open</literal>.
	      </para>
	    </listitem>
	  </varlistentry>


	</variablelist>
      </para>

      <para>
      Scripts also have access to some of Nmap&rsquo;s functions and state
      variables that are exposed through functions in the <literal>nmap</literal>
      table.
      <variablelist>
        <varlistentry>
          <term><option>nmap.debugging()</option>
            <indexterm><primary>debugging</primary><secondary><literal>nmap.debugging</literal></secondary></indexterm></term>
	  <listitem>
	    <para>
            Returns the debugging level as a non-negative integer. The
            debugging level can be set with the <option>-d</option>
            option<bookex> (see <xref linkend="port-scanning-options-output"/>)</bookex>.
            </para>
          </listitem>
        </varlistentry> 
        <varlistentry>
          <term><option>nmap.have_ssl()</option>
            <indexterm><primary>have_ssl</primary></indexterm></term>
	  <listitem>
	    <para>
            Returns true if Nmap was compiled with SSL support, false
            otherwise. This can be used to avoid sending SSL probes
            when SSL is not available.
            </para>
          </listitem>
        </varlistentry> 
        <varlistentry>
          <term><option>nmap.verbosity()</option><indexterm><primary>verbosity</primary><secondary><literal>nmap.verbosity</literal></secondary></indexterm></term>
	  <listitem>
	    <para>
            Returns the verbosity level as a non-negative integer. The
            verbosity level can be set with the <option>-v</option>
            option<bookex> (see <xref linkend="port-scanning-options-output"/>)</bookex>.
            </para>
          </listitem>
        </varlistentry> 
        <varlistentry>
          <term>
            <option>nmap.fetchfile(filename)</option>
            <indexterm><primary>fetchfile</primary></indexterm>
          </term>
	  <listitem>
	    <para>
            Allows access to Nmap's data files.  <literal>fetchfile()</literal>
            searches for the specified file and returns a string containing
            it's path if it is found and readable (to the process).  If the
            file is not found, not readable, or is a directory,
            <literal>nil</literal> is returned.  The call
<programlisting>
nmap.fetchfile("nmap-rpc")
</programlisting>
            will search for the data file <filename>nmap-rpc</filename> and,
            assuming it's found (which it should be), return a location like
            <filename>/usr/local/share/nmap/nmap-rpc</filename>.
            </para>
          </listitem>
        </varlistentry> 
      </variablelist>
      </para>
    </sect2>

    <sect2 id="nse-api-portmethods">
      <title>Target Information Retrieving by a Script</title>
      <para>
	Often the information passed to the script is not enough. Sometimes
	a script might want to correct target information or set it in the
	first place. The following API methods handle this.
      </para>

      <para>
	<variablelist>
	  <varlistentry>
	    <term><option>nmap.get_port_state(host, port, protocol)</option>
	      <indexterm><primary>get_port_state</primary></indexterm></term>
	    <listitem>
	      <para>
		The <literal>get_port_state()</literal> call takes a
		host table, a port table and a protocol
		(<literal>tcp</literal> or <literal>udp</literal>) and
		returns a port table for the queried port. The host
		and port table are similar in structure to the ones
		passed to the rule and action functions. The host
		table should have an IP address field. The port table
		needs a port number and a protocol field. A call could
		look like this:
<programlisting>
nmap.get_port_state({ip="127.0.0.1"}, {number="80", protocol="tcp"})
</programlisting>
		You can of course reuse the host and port tables
		passed to the port rule function. The purpose of this
		call is to be able to match scripts against more than
		one open port. For example if the target host has an
		open port 22 and a running identd server, then you can
		write a script which will only fire if both ports are
		open and there is an identification server on port
		113. While it is possible to specify IP addresses
		different to the currently scanned target, the result
		will only be correct if the target is in the currently
		scanned group of hosts.
		
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><option>nmap.set_port_state(host, port, state)</option>
	      <indexterm><primary>set_port_state</primary></indexterm></term>
	    <listitem>
	      <para>
		The <literal>set_port_state()</literal> call takes a host table,
		a port table, and a port state (<literal>open</literal> or
		<literal>closed</literal>). With this method the final port
		state can be changed. This is useful when Nmap detects a port as
		<literal>open|filtered</literal> but the script successfully connects to it. In this
		case the port state can be set to <literal>open</literal>.  Note 
		that the <literal>port.state</literal> value, which was passed
		to the script's <literal>action</literal> function will not be changed 
		by this call.
	      </para>
	    </listitem>
	  </varlistentry>
	  
	  <varlistentry>
	    <term><option>nmap.set_port_version(host, port, probestate)</option>
	      <indexterm><primary>set_port_version</primary></indexterm></term>
	    <listitem>
	      <para>
		To provide a flexible extension to Nmap's version
		detection NSE scripts can set the version and service
		variables of a port.  
		
		The method takes a host and a port
		table as arguments. The third argument describes the
		state in which the script completed. It is a string
		which is one of: 
		<literal>hardmatched</literal>, 
		<literal>softmatched</literal>, 
		<literal>nomatch</literal>,
		<literal>tcpwrapped</literal>, or 
		<literal>incomplete</literal>. 

		A hard match will almost always be used, as it means
		that the script was able to determine the protocol.
		You can pass in <literal>nomatch</literal> if the
		script fails to match the target port, but it is
		probably already set that way anyway.  One of the
		other states should only be used if you know exactly
		what you are doing.</para>

		<para>The host and port arguments to this function
		should either be the tables passed to the
		<literal>action</literal> method or they should have
		the same structure.  The version detection fields this
		function looks at are <literal>name</literal>,
		<literal>product</literal>,
		<literal>version</literal>,
		<literal>extrainfo</literal>,
		<literal>hostname</literal>,
		<literal>ostype</literal>,
		<literal>devicetype</literal>, and
		<literal>service_tunnel</literal>.  All values in this
		table are optional. It is possible to pass a table in
		which all these values are set to
		<literal>nil</literal> or not to set the values at
		all. 
	      </para>
	    </listitem>
	  </varlistentry>
	</variablelist>
      </para>
    </sect2>
	<sect2 id="nse-aux-raw-packet">
      <title>Various Utility Functions for Raw Packet Support</title>
      <para>
	  NSE has support for sending raw ethernet frames and capturing
	  packets. The following two functions may be handy in this context:
	  </para>
	<variablelist>
	  <varlistentry>
	    <term><option>nmap.clock_ms()</option>
	      <indexterm><primary>nmap.clock_ms()</primary></indexterm></term>
	    <listitem>
	      <para>
	      Returns a number representing the current time as milliseconds 
		  since the start of the epoch (on most systems this is 01/01/1970).
		  </para>
	    </listitem>
	  </varlistentry>
	  <varlistentry>
	    <term><option>nmap.get_interface_link("interface_name")</option>
	      <indexterm><primary>nmap.get_interface_link(interface_name)</primary></indexterm></term>
	    <listitem>
	      <para>
		  For the provided dnet-style
		  <literal>interface_name</literal>,
		  <literal>nmap.get_interface_link()</literal> returns
		  what kind of link level hardware the interface
		  belongs. Return values are:
		  <literal>ethernet</literal>,
		  <literal>loopback</literal> or
		  <literal>p2p</literal>.  If the provided
		  <literal>interface_name</literal> is not one of
		  those types, <literal>nil</literal> is returned.
		  </para>
	    </listitem>
	  </varlistentry>
	</variablelist>
	</sect2>

    <sect2 id="nse-api-networkio">
      <title>Network I/O API</title>
      <para>
	To allow for efficient and parallelizable network I/O, NSE
	provides an interface to Nsock, the Nmap socket library. The
	smart callback mechanism Nsock uses is fully transparent to
	NSE scripts. The main benefit of Nmap-NSE sockets is that they
	never block on I/O operations, allowing many scripts to be run in parallel.
	The I/O parallelism is fully transparent to authors of NSE scripts.  
	In NSE you can either program as if you were using a single non
	blocking socket or you can program as if your connection is
	blocking. Seemingly blocking I/O calls still return once a
	specified timeout has been exceeded. Two flavors of Network I/O are
	supported: 
	</para>
	<sect3 id="nse-api-networkio-connect">
	  <title>Connect-style network I/O</title>
	  <para>This part of the network API should be suitable for most
	  classical network uses: Users create a socket, connect it to a
	  remote address, send and receive data and close the socket again.
	  Everything up to the Transport layer (which is either TCP, UDP or
	  SSL) is handled by the library.  The following socket API methods 
	  are supported:
      </para>

      <para>
	<variablelist>
	  <varlistentry>
	    <term><option>nmap.new_socket()</option>
	      <indexterm><primary>nmap.new_socket()</primary></indexterm></term>
	    <listitem>
	      <para>
		The <literal>new_socket()</literal> Nmap call returns an
		Nmap-NSE socket object which is the recommended method for network
		I/O. It provides facilities to perform communication using the
		UDP, TCP and SSL protocol in a uniform manner. 
	      </para>
	    </listitem>
	  </varlistentry>
	  
	  <varlistentry>
	    <term><option>status, error = socket_object:connect(hostid, port, [protocol])</option>
            <indexterm><primary>connect</primary></indexterm></term>

	    <listitem>
	    
	      <para>
		The connect method of Nmap-NSE socket objects will put
		the socket in a state ready for communication. It
		takes as arguments a host descriptor (either an IP
		address or a host name), a port number and optionally
		a protocol. The protocol must be one of
		<literal>"tcp"</literal>, <literal>"udp"</literal> or
		<literal>"ssl"</literal>. By default the connect call
		will attempt to open a TCP connection. On success the
		returned value of status is
		<literal>true</literal>. If the connection attempt has
		failed, the error value contains a description of the
		error condition stored as a string.
		Those strings are 
		taken from the <function> gai_strerror()</function> 
		C function. They are (with the errorcode in parentheses):</para>
		<itemizedlist>
			<listitem>
			<para><quote>Address family for hostname not supported</quote> (<literal>EAI_ADDRFAMILY</literal>)</para>
			</listitem>
			<listitem>
			<para><quote>Temporary failure in name resolution</quote> (<literal>EAI_AGAIN</literal>)</para>
			</listitem>
			<listitem>
			<para><quote>Bad value for ai_flags</quote> (<literal>EAI_BADFLAGS</literal>)</para>
			</listitem>
			<listitem>
			<para><quote>Non-recoverable failure in name resolution</quote> (<literal>EAI_FAIL</literal>)</para>
			</listitem>
			<listitem>
			<para><quote>ai_family not supported</quote> (<literal>EAI_FAMILY</literal>)</para>
			</listitem>
			<listitem>
			<para><quote>Memory allocation failure</quote> (<literal>EAI_MEMORY</literal>)</para>
			</listitem>
			<listitem>
			<para><quote>No address associated with hostname</quote> (<literal>EAI_NODATA</literal>)</para>
			</listitem>
			<listitem>
			<para><quote>Name or service not known</quote> (<literal>EAI_NONAME</literal>)</para>
			</listitem>
			<listitem>
			<para><quote>Servname not supported for ai_socktype</quote> (<literal>EAI_SERVICE</literal>)</para>
			</listitem>
			<listitem>
			<para><quote>ai_socktype not supported</quote> (<literal>EAI_SOCKTYPE</literal>)</para>
			</listitem>
			<listitem>
			<para><quote>System error</quote> (<literal>EAI_SYSTEM</literal>)</para>
			</listitem>
		</itemizedlist>
<para>In addition to these standard system error based messages are the following two NSE-specific errors:</para>
		<itemizedlist>
			<listitem>
			<para><quote>Sorry, you don't have OpenSSL.</quote> occurs
			if <literal>ssl</literal> is passed as third argument, but Nmap was compiled 
			without OpenSSL support.</para>
			</listitem>
			<listitem>
			<para><quote>invalid connection method</quote> occurs if 
			the second parameter is not one of <literal>tcp</literal>, <literal>udp</literal>, <literal>ssl</literal>.</para>
			</listitem>
		</itemizedlist>
	    </listitem>
	  </varlistentry>
	  
	  <varlistentry>
	    <term><option>status, error = socket_object:send(data)</option>
	      <indexterm><primary>send</primary></indexterm></term>
	    <listitem>
	      <para>
		The send method sends the data contained in the
		<literal>data</literal> string through an open
		connection. On success the returned value of status is
		<literal>true</literal>.  If the send operation
		has failed, the error value contains a description of
		the error condition stored as a string. The error strings are:
		<itemizedlist>
		<listitem>
			<para><quote>Trying to send through a closed socket</quote>&mdash;if there was no 
			call to socket_object:connect before the send operation.</para>
		</listitem>
		<listitem>
			<para><quote>TIMEOUT</quote>&mdash;if the operation took longer than the 
			specified timeout for the socket.</para>
		</listitem>
		<listitem>
			<para><quote>ERROR</quote>&mdash;if an error occurred inside the underlying 
			Nsock library.</para>
		</listitem>
		<listitem>
			<para><quote>CANCELLED</quote>&mdash;if the operation was cancelled.</para>
		</listitem>
		<listitem>
			<para><quote>KILL</quote>&mdash;if for example the script scan is aborted due
			to a faulty script.</para>
		</listitem>
		<listitem>
			<para><quote>EOF</quote>&mdash;if an EOF was read&mdash;will probably not occur 
			for a send operation.</para>
		</listitem>

		</itemizedlist>
	      </para>
	    </listitem>
	  </varlistentry>
	  
	  <varlistentry>
	    <term><option>status, value = socket_object:receive()</option>
	      <indexterm><primary>receive</primary></indexterm></term>
	    <listitem>
	      <para>
		The receive method does a non-blocking receive operation on
		an open socket. On success the returned value of
		<literal>status</literal> is
		<literal>true</literal> and the received data is stored in
		<literal>value</literal>. If receiving data has failed,
		<literal>value</literal> contains a description of the error
		condition stored as a string. A failure occurs for example
		if receive is called on a closed socket. The receive call
		returns to the NSE script all the data currently stored
		in the receive buffer of the socket. Error conditions
		are the same as for the send operation.
	      </para>
	    </listitem>
	  </varlistentry>
	  
	  <varlistentry>
	    <term><option>status, value = socket_object:receive_lines(n)</option>
	      <indexterm><primary>receive_lines</primary></indexterm></term>
	    <listitem>
	      <para>
		Tries to receive at least <replaceable>n</replaceable>
		lines from an open connection. A line is a string
		delimited with <literal><quote>\n</quote></literal> characters.  If
		it was not possible to receive at least
		<replaceable>n</replaceable> lines before the operation times
		out a TIMEOUT error occurs. On the other hand, if more
		than <replaceable>n</replaceable> lines were received, all are
		returned, not just <replaceable>n</replaceable>. On success
		the returned value of <replaceable>status</replaceable> is
		<literal>true</literal> and the received data is
		stored in <replaceable>value</replaceable>. If the connection
		attempt has failed, <replaceable>value</replaceable> contains
		a description of the error condition stored as string.
		Error conditions are the same as for the send operation.

	      </para>
	    </listitem>
	  </varlistentry>
	  
	  <varlistentry>
	    <term><option>status, value = socket_object:receive_bytes(n)</option>
	      <indexterm><primary>receive_bytes</primary></indexterm></term>
	    <listitem>
	      <para>
		Tries to receive at least <replaceable>n</replaceable>
		bytes from an open connection. On success the returned
		value of <replaceable>status</replaceable> is <literal>true</literal> and the
		received data is stored in
		<replaceable>value</replaceable>. If operation fails,
		<replaceable>value</replaceable> contains a description of the
		error condition stored as a string. Similarly to
		<literal>receive_lines()</literal>
		<replaceable>n</replaceable> is the minimum amount of
		characters we would like to receive. If more arrive,
		we get all of them. If less than <replaceable>n</replaceable> characters arrive
		before the operation times out, a TIMEOUT error occurs.
		Other error conditions are the same as for the send operation. 

	      </para>
	    </listitem>
	  </varlistentry>
	  
	  <varlistentry>
	    <term><option>status, value = socket_object:receive_buf(func/"string", keeppattern)</option>
	      <indexterm><primary>receive_buf</primary></indexterm></term>
	    <listitem>
	      <para>
	      <literal>receive_buf</literal> tries to circumvent several 
		  limitations in the other <literal>receive*</literal> functions.
		  <literal>receive_line(n)</literal>, for example, tries to ensure that 
		  there are at least <replaceable>n</replaceable> lines received and returns everything it has 
		  already read from the connection (even though there may be much more
		  data than requested). It also leaves line-parsing to the user.</para>

 
               <para><literal>receive_buf</literal> on the other hand returns only the
		  part of the received data until the first match of a delimiter,
		  with the rest being saved inside a buffer for later calls to
		  <literal>receive_buf</literal>. This buffer gets cleared on calls to
		  other functions inside the Network I/O API.  Should the data not 
		  contain the delimiter another read request is sent and the buffer is 
		  checked again when more data is present.</para>

                <para><literal>receive_buf</literal> takes two arguments. 
                  The first one is either a string or a function. If it is 
		  a string it gets passed to Lua's <literal><ulink url="http://www.lua.org/manual/5.1/manual.html#5.4">string.find</ulink></literal> function as the (second) pattern
		  parameter, with the buffer data being searched. If it is a function
		  it is expected to take exactly one parameter (the buffer) and its
		  return values have to be like those of <literal>string.find</literal>
		  (i.e. offsets of the start and the end of the delimiter inside the
		  buffer, or <literal>nil</literal>, if the delimiter is not found).</para>

		  <para>The second argument is a boolean value which indicates whether the 
		  delimiting pattern should be returned along with the received data or 
		  discarded.</para>

                  <para>A module inside the
		  nselib <literal>match.lua</literal> (<xref linkend="nse-lib-match"/>) provides
		  functions for matching received data against regular expressions or
		  for receiving a defined number of bytes. <literal>receive_buf</literal>'s return values behave exactly as the return values of
the other <literal>receive*</literal> functions. Two values are returned (status,val)&mdash;
the first indicating whether the request was successful, the other
containing the returned data (or the case of a failure, an error message).</para>

                  <para>Possible error messages are those of the other
		  <literal>receive*</literal> functions and, in addition, the following:
		<itemizedlist>
		<listitem>
			<para><quote>Error inside splitting-function</quote>&mdash;if the first argument was
			a function which caused an error while being called.
			</para>
		</listitem>
		<listitem>
			<para><quote>Error in <literal>string.find</literal> (<literal>nsockobj:receive_buf</literal>)!</quote>&mdash;if a string
			was provided as the first argument, and string.find() yielded an
			error while being called.</para>
		</listitem>
		<listitem>
			<para><quote>Expected either a function or a string!</quote>&mdash;if the 
			first argument was neither a function nor a string.</para>
		</listitem>
		<listitem>
			<para><quote>Delimiter has negative size!</quote>&mdash;if the returned start offset
			is greater than the end offset.</para>
		</listitem>
		</itemizedlist>
		  </para>

		</listitem>
	  </varlistentry>
	  
	  <varlistentry>
	    <term><option>status, err = socket_object:close()</option>
	      <indexterm><primary>close</primary></indexterm></term>
	    <listitem>
	      <para>
		Closes an open connection. On success the returned value of
		<literal>status</literal> is <literal>true</literal>. If the connection 
		attempt has failed, <literal>value</literal> contains a description 
		of the error condition stored as a string. Currently the only error 
		message is: <quote>Trying to close a closed socket</quote>, which is issued if the socket
		has already been closed. Sockets are subject to garbage collection. 
		Should you forget to close a socket, it will get closed before it gets
		deleted (on the next occasion Lua's garbage collector is run).
		However since garbage collection cycles are difficult to predict, it 
		is considered good practice to close opened sockets.		
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><option>status,localip,localport,remoteip,remoteport=socket_object:get_info()</option>
	      <indexterm><primary>get_info</primary></indexterm></term>
	    <listitem>
	      <para>
		This function returns information about the socket
		object. It returns 5 values. If an error occurred, the
		first value is <literal>nil</literal> and the second
		value describes the error condition. Otherwise the
		first value describes the success of the operation and
		the remaining 4 values describe both endpoints of the
		TCP connection. If you put the call in a <literal>try()</literal> statement
		the status value is consumed. The call can be used for example if
		you want to query an authentication server.
	      </para>
	    </listitem>
	  </varlistentry>

	  
	  <varlistentry>
	    <term><option>socket_object:set_timeout(t)</option>
	      <indexterm><primary>set_timeout</primary></indexterm></term>
	    <listitem>
	      <para>
		Sets the time, in milliseconds, after which input and
		output operations on a socket should time out and
		return. The default value is 30,000 (30 seconds). The lowest
		allowed value is 10ms, since this is 
		the granularity of NSE network I/O.
	      </para>
	    </listitem>
	  </varlistentry>

	</variablelist>
      </para>
    </sect3>
	<sect3 id="nse-api-networkio-raw">
	  <title>Raw packet network I/O</title>
	  <para>For those cases where the connection oriented approach is too inflexible,
	  NSE provides script developers with a more powerful option:
	  raw packet network I/O. The greater flexibility comes, however, at
	  the cost of a slightly more complex API. Receiving raw packets is
	  accomplished via a wrapper around Libpcap inside
	  the Nsock library. In order to keep the
	  capturing efficient it works in a three tiered approach: Opening a
	  device for capturing, registering listeners to it and receiving
	  packets. With each call to <literal>pcap_open()</literal> you have
	  to provide a callback function, which receives the packet (along with
	  it's layer 2 and 3 headers) and is used to compute a so-called
	  packet hash. Each call to <literal>pcap_register()</literal> takes a
	  binary string as argument. For every packet captured the computed
	  hash is matched against all registered strings. 
	  Those scripts for which the compare yields true are then provided
	  with the packet as a return value to <literal>pcap_receive()</literal>. 
	  The more general the packet hash computing function is kept, 
	  the more scripts may receive the packet and proceed with their
	  execution.  To use the packet capturing inside your script you have to 
	  create (and afterwards close) a socket with
	  <literal>nmap.newsocket()</literal> 
	  (or <literal>socket_object:close()</literal> respectively)&mdash;just
	  like with the connection-based network I/O. A more detailed description 
	  of the functions for packet capturing follows:
      </para>

      <para>
	<variablelist>
	  <varlistentry>
	    <term><option>socket_object:pcap_open(device, snaplen, promisc,
		test_function, bpf)</option>
	      <indexterm><primary>pcap_open</primary></indexterm></term>
	    <listitem>
	      <para>
		The <literal>pcap_open()</literal> call opens the socket for
		packet capturing. The parameters are:</para>
<itemizedlist>
<listitem><para><literal>device</literal>&mdash;the dnet-style interface name of the device you want to capture from.</para></listitem>
<listitem><para><literal>snaplen</literal>&mdash;defines the length of each packet you want to capture (similar to the <option>-s</option> option to <command>tcpdump</command>)</para></listitem>
<listitem><para><literal>promisc</literal>&mdash;should be set to <literal>1</literal> if the interface should activate promiscuous mode, and zero otherwise.</para></listitem>
<listitem><para><literal>test_function</literal>&mdash;callback function used to compute the <literal>packet-hash</literal></para></listitem>
<listitem><para><literal>bpf</literal>&mdash;a string describing a Berkeley packet filter expression (like those provided to <command>tcpdump</command>)</para></listitem>
</itemizedlist>
	    </listitem>
	  </varlistentry>
	  <varlistentry>
	    <term><option>socket_object:pcap_register(packet-hash)</option>
	      <indexterm><primary>pcap_register</primary></indexterm></term>
	    <listitem>
	      <para>
		  Starts the listening for incoming packages. The provided
		  <literal>packet-hash</literal> is a binary string which has to
		  match the hash returned by the
		  <literal>test_function</literal> parameter provided to
		  <literal>pcap_open()</literal>. If you want to receive all
		  packets, just provide the empty string (<literal>""</literal>).
		  There has to be a call to <literal>pcap_register()</literal>
		  before a call to <literal>pcap_receive()</literal>.
	      </para>
	    </listitem>
	  </varlistentry>
	  <varlistentry>
	    <term><option>status, packet_len, l2_data, l3_data = socket_object:pcap_receive()</option>
	      <indexterm><primary>pcap_receive</primary></indexterm></term>
	    <listitem>
	      <para>
		  Receives a captured packet. If successful, the return values are:</para>
<itemizedlist>
<listitem><para><literal>status</literal>&mdash;a boolean with the value <literal>true</literal>.</para></listitem>
<listitem><para><literal>packet_len</literal>&mdash;the length of the captured packet (note, that you could have received less data if the snaplen parameter was smaller than the packet length)</para></listitem>
<listitem><para><literal>l2_data</literal>&mdash;data from the second OSI layer (e.g. ethernet headers)</para></listitem>
<listitem><para><literal>l3_data</literal>&mdash;data from the third OSI layer (e.g. IPv4 headers).</para></listitem>
</itemizedlist>

<para>Should an error or timeout occur, while waiting for a packet the
return values are: <literal>nil,error_message,nil,nil</literal>, where
error_message describes the occurred error.</para>

	    </listitem>
	  </varlistentry>
	  <varlistentry>
	    <term><option>socket_object:pcap_close()</option>
	      <indexterm><primary>pcap_close()</primary></indexterm></term>
	    <listitem>
	      <para>Closes the pcap device.
	      </para>
	    </listitem>
	  </varlistentry>
	</variablelist>  
	</para>
	<para>
	Receiving raw packets is a great feature, but it is also only the
	half job. Now for sending raw packets: To accomplish this NSE has
	access to a wrapper around the <literal>dnet</literal> library.
	Currently NSE has the ability to send raw ethernet frames via the
	following API:
	</para>
	<para>
	<variablelist>
	  <varlistentry>
	    <term><option>dnet_object=nmap.new_dnet()</option>
	      <indexterm><primary>new_dnet()</primary></indexterm></term>
	    <listitem>
	      <para>
	      Creates and returns a new dnet_object, which can be used to
		  send raw packets.
		  </para>
	    </listitem>
	  </varlistentry>
	  <varlistentry>
	    <term><option>dnet_object:ethernet_open(interface_name)</option>
	      <indexterm><primary>ethernet_open</primary></indexterm></term>
	    <listitem>
	      <para>Opens the interface defined by the provided 
		  <replaceable>interface_name</replaceable> for sending ethernet frames
		  through it. An error (<quote>device is not valid ethernet
		  interface</quote>) is thrown in case the provided argument
		  is not valid.
		  </para>
	    </listitem>
	  </varlistentry>
	  <varlistentry>
	    <term><option>dnet_object:ethernet_send(packet)</option>
	      <indexterm><primary>ethernet_send</primary></indexterm></term>
	    <listitem>
	      <para>
		  Sends the provided data as ethernet frame across the previously
		  opened interface. Note that you have to provide the packet
		  including IP header and ethernet header. If there was no
		  previous valid call to <literal>ethernet_open()</literal> an
		  error is thrown (<quote>dnet is not valid opened ethernet
		  interface</quote>).
		  </para>
	    </listitem>
	  </varlistentry>
	  <varlistentry>
	    <term><option>dnet_object:ethernet_close()</option>
	      <indexterm><primary>ethernet_close</primary></indexterm></term>
	    <listitem>
	      <para>Closes the interface. The only error which may be thrown
		  is the same as for the <literal>ethernet_send()</literal>
		  operation.
		  </para>
	    </listitem>
	  </varlistentry>
	</variablelist>
	</para>
	</sect3>
	</sect2>
    <sect2 id="nse-exceptions">
      <title>Exception Handling</title>
      <para>
	  NSE provides an exception handling mechanism not present in
	  the plain Lua language. The exception handling is tailored
	  specifically for network I/O operations. The mechanism
	  follows a functional programming paradigm rather than an
	  object oriented programming paradigm. To create an exception
	  handler the <literal>nmap.new_try()</literal> API method is
	  used. This method returns a function, which takes a function
	  as an argument. If the function passed as an argument raises
	  an exception, then the script execution is aborted and no
	  output is produced. Optionally you can pass a function to
	  the <literal>new_try()</literal> method which will be called
	  if an exception is caught. In this function you can perform
	  required clean up operations.</para>

      <para>
	  <xref linkend="nse-exception-handling"/> shows cleanup
	  exception handling at work.  A new function named
	  <literal>catch</literal> is defined to simply close the
	  newly created socket in case of an error.  It is then used
	  to protect connection and communication attempts on that
	  socket. If no catch function is specified, execution of the
	  script aborts without further ado&mdash;open sockets
	  will remain open. If the verbosity level is at least one
	  or if the scan is performed in debugging mode a description
	  of the uncaught error condition is printed on standard output.
	  Note that it is currently not easily possible to group several
	  statements in one try block. It is also important to remember
	  that if the socket is not closed it will occupy memory
	  until the next run of Lua's garbage collector.

	</para>

        <example id="nse-exception-handling">
          <title>Exception handling example</title>
<programlisting>
local result, socket, try, catch

result = ""
socket = nmap.new_socket()
catch = function() 
socket:close() 
end
try = nmap.newtry(catch)

try(socket:connect(host.ip, port.number))
result = try(socket:receive_lines(1));
try(socket:send(result))
</programlisting>
       </example>
	
	  <para>
	  Writing a function which is treated properly by the
	  try/catch mechanism is straightforward. The function should
	  return multiple values.  The first value should be a boolean
	  which is <literal>true</literal> upon successful completion of the function and
	  <literal>false</literal> otherwise. If the function completed successfully the try
	  construct consumes the indicator value and returns the
	  remaining values.  If the function failed then the second
	  returned value must be a string describing the error
	  condition. Note that that if the value is not <literal>nil</literal> it is
	  treated as <literal>true</literal> so you can return your
	  value in the normal case and return <literal>nil, <replaceable>error description</replaceable></literal>
	  if an error occurs.
	</para>

    </sect2>

    <sect2 id="nse-api-registry">
      <title>The Registry<indexterm><primary>registry</primary></indexterm></title>
      <para>
	The registry is a normal Lua table. What is special about it
	is that it is visible by all scripts and it retains its state
	between script executions. Nmap does not scan every host
	specified on the command line at the same time, it puts them
	in smaller groups and these groups are scanned in parallel.  The
	registry is rebuilt for every group, so information stored
	there is only deleted after NSE finishes processing the
	current target group. This implies of course that the registry
	is transient&mdash;it is not stored between Nmap executions. Every
	script can read the registry and write to it. If a script is
	running after another script, it can read some information in
	the registry which was left by the first script. This feature
	is particularly powerful in combination with the run level
	concept. A script with a higher run level can rely on entries
	left behind for it by scripts with lower run levels.  Remember
	however that the registry can be written by all scripts
	equally, so choose the keys for your entries wisely. The
	registry is stored in <literal>nmap.registry</literal>. The
	behavior of the registry allows caching of already calculated
	data. The cache can be seen by all scripts until the registry
	is rebuilt with the next target group. <!-- If for example you have
	compiled a regular expression, you can store the compiled
	expression in the registry so that scripts which need the same
	pattern do not have to recompile it. -->

      </para>
    </sect2>
  </sect1>

  <sect1 id="nse-tutorial">
    <title>Script Writing Tutorial</title>

    <para>
      Suppose that you are convinced of the power of NSE. How do you
      go about writing your own script?  Let's say
      that you want to extract information from an identification
      server.  Nmap used to have this functionality but it was removed
      because of inconsistencies in the code base. Fortunately, the
      protocol identd uses is pretty simple. Unfortunately, it is too
      complicated to be expressible in Nmap's version detection
      language. Let's look at how the identification protocol
      works. First you connect to the identification server. Next you
      send a query of the form <literal><replaceable>port-on-server</replaceable>,
      <replaceable>port-on-client</replaceable></literal> terminated with a new line
      character. The server should then respond with a string of the
      form <literal><replaceable>port-on-server</replaceable>, <replaceable>port-on-client</replaceable>:<replaceable>response-type</replaceable>:<replaceable>address-information</replaceable></literal>.  In case of an error the address
      information is omitted. This description is sufficient for our
      purposes, for more details refer to <ulink role="hidepdf" url="http://www.rfc-editor.org/rfc/rfc1413.txt">RFC 1413</ulink>.  The protocol cannot be modeled in Nmap's version
      detection language for two reasons. The first is that you need
      to know both the local and the remote port of a
      connection. Version detection does not provide this data.  The
      second, more severe obstacle, is that you need two open
      connections to the target&mdash;one to the identification server and
      one to the port you want to query. Both obstacles are easily
      overcome with NSE.  </para>

    <para>
      The anatomy of a script is described in <xref linkend="nse-scripts"/>.
      In this section we will show how the described structure is utilized.
    </para>
    
    <sect2 id="nse-tutorial-head">
      <title>The Head</title>
      <para>
	The head of the script is essentially its meta
	information. This includes the fields
	<literal>id</literal>, <literal>description</literal>,
	<literal>author</literal>, <literal>license</literal> and
	<literal>categories</literal>. We are not going to change the
	run level for now. The <literal>id</literal> of a script
	should uniquely identify it. If it is absent, the path to the
	script will be used as an id. We recommend to choose an id
	which concisely identifies the purpose of the script, since
	the ID is printed before the script's results in Nmap output.
      </para>
      <para>
<programlisting>
id = "Service Owner"
</programlisting>
      </para>
      <para>
	The description field should contain a sentence or two describing what the script does.  If anything about the script results might confuse or mislead users, and you can't eliminate the issue by improving the script or results text, it should be documented in the <literal>description</literal> string.
      </para>
      <para>
<programlisting>
description = "Opens a connection to the scanned port, opens a connection to \
port 113, queries the owner of the service on the scanned port and prints it."
</programlisting>
      </para>
      <para>

 	Users must tell the Lua interpreter that the string
	continues on the following line by ending the line with a
	backslash (&lsquo;<literal>\</literal>&rsquo;). They must also decide what
	categories the script belongs to. This script is a good
	example of a script which cannot be categorized clearly. It is
	<literal>safe</literal> because we are not using the service
	for anything it was not intended for.  On the other hand, it
	is <literal>intrusive</literal> because we connect to a
	service on the target and therefore potentially give out
	information about us.  To solve this dilemma we will place our
	script in two categories:

      </para>
<programlisting>
categories = {"safe", "intrusive"}
</programlisting>
    </sect2>

    <sect2 id="nse-tutorial-rule">
      <title>The Rule</title>
      <para>
	The rule section is a Lua method which decides when the
	script's action should be performed and when it should be
	skipped. Usually this decision is based on the host and port
	information passed to the rule function. In the case of the
	identification script it is slightly more complicated than
	that. To decide whether to run the identification script on a
	given port we need to know if there is an identification
	server running on the target machine. Or more formally: the
	script should be run if (and only if) the currently scanned TCP port is open and
	TCP port 113 is also open. For now we will rely on the fact that
	identification servers listen on TCP port 113. Unfortunately NSE
	only gives us information about the currently scanned port.

	To find out if port 113 is open we are going to use the
	<literal>nmap.get_port_state()</literal> method. If the identd
	port was not scanned, the <literal>get_port_state</literal>
	function returns <literal>nil</literal>. So we need to make
	sure that the table is not <literal>nil</literal>. We also
	check if both ports are in the <literal>open</literal> state.
	If this is the case, the action is executed, otherwise we skip
	the action.
      </para>
      <para>
<programlisting>
portrule = function(host, port)
local identd, decision

local ident_port = { number=113, protocol="tcp" }
identd = nmap.get_port_state(host, ident_port)

if
 identd ~= nil and identd.state == "open" and port.state == "open"
then
 decision = true
else
 decision = false
end

return decision
end
</programlisting>
      </para>

      <para>
	This rule is <emphasis>almost</emphasis> correct, but still
	slightly buggy. Can you find the bug?  It is a pretty subtle
	one. The problem is that this script fires on any kind of open
	port, TCP or UDP. The <literal>connect()</literal> method on
	the other hand assumes a TCP protocol unless it is explicitly
	told to use another protocol. Since the identification service
	is only defined for TCP connections, we need to narrow down
	the range of ports which fire our script. Our new rule only
	runs the script if the port is open, we are looking at a TCP
	port, and TCP port 113 is open. Writing the new and
	improved port rule is left as an exercise to the reader (or
	peek at the script in the latest Nmap distribution).
      </para>


    </sect2>

    <sect2 id="nse-tutorial-action">
      <title>The Mechanism</title>
      <para>
	At last we implement the actual functionality. The script will
	first connect to the port on which we expect to find the
	identification server, then it will connect to the port we
	want information about. Afterward we construct a query string
	and parse the response. If we received a satisfactory
	response, we return the retrieved information.
      </para>
      <para>
	First we need to create two socket objects. These objects
	represent the sockets we are going to use. By using object methods
	like 
	<literal>open()</literal>, 
	<literal>close()</literal>, 
	<literal>send()</literal> or
	<literal>receive()</literal> we can operate on the network
	socket. To avoid excessive error checking code we use NSE's
	exception handling mechanism. We create a function which will
	be executed if an error occurs and call this function
	<literal>catch</literal>. Using this function we generate
	a <literal>try</literal> function. The <literal>try</literal>
	function will call the <literal>catch</literal> function
	whenever there is an error condition in the tried block. Note
	that we could have ignored the last two return values
	of <literal>client_service:get_info()</literal> like this: 

<programlisting>
local localip, localport  = client_service:get_info()
</programlisting>
	This would have sufficed because we know that the remote port is
	stored in <literal>port.number</literal>.</para>

        <para>In this example we
	prefer not to tell the user if the query resulted in an
	error. To inform users of failed
	identification queries, simply uncomment the corresponding
	line. It is necessary that we assign the variable <literal>owner</literal>
	a <literal>nil</literal> value because returning <literal>nil</literal>
	is the only way to tell the script engine to suppress script output.
      </para>
      
      <para>
	<programlisting>
action = function(host, port)
local owner = ""

local client_ident = nmap.new_socket()
local client_service = nmap.new_socket()

local catch = function()
  client_ident:close()
  client_service:close()
end

local try = nmap.newtry(catch)

try(client_ident:connect(host.ip, 113))
try(client_service:connect(host.ip, port.number))

local localip, localport, remoteip, 
remoteport = client_service:get_info()

local request = port.number .. ", " .. localport .. "\n"

try(client_ident:send(request))

owner = try(client_ident:receive_lines(1))

if string.match(owner, "ERROR") then
  owner = nil
  --  owner = "Service owner could not be determined: " .. owner
else
 owner = string.match(owner, "USERID : .+ : (.+)\n", 1)
end

try(client_ident:close())
try(client_service:close())

return owner
end
</programlisting>
      </para>
    </sect2>
  </sect1>

  <sect1 id="nse-vscan">
    <title>Version Detection using NSE</title>
    <para>

      The version detection system built into Nmap was designed to
      efficiently recognize the vast majority of protocols with a
      simple pattern matching syntax.  Some protocols require a more
      complex approach, and a generalized scripting language is
      perfect for this.  Skype2 is one such protocol.  It pretends to
      be an http server, requiring multiple queries to determine its
      true nature.  NSE has been integrated into Nmap's version
      detection framework to handle these cases. The scripts which
      extend the version scanner belong to the reserved category
      <literal>version</literal>.  This category cannot be run from
      the command line.  It is only executed if the user has required a
      version scan. The following listing shows a simple script which
      demonstrates the use of the NSE version detection API. If either
      the TCP port 80 is open or the service has been determined to be
      http, the script is triggered. Although it could be extended to
      recognize different http servers, its only purpose is to show off
      the version detection API. It is not advisable to use NSE for
      version detection in the simple case of http servers. The
      version detection variables have been filled with dummy entries
      to illustrate their effect on the Nmap output.</para> 


      <para>
<programlisting> 
description = "Demonstration of a version detection NSE script. It checks \
and reports the version of a remote web server. For real life purposes it is \
better to use Nmap version detection (-sV)."
author = "Diman Todorov &lt;diman.todorov@gmail.at&gt;
license = "See Nmap's COPYING for license"

id = "HTTP version"

categories = {"version"}

runlevel = 1.0

portrule = function(host, port)
  if (port.number == 80
      or port.service == "http" )
      and port.protocol == "tcp" 
  then
    return true
  else
    return false
  end
end

action = function(host, port)
  local query = "GET / HTTP/2.1\r\n"
  query = query .. "Accept: */*\r\n"
  query = query .. "Accept-Language: en\r\n"
  query = query .. "User-Agent: Nmap NSE\r\n"
  query = query .. "Host: " .. host.ip .. ":" .. port.number .. "\r\n\r\n"

  local socket = nmap.new_socket()
  local catch = function()
    socket:close()
  end

  local try = nmap.new_try(catch)

  try(socket:connect(host.ip, port.number))
  try(socket:send(query))

  local response = ""
  local lines
  local status
  local value

  while true do
    status, lines = socket:receive_lines(1)

    if not status or value then
      break
    end

    response = response .. lines
    value = string.match(response, "Server: (.-)\n")
  end

  try(socket:close())

  if value then
    port.version.name = "[Name]"
    port.version.name_confidence = 10
    port.version.product = "[Product]"
    port.version.version = "[Version]"
    port.version.extrainfo = "[ExtraInfo]"
    port.version.hostname = "[HostName]"
    port.version.ostype = "[OSType]"
    port.version.devicetype = "[DeviceType]"

    port.version.service_tunnel = "none"
    port.version.fingerprint = nil
    nmap.setPortVersion(host, port, "hardmatched")
  end
end
      </programlisting>
    </para>
    <para>
	This is what the output of this script looks like:
      <screen>
$ ./nmap -sV localhost -p 80

Starting Nmap ( http://insecure.org )
Interesting ports on localhost (127.0.0.1):
PORT   STATE SERVICE VERSION
80/tcp open  [Name]  [Product] [Version] ([ExtraInfo])
Service Info: Host: [HostName]; OS: [OSType]; Device: [DeviceType]

Nmap finished: 1 IP address (1 host up) scanned in 9.317 seconds
</screen>
    </para>
    <para>
      The name variable denotes the detected protocol name.
      The product, version and extrainfo variables are used
      to produce a human readable description of the server
      version. The remaining variables provide information deduced
      from the output of the server concerning the target host.
    </para>
  </sect1>

  <sect1 id="nse-example-scripts">
    <title>Example Scripts</title>
    <para>
      <remark>
	This section should probably provide 2&ndash;3 scripts
	which show a diverse and interesting set of NSE features.  Each
	script should probably have its own sect2 containing a brief
	description of the script and anything noteworthy about it,
	followed by the script itself with annotations (lineannotation
	tag) as you can see, for example, at 
	<ulink url="http://nmap.org/vscan/vscan-technique-demo.html"/>.
      </remark>
    </para>

    <para>

    <remark>
    DT: perhaps include an optional version field
    </remark>

    </para>
    <sect2 id="nse-example-script-finger">
      <title>Finger-Test Script</title>
	  <para>The finger script (<filename>finger.nse</filename>) is a perfect
      example of how short typical NSE scripts are.
	  </para>

 <para>first the information fields are filled out, note that the 
<literal>id</literal> field is kept short, this is important since it is 
printed in Nmap's output. A detailed description of what the script
actually does should go in the <literal>description</literal> field.</para>
<programlisting>
id="Finger Results"

description="attempts to get a list of usernames via the finger service"

author = "Eddie Bell &lt;ejlbell@gmail.com&gt;"

license = "See nmaps COPYING for licence"
</programlisting>

<para>The <literal>categories</literal> field is a table
containing all the categories the script belongs to&mdash;These are used for
script selection through the <option>--script</option> option.</para>

<programlisting>
categories = {"discovery"}
</programlisting>

<para>You can use the facilities provided by the nselib (<xref
linkend="nse-library"/>) by <literal>requiring</literal> them.  Here
we want to use shorter port rules.</para>

<programlisting>
require "shortport"
</programlisting>

<para>We want to check whether the service behind the port is finger,
or whether it runs on finger's well known port 79. Through this we can
use the information gathered during the version scan (if finger runs
on a non-standard port) or still run against at least the port we
expect it, should the version detection information not be available.</para>

<programlisting>
portrule = shortport.port_or_service(79, "finger")

action = function(host, port)
  local socket = nmap.new_socket()
  local results = ""
  local status = true
</programlisting>

<para>The function <literal>err_catch()</literal> will be called for
clean up, through NSE's exception handling mechanism. Here it only
closes the previously opened socket (which should be enough in most
cases).</para>

<programlisting>
local err_catch = function()
  socket:close()
end
</programlisting>

<para>The clean up function gets registered for exception handling via
a call to <literal>nmap.new_try()</literal></para>

<programlisting>
  local try = nmap.new_try(err_catch())
</programlisting>

<para>The script sets a timeout of 5000, which is equivalent to 50
seconds. Should any operation require more time we'll receive a
<literal>TIMEOUT</literal> error message.</para>

<programlisting>
  socket:set_timeout(5000)
</programlisting>

<para>For actually using exception handling we need to wrap calls to
functions, which may return an error inside
<literal>try()</literal></para>

<programlisting>
  try(socket:connect(host.ip, port.number, port.protocol))
  try(socket:send("\n\r"))
</programlisting>

<para>The call to <literal>receive_lines()</literal> is not wrapped in
<literal>try()</literal>, because we don't want to abort the script
just because we didn't receive the data we expected. Note that there
is less data than requested (100 lines), we still receive it and the
status is <literal>true</literal> &mdash;consequent calls would yield
a <literal>false</literal> status.</para>

<programlisting>
  status, results = socket:receive_lines(100)
  socket:close()
</programlisting>

<para>The script returns a string only if we got the data we
wanted, otherwise <literal>nil</literal> is returned (automatically, since
scripts return one result).</para>

<programlisting>
  if not(status) then
    return results
  end
end
</programlisting>
</sect2>

	<sect2 id="nse-example-script-owner">
      <title>Service Owner Lookup via Identd</title>
	  <para><filename>showOwner.nse</filename> demonstrates the flexibility
	  of the NSE, which is unmatched by other parts of Nmap. If the target
	  is running an <literal>identd</literal> daemon it connects to it for
	  each running service and tries to identify its owner.
	  </para>
<programlisting>
id = "Service owner"

description = "Opens a connection to the scanned port, opens a connection to \
port 113, queries the owner of the service on the scanned port and prints it."

author = "Diman Todorov &lt;diman.todorov@gmail.com&gt;"

license = "See nmaps COPYING for licence"

categories = {"safe"}

</programlisting>

<para>Portrules are not restricted to those provided by the 
short-port module (<xref linkend="nse-lib-shortport"/>).
They can be any function taking a host- and a porttable as argument and 
returning a boolean.
</para>

<programlisting>
portrule = function(host, port) 
  local identd, decision
</programlisting>

<para>In order to determine the state of a port, which is not provided
as argument we just have to construct a table describing the port
(i.e. its number and the protocol it's using) and pass it to
<literal>nmap.get_port_state()</literal> which returns a table filled
with the information Nmap has about the port.</para>

<programlisting>
  local auth_port = { number=113, protocol="tcp" }
  identd = nmap.get_port_state(host, auth_port)

  if 
    identd ~= nil
    and identd.state == "open" 
  then
    decision = true
  else
    decision = false
  end

  return decision
end

action = function(host, port)
  local owner = ""
</programlisting>

<para>Scripts can open any number of connection they want.</para>

<programlisting>
  local client_ident = nmap.new_socket()
  local client_service = nmap.new_socket()

  local catch = function()
    client_ident:close()
    client_service:close()
  end

  local try = nmap.new_try(catch)

  try(client_ident:connect(host.ip, 113))
  try(client_service:connect(host.ip, port.number))

  local localip,localport,remoteip,remoteport = try(client_service:get_info())

  local request = port.number .. ", " .. localport .. "\n"

  try(client_ident:send(request))

  owner = try(client_ident:receive_lines(1))

  if string.match(owner, "ERROR") then 
    owner = nil
  else
    owner = string.match(owner, "USERID : .+ : (.+)\n", 1)
  end

  try(client_ident:close())
  try(client_service:close())

  return owner
end
</programlisting>
	</sect2>
  </sect1>
  <sect1 id="nse-implementation">
    <title>Implementation</title>
    <para>
      <remark>
	We don't need a dozen pages of low-level trivial
	details, but it would be nice to have a few sections
	describing notable aspects of the NSE implementation (maybe
	things like how the parallelization algorithms work, how Lua
	is embedded, performance related notes.  Information which
	might help script writers is particularly desirable.  I tend
	to think reasons for choosing Lua may be better suited to
	<xref linkend="nse-lua"/>, but it could be placed here
	instead.
      </remark>
    </para>
	<para>
	Now how does all this work? The following section describes
	some interesting aspects of the NSE. While the focus primarily lies on 
	giving script writers a better feeling of what happens with scripts, it 
	should also provide a starting point for understanding (and extending) the 
	NSE sources.
	</para>
    <sect2 id="nse-implementation-init">
      <title>Initialization Phase</title>
      <para>
      During its initialization stage, Nmap loads the Lua interpreter and its provided 
	  libraries get loaded. These libraries are:</para>
		<itemizedlist>
		<listitem>
			<para>The <emphasis>package</emphasis> library (namespace: 
			<literal>package</literal>)&mdash;Lua's 
			<ulink url="http://www.lua.org/manual/5.1/manual.html#5.3">package-lib</ulink> provides (among others) the <literal>require</literal> function, used to load modules from the
			nselib.
			</para>
		</listitem>
		<listitem>
			<para>The <emphasis>table</emphasis> library (namespace: 
			<literal>table</literal>)&mdash;The 
			<ulink url="http://www.lua.org/manual/5.1/manual.html#5.5">table manipulation library</ulink> contains many functions used
			to operate on <literal>tables</literal>&mdash;Lua's central data 
			structure.
			</para>
		</listitem>
		<listitem>
			<para>The <emphasis>I/O</emphasis> library (namespace: 
			<literal>io</literal>)&mdash;The 
			<ulink url="http://www.lua.org/manual/5.1/manual.html#5.7">Input/Output library</ulink> offers functions such as reading files and reading the output from programs you execute.
			</para>
		</listitem>
		<listitem>
			<para>The <emphasis>OS</emphasis> library (namespace: 
			<literal>os</literal>)&mdash;The 
			<ulink url="http://www.lua.org/manual/5.1/manual.html#5.8">Operating System lib</ulink> provides facilities of the operating 
			system, including filesystem operations (renaming/removing files,
			creating of temporary filenames) and access to the environment.
			</para>
		</listitem>
		<listitem>
			<para>The <emphasis>string</emphasis> library (namespace: 
			<literal>string</literal>)&mdash;The 
			<ulink url="http://www.lua.org/manual/5.1/manual.html#5.4">
			string library </ulink> helps you with functions used to manipulate
			strings inside Lua. Functions include: printf-style 
			string formating, pattern matching using Lua-style patterns, 
			substring extraction, etc.
			</para>
		</listitem>
		<listitem>
			<para>The <emphasis>math</emphasis> library (namespace: 
			<literal>math</literal>)&mdash;Since usually numbers in Lua correspond
			to the <literal>double</literal> C-type, the 
			<ulink url="http://www.lua.org/manual/5.1/manual.html#5.6">math library</ulink> gives you access to rounding functions, 
			trigonometric functions, random number generation, and many more.
			</para>
		</listitem>
		<listitem>
			<para>The <emphasis>debug</emphasis> library (namespace: 
			<literal>debug</literal>)&mdash;The 
			<ulink url="http://www.lua.org/manual/5.1/manual.html#5.9">debug library</ulink> provides you with a somewhat lower level API
			to the Lua-interpreter. Through it you can access functions along 
			the execution stack, get function closures and object metatables,
			etc. 
			</para>
		</listitem>
	    </itemizedlist>

<para>In addition to loading the libraries provided with Lua, the functions
in the <literal>nmap</literal> namespace also get loaded. and search
path for modules is set to the default one prepended by the nselib
directory (which is searched in the locations Nmap searches for its
data files and scripts).  In this step the provided script arguments
also get stored inside the <literal>registry</literal>.</para>

		<para>
		The next phase of NSE initialization is loading the chosen
		scripts, which are the arguments provided to the 
		<option>--script</option> option or <literal>safe,intrusive</literal>, in 
		case of a default script scan.  The string <literal>version</literal> 
		is appended, if version detection was enabled.
		The arguments afterwards are tried to be 
		interpreted as script categories. This is done via a short Lua function
		hard-coded into <filename>nse_init.cc</filename> called <literal>Entry</literal>. If you take a look into the <filename>script.db</filename> you'll see that the <literal>Entry</literal> lines inside
		it are Lua function calls with a table as argument. 
The arguments that didn't produce any filenames are then interpreted
as file or directory names themselves.  If this also fails, the script scan is aborted.</para>

		<para>
		In the next stage the found files are loaded as chunks, each with
		its own environment, having read but not write access to the global
		name space and saved inside two globally accessible Lua tables: 
		<literal>hosttests</literal> and <literal>porttests</literal> 
		depending on the type of script. Because scripts only get loaded once, values stored inside variables during a script's execution against one host or port can be accessed when the same script runs against another target.   This can be used to save computation time when a script is run
against multiple targets. See <xref linkend="nse-example-persistent-locals"/>.

 
During this stage scripts are
also are also provided with a default <literal>runlevel</literal> (1.0), if they
don't specify one themselves and a check is performed whether they
contain an <literal>action</literal> and a <literal>description</literal> field.
</para>

<example id="nse-example-persistent-locals">
<title>Using local variables to save data.</title>
<programlisting>
id="persistent locals example"
description="This sample script shows how data can be stored across \
several invocations of a script against multiple targets"
author="Stoiko Ivanov"
categories = {"safe"}

require "shortport"
portrule = shortport.portnumber(80)
-- we have to declare the variable in the script's global scope
-- because if we declare it inside the action it would get redefined
-- with each call to the action 
local filecontent = nil
require "strbuf"
action= function(host, port)
  if(filecontent == nil) then
    filecontent = strbuf.new()
    for line in io.lines("a_filename_we_want_to_read_from")
      filecontent = filecontent .. line
    end
  end
  --rest of the script doing something with the filecontent, we just
  --read
end
</programlisting>
</example>
    </sect2>
    
	<sect2 id="nse-implementation-match">
      <title>Matching of Scripts to Targets</title>
      <para>
	  After the initialization is finished the <literal>hostrules</literal> and
	  <literal>portrules</literal> are evaluated for each host in the current
	  target group. At this check a list is built which contains the combinations of scripts and the hosts they will run against.

It should be noted that the rules of all chosen scripts are
checked against all hosts and their <literal>open</literal> and <literal>open|filtered</literal> ports.
Therefore it is advisable to leave the rules as simple as possible and
to do all the computation inside the <literal>action</literal>, as a script will only be
executed if it is run against a specific target. After the check those script-target combinations  get their own <ulink url="http://www.lua.org/manual/5.1/manual.html#2.11">Lua-thread</ulink> which is anchored in Lua's C-API <ulink url="http://www.lua.org/manual/5.1/manual.html#3.5">registry</ulink> to prevent their garbage collection. These <literal>thread_records</literal> are afterwards sorted by run level and all script-target combinations of one run level are stored in a list, in order to ensure that scripts with a higher run level are run after those with a lower one.</para>

    </sect2>

	<sect2 id="nse-implementation-run">
      <title>Running Scripts</title>
      <para>
      Now to the actual script scanning, and the way NSE accomplishes 
	  parallelization. Lua, through its concept of 
	  <ulink url="http://www.lua.org/manual/5.1/manual.html#2.11">coroutines
	  </ulink> offers collaborative multi-threading, which means that scripts
	  can suspend themselves, at defined points, and let other coroutines 
	  execute. Since network I/O, especially waiting for responses from
	  remote host, is the part of scripts which would consume most time with
	  waiting, this is the point where scripts suspend themselves and let
	  others execute. Each call to some of the functions of the Nsock wrapper 
	   causes the calling script to yield (pause). Once the request is processed by the Nsock library, the 
	  callback causes the script to be pushed from the waiting queue to the
	  running queue, which will eventually let it resume its operation.
	  </para>
    </sect2>
	<sect2 id="nse-implementation-c-modules">
      <title>Adding C Modules to Nselib</title>
      <para>
	  This section tries to give a short walk-through to adding
	  nselib modules written in C (or C++) to Nmap's build system, since
	  this has shown to be sometimes tedious. Writing C modules is
	  described at length in <ulink
	  url="http://www.amazon.com/exec/obidos/ASIN/8590379825/secbks-20">Programming
	  in Lua, Second Edition</ulink>.  Basically C modules consist of the
	  functions they provide to Lua, which have to be of type <ulink url="http://www.lua.org/manual/5.1/manual.html#lua_CFunction">lua_CFunction</ulink>. Additionally they have to contain a function
	  which is used to actually open the module. By convention these function names are <literal>luaopen_<replaceable>modulename</replaceable></literal>.
	  A good starting point for writing such modules is provided with
	  <filename>bit.c</filename> and <filename>pcre.c</filename> inside
	  the <filename>nselib/</filename> subdirectory of Nmap's source tree, 
	  which are two C modules already provided by the nselib. C modules
	  basically are shared libraries which get loaded at runtime by Lua. 
	  </para>
	  <para>
	  The Unix build system uses <literal>libtool</literal> for
	  compilation in a platform independent way.

 As long as the new module
	  does not depend on foreign libraries, you should only need to add
	  <literal><replaceable>modulename</replaceable>.so</literal> to the
	  <literal>all</literal> and <literal>clean</literal> targets in 
	  <filename>Makefile.in</filename>
	  and copy and adapt the lines from <filename>bit.so</filename>.
          If your module does have dependencies you will most probably have to
	  add checks for those libraries to <filename>configure.ac</filename>
	  and put the dependencies inside the <literal>libtool</literal>
	  commands in <filename>Makefile.in</filename>&mdash;here you should
	  take a look at how <literal>pcre.so</literal> handles this. 
	  So much for the way it should work. Now for some pitfalls we've
	  come across so far: These are results from building shared libraries in 
	  general and not really specific to nselib. Linking with
	  static libraries (e.g. <literal>libnbase</literal>) sometimes leads
	  to problems with exporting symbols on some platforms (in our case
	  this was a x86_64-linux platform). To our knowledge no such
	  problems occur when linking against already existing shared
	  libraries. 
	  </para>
	  <para>
	  The Windows build system requires C module developers to create a
	  MS Visual Studio Project file for their module
	  (<filename>&lt;modulename&gt;.vcproj</filename>) inside the
	  <filename>nselib</filename> subdirectory. On Windows you have to
	  include the <filename>liblua/</filename> subdirectory as
	  an additional include path as well as a library search path. In addition
	  you have to tell the project to link against the
	  <filename>liblua.lib</filename> static library provided with Nmap.
	  Other properties of the project should be the same as for other
	  nselib C modules (e.g. see <filename>nse_bitlib.vcproj</filename>).
	  Afterwards you have to include the newly created project file in
	  Nmap's Visual Studio solution file
	  (<filename>mswin32\nmap.sln</filename>) and make sure that
	  <filename>nse_bitlib.vcproj</filename> depends on your project,
          because it is there nselib-modules get copied to their final destinations and are included in Nmap.
	  </para>
	</sect2>
  </sect1>
  <sect1 id="nse-license">
    <title>NSE Script License and Community Contributions</title>
    <para>

      <remark>Fyodor is working on this.  The general idea is for scripts to be contributed
	and distributed under the same license as Nmap, as described
	in <ulink url="http://seclists.org/nmap-dev/2006/q3/0156.html">this
	nmap-dev post</ulink>.  We certainly welcome script contributions!</remark>

    </para>
  </sect1>