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Enable multiple UDP connections in listen mode. Fixes #1223

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dmiller
2022-10-10 20:48:14 +00:00
parent 1641a291e9
commit 4e6c8feb15
8 changed files with 104 additions and 402 deletions
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4
ncat/docs/ncat.xml
View File

@@ -327,8 +327,8 @@
particularly handy for talking to SSL enabled HTTP servers, etc.</para>
<para>In server mode, this option listens for incoming SSL connections,
rather than plain untunneled traffic.</para>
<para>In UDP connect mode, this option enables Datagram TLS (DTLS).
This is not supported in server mode.</para>
<para>In UDP mode, this option enables Datagram TLS (DTLS).
</para>
</listitem>
</varlistentry>

30
ncat/docs/ncatguide.xml
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@@ -131,9 +131,7 @@ the tool? Many of these examples suppose a Unix environment. -->
to the connection limit. With <option>--keep-open</option> (or
<option>-k</option> for short), the server receives everything sent by
any of its clients, and anything the server sends is sent to all of
them. A UDP server will communicate with only one client (the first
one to send it data), because in UDP there is no list of
<quote>connected</quote> clients.
them.
</para>
<para>
@@ -304,12 +302,9 @@ Content-Type: text/html; charset=UTF-8
the User Datagram Protocol, is an unreliable protocol often used by
applications that can't afford the overhead of TCP. Use the
<option>--udp</option><indexterm><primary><option>--udp</option> (Ncat option)</primary></indexterm>
option to make Ncat use UDP. In listen mode, Ncat will communicate
with only one client, and the
<option>--keep-open</option><indexterm><primary><option>--keep-open</option> (Ncat option)</primary><secondary>not supported with UDP</secondary></indexterm>
option doesn't work, the reason for this being that UDP has no notion
of a connection. UDP may be secured by a form of SSL called Datagram TLS (DTLS)<indexterm><primary>DTLS</primary><secondary>Datagram TLS</secondary></indexterm>.
This is currently only supported in connect (client) mode.<indexterm><primary>SSL</primary><secondary>not supported with UDP in server mode</secondary></indexterm>
option to make Ncat use UDP.
UDP may be secured using the <option>--ssl</option> option, which enables
Datagram TLS (DTLS)<indexterm><primary>DTLS</primary><secondary>Datagram TLS</secondary></indexterm>.
</para>
<para>
@@ -646,8 +641,8 @@ print("Hello, world!")
combined with
<option>--keep-open</option>,<indexterm><primary><option>--keep-open (Ncat option)</option></primary><secondary>with <option>--exec</option></secondary></indexterm>
Ncat will accept multiple connections, forking off a new handler for
each. This works even in UDP mode; the usual limit of only one client
doesn't apply. The server will keep running until you press
each.
The server will keep running until you press
<keycombo><keycap>ctrl</keycap><keycap>C</keycap></keycombo> or
otherwise terminate it externally. In this way Ncat can work much like
inetd.<indexterm><primary>inetd</primary></indexterm>
@@ -1779,20 +1774,17 @@ host1$ <userinput>ncat --send-only host2 &lt; log.txt</userinput>
<term>UDP discard server</term>
<listitem>
<literallayout>
<command>ncat -l 9 --keep-open --udp --sh-exec "cat > /dev/null"</command>
<command>ncat --udp -l --keep-open 9 --recv-only > /dev/null</command>
</literallayout>
</listitem>
</varlistentry>
</variablelist>
<para>
With the TCP server we used <option>--keep-open</option> so the server
could handle multiple simultaneous connections, not just one. For the
UDP server we had to use <option>--sh-exec</option> to allow multiple
concurrent connections. Recall from <xref linkend="ncat-usage"/> that
a UDP server can handle only one client but with
<option>--exec</option> and <option>--sh-exec</option> this limitation
does not apply.
Ncat in UDP mode uses all the same options as TCP. The caveat here is that
connections can't be closed, only timed out, so you will eventually run out
of sockets if you do not use a timeout. Currently, none of the timeout
options do the appropriate thing in this instance. </para>
</para>
<para>