Handle https://example.com:80 and http://example.com:443 cases

The shortport.ssl check can be expensive (6-second timeout on HTTP
services if you don't use -sV), so we want to avoid it if possible. As
discussed at
b2deb019ed (commitcomment-30289632)
this commit restores the SSL check in cases where it might matter (http
and https default ports) and adds a bypass when the URI scheme is
explicitly requested, as in http.get_url and when following redirects.

nselib/http.lua

@@ -170,15 +170,31 @@ local get_default_port = url.get_default_port
 
 --- Get a value suitable for the Host header field.
 -- See RFC 2616 sections 14.23 and 5.2.
-local function get_host_field(host, port)
+local function get_host_field(host, port, scheme)
+  -- If the global header is set by script-arg, use that.
   if host_header then return host_header end
+  -- If there's no host, we can't invent a name.
   if not host then return nil end
   local number = (type(port) == "number") and port or port.number
-  if number == 443 or number == 80 then
-    return stdnse.get_hostname(host)
+  if scheme then
+    -- Caller provided scheme. If it's default, return just the hostname.
+    if number == get_default_port(scheme) then
+      return stdnse.get_hostname(host)
+    end
   else
-    return stdnse.get_hostname(host) .. ":" .. number
+    scheme = url.get_default_scheme(port)
+    if scheme then
+      -- Caller did not provide scheme, and this port has a default scheme.
+      local ssl_port = shortport.ssl(host, port)
+      if (ssl_port and scheme == 'https') or
+        (not ssl_port and scheme == 'http') then
+        -- If it's SSL and https, or if it's plaintext and http, return just the hostname.
+        return stdnse.get_hostname(host)
+      end
+    end
   end
+  -- No special cases matched, so include the port number in the host header
+  return stdnse.get_hostname(host) .. ":" .. number
 end
 
 -- Skip *( SP | HT ) starting at offset. See RFC 2616, section 2.2.
@@ -366,6 +382,11 @@ local function validate_options(options)
         stdnse.debug1("http: options.redirect_ok must be a function or boolean or number")
         bad = true
       end
+    elseif(key == 'scheme') then
+      if type(value) ~= 'string' then
+        stdnse.debug1("http: options.scheme must be a string")
+        bad = true
+      end
     else
       stdnse.debug1("http: Unknown key in the options table: %s", key)
     end
@@ -1086,7 +1107,7 @@ local function build_request(host, port, method, path, options)
   local mod_options = {
     header = {
       Connection = "close",
-      Host = get_host_field(host, port),
+      Host = get_host_field(host, port, options.scheme),
       ["User-Agent"]  = USER_AGENT
     }
   }
@@ -1604,6 +1625,7 @@ function get(host, port, path, options)
   if(not(validate_options(options))) then
     return http_error("Options failed to validate.")
   end
+  options = options or {}
   local redir_check = get_redirect_ok(host, port, options)
   local response, state, location
   local u = { host = host, port = port, path = path }
@@ -1617,6 +1639,8 @@ function get(host, port, path, options)
     if ( not(u) ) then
       break
     end
+    -- Allow redirect to change scheme (e.g. redirect to https)
+    options.scheme = u.scheme or options.scheme
     location = location or {}
     table.insert(location, response.header.location)
   until( not(redir_check(u)) )
@@ -1640,6 +1664,7 @@ function get_url( u, options )
 
   port.service = parsed.scheme
   port.number = parsed.port or get_default_port(parsed.scheme) or 80
+  options.scheme = options.scheme or parsed.scheme
 
   local path = parsed.path or "/"
   if parsed.query then
@@ -1678,6 +1703,7 @@ function head(host, port, path, options)
   if(not(validate_options(options))) then
     return http_error("Options failed to validate.")
   end
+  options = options or {}
   local redir_check = get_redirect_ok(host, port, options)
   local response, state, location
   local u = { host = host, port = port, path = path }
@@ -1691,6 +1717,8 @@ function head(host, port, path, options)
     if ( not(u) ) then
       break
     end
+    -- Allow redirect to change scheme (e.g. redirect to https)
+    options.scheme = u.scheme or options.scheme
     location = location or {}
     table.insert(location, response.header.location)
   until( not(redir_check(u)) )

nselib/url.lua

@@ -415,11 +415,31 @@ local get_default_port_ports = {http=80, https=443}
 -- @param scheme for determining the port, such as "http" or "https".
 -- @return A port number as an integer, such as 443 for scheme "https",
 --         or nil in case of an undefined scheme
------------------------------------------------------------------------------
 function get_default_port (scheme)
   return get_default_port_ports[(scheme or ""):lower()]
 end
 
+local function invert(t)
+  local out = {}
+  for k, v in pairs(t) do
+    out[v] = k
+  end
+  return out
+end
+
+get_default_scheme_schemes = invert(get_default_port_ports)
+
+---
+-- Provides the default URI scheme for a given port.
+--
+-- @param port A port number as a number or port table
+-- @return scheme for addressing the port, such as "http" or "https".
+-----------------------------------------------------------------------------
+function get_default_scheme (port)
+  local number = (type(port) == "number") and port or port.number
+  return get_default_scheme_schemes[port]
+end
+
 if not unittest.testing() then
   return _ENV
 end