Some comm.lua internal changes

1. export the comm.opencon function. Does all the connect/request
timeout, recv_before, and first data payload stuff that tryssl does, but
without trying SSL. Ought to save some boilerplate in some scripts

2. Make opencon use setup_connect instead of duplicating code.

3. Move a debug message about tryssl to tryssl from opencon

4. Transparently handle UDP in tryssl, in case someone does that. Debug
message about DTLS not being supported is printed, but otherwise just
connects with opencon. Previously, doing this would result in a
connection to the TCP version of the port, even if you passed in a port
table with port.protocol=="udp".

nselib/comm.lua

@@ -182,6 +182,10 @@ end
 -- @return Worst option ("tcp" or "ssl")
 local function bestoption(port)
     if type(port) == 'table' then
+      if port.protocol == "udp" then
+        stdnse.debug2("DTLS (SSL over UDP) is not supported")
+        return "udp", "udp"
+      end
         if port.version and port.version.service_tunnel and port.version.service_tunnel == "ssl" then return "ssl","tcp" end
         if port.version and port.version.name_confidence and port.version.name_confidence > 6 then return "tcp","ssl" end
         if is_ssl(port) then return "ssl","tcp" end
@@ -198,40 +202,29 @@ end
 -- Possible options:
 -- timeout, connect_timeout, request_timeout: See module documentation
 -- recv_before: receive data before sending first payload
+-- proto: the protocol to use ("tcp", "udp", or "ssl")
 --
 -- @param host The destination host IP
 -- @param port The destination host port
--- @param protocol The protocol for the connection
 -- @param data The first data payload of the connection
+-- @param opts An options table
 -- @return sd The socket descriptor, nil if no connection is established
 -- @return response The response received for the payload
 -- @return early_resp If opt recv_before is true, returns the value
 -- of the first receive (before sending data)
-local function opencon(host, port, protocol, data, opts)
-    local sd = nmap.new_socket()
-
-    local connect_timeout, request_timeout = get_timeouts(host, opts)
-
-    sd:set_timeout(connect_timeout)
-
-    local status = sd:connect(host, port, protocol)
+function opencon(host, port, data, opts)
+  local status, sd = setup_connect(host, port, opts)
     if not status then
           sd:close()
           return nil, nil, nil
         end
 
-    sd:set_timeout(request_timeout)
-
     local response, early_resp;
     if opts and opts.recv_before then status, early_resp = read(sd, opts) end
     if data and #data > 0 then
         sd:send(data)
         status, response = sd:receive()
     else
-        if not (opts and opts.recv_before) then
-            stdnse.debug1("Using comm.tryssl without either first data payload or opts.recv_before." ..
-                         "\nImpossible to test the connection for the correct protocol!")
-        end
         response = early_resp
     end
     if not status then
@@ -260,11 +253,24 @@ end
 -- @return earlyResp If opt recv_before is true, returns the value
 -- of the first receive (before sending data)
 function tryssl(host, port, data, opts)
+  opts = opts or {}
+  if not data or opts.recv_before then
+    stdnse.debug1(
+      "Using comm.tryssl without either first data payload or opts.recv_before.\n\z
+      Impossible to test the connection for the correct protocol!"
+      )
+  end
     local opt1, opt2 = bestoption(port)
     local best = opt1
-    local sd, response, early_resp = opencon(host, port, opt1, data, opts)
-    if not sd then
-        sd, response, early_resp = opencon(host, port, opt2, data, opts)
+    if opts.proto=="udp" then
+      stdnse.debug2("DTLS (SSL over UDP) is not supported")
+    end
+    opts.proto = opt1
+    local sd, response, early_resp = opencon(host, port, data, opts)
+    -- Try the second option (If udp, then both options are the same; skip it)
+    if not sd and opt1 ~= "udp" then
+        opts.proto = opt2
+        sd, response, early_resp = opencon(host, port, data, opts)
         best = opt2
     end
     if not sd then best = "none" end