When nmap.connect gets a port table, let port.protocol be the default

protocol (instead of always "tcp"). You can still override it by
providing an explicit protocol after the table.

nse_nsock.cc

@@ -652,6 +652,7 @@ static int l_nsock_connect(lua_State * L)
 {
   enum type {TCP, UDP, SSL};
   static const char * const op[] = {"tcp", "udp", "ssl", NULL};
+  const char *default_proto = "tcp";
 
   l_nsock_udata *udata = (l_nsock_udata *) luaL_checkudata(L, 1, "nsock");
   const char *addr, *targetname;
@@ -696,12 +697,18 @@ static int l_nsock_connect(lua_State * L)
       luaL_error(L, "port.number is not numeric");
     port = lua_tointeger(L, -1);
     lua_pop(L, 1);
+
+    lua_getfield(L, 3, "protocol");
+    /* Make this the default if the "proto" argument isn't given. */
+    if (lua_isstring(L, -1))
+      default_proto = lua_tostring(L, -1);
+    lua_pop(L, 1);
   } else {
     port = (unsigned short) luaL_checkint(L, 3);
   }
 
   /* proto argument. */
-  what = luaL_checkoption(L, 4, "tcp", op);
+  what = luaL_checkoption(L, 4, default_proto, op);
 
   const char *error;
   struct addrinfo *dest;

nselib/nmap.luadoc

@@ -281,7 +281,7 @@ function condvar(object)
 --   socket:close()
 -- end
 -- try = nmap.new_try(catch)
--- try(socket:connect(host.ip, port.number))
+-- try(socket:connect(host, port))
 -- result = try(socket:receive_lines(1))
 -- try(socket:send(result))
 function new_try(handler)
@@ -329,9 +329,10 @@ function bind(addr, port)
 -- This method puts a socket in a state ready for communication. It takes as
 -- arguments a host descriptor (a host table, IP address, or hostname), a port
 -- descriptor (a port table or number), and optionally a protocol. If given, the
--- protocol must be one of
--- <code>"tcp"</code>, <code>"udp"</code> or <code>"ssl"</code>;
--- <code>"tcp"</code> is the default.
+-- protocol must be one of <code>"tcp"</code>, <code>"udp"</code> or
+-- <code>"ssl"</code>. The default value for the protocol is
+-- <code>port.protocol</code> if <code>port</code> is a port table, otherwise
+-- <code>"tcp"</code>.
 --
 -- If <code>host</code> is a host table, it must contain at least one of the
 -- keys <code>addr</code> or <code>targetname</code>. If <code>targetname</code>
@@ -367,7 +368,7 @@ function bind(addr, port)
 -- @return Error code (if status is false).
 -- @see new_socket
 -- @usage
--- local status, err = socket:connect(host.ip, port, "udp")
+-- local status, err = socket:connect(host, port)
 -- if not status then
 --     return string.format("Can't connect: %s", err)
 -- end