socket server

steve64

Is it possible to write a Lua TCP socket server managing multiple concurrent Lua clients with the current LuaRT modules?
I saw the example under the documentation for the "select" fucntion but it does not seem updated, for instance it refers to the missing "listen" function...

In particular, I would like each client to keep its own connection and send multiple messages to the server during its session. Should I use coroutines for this?

Samir

Thank you for the report. The example was not updated since a few versions of LuaRT.

Here is a more updated example to use multiple connected clients on a server :

-- Multi-connection Server example
local net = require "net"

-- create the server listening Socket
local server = net.Socket("127.0.0.1", 5000)

-- array of clients Sockets
local sockets = {server}
server.disconnected = false

if server:bind() then
	print("Server running on 127.0.0.1:5000")
else
	error("Network error : cannot create the server Socket")
end

while true do
	if net.select(sockets) == false then
		error("Network error : "..net.error)
		break
	end
	
	local alive_sockets = {}
	for client in each(sockets) do
		-- check for readability 
		if client.canread then
			if client == server then
				if server.canread then
					-- check for new connection
					local newclient = server:accept()
					print(newclient.ip.." has connected")
					sockets[#sockets+1] = newclient
				end
			else
				local data = client:recv()
				if data == false then
					print(client.ip.." has disconnected")
					client.disconnected = true
        else
          print(client.ip..": "..tostring(data))
				end
			end			
		end
		-- check for error
		if client.failed then
			if client == server then
				error("fatal network error with server")
			else
				print(client.ip.." has encountered a fatal network error")
				client.disconnected = true
			end
		end
		if not client.disconnected then
			alive_sockets[#alive_sockets+1] = client
		end
	end
	-- keep only connected clients
	sockets = alive_sockets
end

Samir

You can test it easily by launching this command on a console :

luart -e "s = require('net').Socket('127.0.0.1', 5000); s:connect(); s:send('Hello !')"

steve64

Is it possible to change TCP_NODELAY, e.g. setting to zero ?

Samir

By default TCP_NODELAY is unmodified (on Windows, it's already set to FALSE during socket creation).
But it may be useful to add a Socket property to enabled/disable it.

Thank you for the feedback.

Samir

Update : Socket.nodelay property has been implemented

steve64

Many thanks.
Is there any way to intercept when a Lua console mode program (in general, but especially a TCP server)
is exited (e.g. by Ctrl-C or killing it)? I mean something like a "on exit" callback?

Samir

steve64 I mean something like a "on exit" callback?

It's already implemented for next LuaRT version 👍️

steve64

Samir When do you plan to deliver next official LuaRT version?

Samir

I'm working on a last bug.
I hope to release next version in the next few days

steve64

What is the sendall() method actually doing?
I'm trying to use the net module for a lightweight RPC application with a local socket.
Requests are quite small. Can sendall() guarantee that each client request is sent to the server in a single packet?

Samir

Socket.send try to send the data but may fail to send entire data and returns the number of bytes sent.

Socket.sendall ensures that the entire data are effectively sent before returning

steve64

The server.wlua example program is interesting, but I'm wondering how much time is left for processing GUI events in case of heavy client traffic.
ui.update() is called only in the outer loop, and the inner loop could not terminate often enough.
It is helpful to put ui.update() also in the inner loop to give more chance to the GUI events, or is there any drawback/constraint?
Another option could be to put a maximum iterations number in the inner loop, so that after N client messages the loop will exit and a GUI update would be done anyway.

What's your opinion?

Besides GUI responsiveness, there's another point in the example.
Is there any need for reducing the sockets and/or alive_sockets lists when a client disconnects ?

Samir

This problem is common to the asynchronous programming concept in all langages, not only Lua.

You can adapt what you want in term of priority, either GUI or Sockets, by using the manually ui.update() function.

For the Socket disconnection, it's better to delete the socket from the list to indicate the garage collector that the ressources can be freed.