new gist: simpletcpserver.lua

simpletcpserver.lua

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+--[[
+-- Simplest possible tcp echo server.
+-- ... Well, that's a lie. It's the simplest possible TCP server that can handle multiple clients at the same time, that I was able to write.
+]]--
+
+local socket = require("socket")
+local server = socket.tcp()
+-- The low timeout time is so no one client blocks any other
+-- I can see that if the server needs to receive or send a lot of data, then those routines will become blocked. I _could_ use something better than coroutines to make this, but then it wouldn't have been so simple, now would it? :þ
+server:settimeout(0.005, "t")
+
+hostname = "localhost"
+port = 12346
+
+server:bind(hostname, port)
+server:listen(128)
+
+local clients = {}
+
+co_newClient = coroutine.create(function ()
+	while true do
+		local nC, err = server:accept()
+		if err then
+			if err == "timeout" then
+				coroutine.yield()
+			else
+				error("ERROR: "..err)
+			end
+		end
+		if nC then
+			-- Individual clients, however, need a higher timeout if we want to be able to give them time to connect to the tcp socket and actually send something.
+			nC:settimeout(10)
+			-- Insert the new client into the client table
+			table.insert(clients, nC)
+			nC = nil
+			coroutine.yield()
+		end
+	end
+end)
+co_selectClient = coroutine.create(function ()
+	while true do
+		-- For more information, see https://lunarmodules.github.io/luasocket/socket.html#select
+		r, w, e = socket.select(clients, nil, 0.005)
+		if e then
+			-- Timeout = No clients, keep waiting for clients
+			if e == "timeout" then
+				coroutine.resume(co_newClient)
+			else
+				error("ERROR: "..e)
+			end
+		end
+		coroutine.yield()
+	end
+end)
+
+co_receiveFromClient = coroutine.create(function ()
+	while true do
+		for _, client in ipairs(r) do
+			local message, err, partial = client:receive("*l")
+				if err then
+					-- Maybe timeout should remove the client from the table too?
+					if err == "timeout" then
+						coroutine.yield()
+					elseif err == "closed" then
+						table.remove(clients, _)
+						coroutine. yield()
+					end
+				end
+				if message then
+					if message == "goodbye" then
+						client:send("GOODBYE\n")
+						client:close()
+						table.remove(clients, _)
+						coroutine.yield()
+					else
+						client:send("Echo: "..message.."\n")
+						coroutine.yield()
+					end
+				end
+				if partial then
+					coroutine.yield()
+				end
+		end
+		coroutine.yield()
+	end
+end)
+
+while true do
+	coroutine.resume(co_newClient)
+	coroutine.resume(co_selectClient)
+	coroutine.resume(co_receiveFromClient)
+end