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TCP sockets with coroutines

local loop = require'socketloop'

A socket loop enables coroutine-based asynchronous I/O programming model for TCP sockets. The concept is similar to Copas, the API and the implementation are different. Supports both symmetric and asymmetric coroutines.


loop.wrap(socket) -> asocket wrap a TCP socket to an async socket
loop.connect(ip, port) -> asocket make an async TCP connection
loop.newthread(handler, arg) create a thread for one connection
loop.current() -> thread current thread
loop.suspend() suspend current thread
loop.resume(thread, arg) resume a suspended thread
loop.newserver(ip, port, handler) -> skt dispatch inbound connections to a function
loop.start([timeout]) start the loop
loop.stop() stop the loop (if started)
loop.step([timeout]) -> true|false dispatch pending reads and writes
loop.coro -> loop coro-based loop

loop.wrap(socket) -> asocket

Wrap a TCP socket into an asynchronous socket with the same API as the original, which btw is kept as asocket.socket.

Being asynchronous means that if each socket is used from its own coroutine, different sockets won't block each other waiting for reads and writes, as long as the loop is doing the dispatching. The asynchronous methods are: connect(), accept(), receive(), send(), close().

An async socket should only be used inside a loop thread.

loop.connect(ip, port [,local_ip] [,local_port]) -> asocket

Make a TCP connection and return an async socket.

loop.newthread(handler, arg) -> thread

Create and resume a thead (either a coroutine or a coro thread). The thread is suspended and control returns to the caller as soon as:

  • an async socket method is called,
  • loop.suspend() is called,
  • the thread finishes.

loop.current() -> thread

Return the current thread (either a coroutine or a coro thread).


Suspend the current thread. To resume a suspended thread, call loop.resume() from another thread.

loop.resume(thread, arg)

Resume a previously suspended thread. Only resume threads that were previously suspended by calling loop.suspend(). Resuming a thread that is suspended in an async call is undefined behavior.

loop.newserver(ip, port, handler)

Create a TCP socket and start accepting connections on it, and call handler(client_skt) on a separate coroutine for each accepted connection.


Start dispatching reads and writes continuously in a loop. The loop should be started only if there's at least one thread suspended in an async socket call.


Stop the dispatch loop (if started).

loop.step([timeout]) -> true|false

Dispatch currently pending reads and writes to their respective threads.

loop = require'socketloop'.coro

An alternative loop that dispatches to symmetric coroutines instead of Lua coroutines.


local loop = require'socketloop'
local http = require'socket.http'

local function getpage(url)
   local t = {}
   local ok, code, headers = http.request{
      url = url,
      sink = ltn12.sink.table(t),
      create = function()
         return loop.wrap(socket.try(socket.tcp()))
   assert(ok, code)
   return table.concat(t), headers, code

   local body = getpage''
   print('got ' .. #body .. ' bytes')


Last updated: 22 months ago | Edit on GitHub

Pkg type:Lua+ffi
Version: r3-3-gdc064f3
Last commit:
License: Public Domain
Requires: +glue  +socket  +luajit 
Required by: none