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<title>Copas - Coroutine Oriented Portable Asynchronous Services for Lua</title>

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<div id="product_name"><big><strong>Copas</strong></big></div>

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<h1>Copas</h1>

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<li><strong>Manual</strong>

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<li><a href="manual.html#install">Installing</a></li>

<li><a href="manual.html#introduction">Introduction</a></li>

<li><a href="manual.html#why">Why use Copas?</a></li>

<li><a href="manual.html#using">Using Copas</a></li>

<li><a href="manual.html#udp">UDP support</a></li>

<li><a href="manual.html#tasks">Adding tasks</a></li>

<li><a href="manual.html#timers">Creating timers</a></li>

<li><a href="manual.html#ssl">Ssl support</a></li>

<li><a href="manual.html#highlevel">http(s), ftp & smtp</a></li>

<li><a href="manual.html#control">Controlling Copas</a></li>

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<h2><a name="install"></a>Installing</h2>

<p>You can install Copas using <a href="http://www.luarocks.org">LuaRocks</a>:</p>

<pre class="example">

luarocks install copas

<p>Note: LuaSec is not automatically installed as a dependency. If you want to use ssl with Copas,

you need to manually install LuaSec as well.</p>

<h2><a name="introduction"></a>Introduction to Copas</h2>

Copas is a dispatcher that can help a lot in the creation of servers based on

<a href="http://www.cs.princeton.edu/~diego/professional/luasocket/">LuaSocket</a>.

Here we present a quick introduction to Copas and how to implement a server with it.

Assuming you know how to implement the desired server protocol, the first thing you have

to do in order to create a Copas based server is create a server socket to receive the

client connections. To do this you have to bind a host and a port using LuaSocket:

<pre class="example">

server = socket.bind(host, port)

<p>Then you have to create a handler function that implements the server protocol.

The handler function will be called with a socket for each client connection

and you can use <code>copas.send()</code> and <code>copas.receive()</code> on that socket to

exchange data with the client.</p>

<p>For example, a simple echo handler would be:</p>

<pre class="example">

function echoHandler(skt)

while true do

local data = copas.receive(skt)

if data == "quit" then

break

end

copas.send(skt, data)

end

end

<p>You may alternatively use <code>copas.wrap()</code> to let your code more close to a standard

LuaSocket use:</p>

<pre class="example">

function echoHandler(skt)

skt = copas.wrap(skt)

while true do

local data = skt:receive()

if data == "quit" then

break

end

skt:send(data)

end

end

To register the server socket with Copas and associate it with the corresponding

handler we do:

<pre class="example">

copas.addserver(server, echoHandler)

<p>Finally, to start Copas and all the registered servers we just call:</p>

<pre class="example">

copas.loop()

<p>As long as every handler uses Copas's <code>send</code> and <code>receive</code>,

simultaneous connections will be handled transparently by Copas for every registered

server.</p>

Since Copas is coroutine based, using it within a Lua <code>pcall</code> or

<code>xpcall</code> context does not work with Lua 5.1 yielding. If you need to use

any of those functions in your handler we strongly suggest using

<a href="http://keplerproject.github.com/coxpcall/">coxpcall</a>, a coroutine safe

version of the Lua 5.1 protected calls. For an example of this usage please check Xavante.

<h2><a name="why"></a>Why use Copas?</h2>

For those who already have a server implemented, here is an explanation of why and

how to migrate to Copas. In a typical LuaSocket server usually there is a dispatcher

loop like the one below:

<pre class="example">

server = socket.bind(host, port)

while true do

skt = server:accept()

handle(skt)

end

<p>Here <code>handle</code> is a function that implements the server protocol using LuaSocket's

socket functions:</p>

<pre class="example">

function handle(skt)

...

-- gets some data from the client - "the request"

reqdata = skt:receive(pattern)

...

-- sends some data to the client - "the response"

skt:send(respdata)

...

end

The problem with that approach is that the dispatcher loop is doing a busy wait

and can handle just one connection at a time. To solve the busy waiting we can

use LuaSocket's <code>socket.select()</code>, like in:</p>

<pre class="example">

server = socket.bind(host, port)

reading = {server}

while true do

input = socket.select(reading)

skt = input:accept()

handle(skt)

end

While this helps our CPU usage, the server is still accepting only one client

connection at a time. To handle more than one client the server must be able to

multitask, and the solution usually involves some kind of threads.</p>

<p>The dispatcher loop then becomes something like:</p>

<pre class="example">

server = socket.bind(host, port)

reading = {server}

while true do

input = socket.select(reading)

skt = input:accept()

newthread(handle(skt))

end

where <code>newthread</code> is able to create a new thread that executes

independently the handler function.</p>

The use of threads in the new loop solves the multitasking problem but may

create another. Some platforms does not offer multithreading or maybe you

don't want to use threads at all.

If that is the case, using Lua's coroutines may help a lot, and that's

exactly what Copas does. Copas implements the dispatcher loop using coroutines

so the handlers can multitask without the use of threads.</p>

<h2><a name="using"></a>Using Copas with an existing server</h2>

If you already have a running server using some dispatcher like the previous

example, migrating to Copas is quite simple, usually consisting of just three

steps.

First each server socket and its corresponding handler function have to be registered

with Copas:</p>

<pre class="example">

server = socket.bind(host, port)

copas.addserver(server, handle)

<p>Secondly the server handler has to be adapted to use Copas. One solution

is to use Copas <code>send</code> and <code>receive</code> functions to receive

and send data to the client:</p>

<pre class="example">

function handle(skt)

...

-- gets some data from the client - "the request"

reqdata = copas.receive(skt, pattern)

...

-- sends some data to the client - "the response"

copas.send(skt, respdata)

...

end

<p>The other alternative is to wrap the socket in a Copas socket. This

allows your handler code to remain basically the same:</p>

<pre class="example">

function handle(skt)

-- this line may suffice for your handler to work with Copas

skt = copas.wrap(skt) -- or... skip this line and wrap `handle` using copas.handler()

-- now skt behaves like a LuaSocket socket but uses Copas'

...

-- gets some data from the client - "the request"

reqdata = skt:receive(pattern)

...

-- sends some data to the client - "the response"

skt:send(respdata)

...

end

<p>Finally, to run the dispatcher loop you just call:</p>

<pre class="example">

copas.loop()

<p>During the loop Copas' dispatcher accepts connections from clients and

automatically calls the corresponding handler functions.</p>

<h2><a name="udp"></a>Using UDP servers</h2>

<p>Copas may also be used for UDP servers. Here is an example;</p>

<pre class="example">

local port = 51034

local server = socket.udp()

server:setsockname("*",port)

function handler(skt)

skt = copas.wrap(skt)

print("UDP connection handler")

while true do

local s, err

print("receiving...")

s, err = skt:receive(2048)

if not s then

print("Receive error: ", err)

return

end

print("Received data, bytes:" , #s)

end

end

copas.addserver(server, handler, 1)

copas.loop()

<p>For UDP sockets the <code>receivefrom()</code> and <code>sendto()</code>

methods are available, both for copas and when the socket is wrapped. These

methods cannot be used on TCP sockets.</p>

<p><strong>IMPORTANT:</strong> UDP sockets do not have the notion of master and client sockets, so where a handler function can close the client socket for a TCP connection, a handler should never close a UDP socket, because the socket is the same as the server socket, hence closing it destroys the server.</p>

<p><strong>NOTE:</strong> When using the <code>copas.receive([size])</code> method

on a UDP socket, the <code>size</code> parameter is NOT optional as with regular

luasocket UDP sockets. This limitation is removed when the socket is wrapped

(it then defaults to 8192, the max UDP datagram size luasocket supports).</p>

<h2><a name="tasks"></a>Adding tasks</h2>

<p>Additional threads may be added to the scheduler, as long as they use the Copas <code>send</code>, <code>receive</code> or <code>sleep</code> methods. Below an example of a thread being added to create an outgoing TCP connection using Copas;</p>

<pre class="example">

local socket = require("socket")

local copas = require("copas")

local host = "127.0.0.1"

local port = 10000

local skt = socket.connect(host, port)

skt:settimeout(0) -- important: make it non-blocking

copas.addthread(function()

while true do

print("receiving...")

local resp = copas.receive(skt, 6)

print("received:", resp or "nil")

if resp and resp:sub(1,4) == "quit" then

skt:close()

break

end

end

end)

copas.loop()

<p>The example connects, echoes whatever it receives and exits upon receiving 'quit'. For an

example passing arguments to a task, see the async http example below.</p>

<h2><a name="timers"></a>Creating timers</h2>

<p>Timers can be created using the <code>addthread</code> method with the <code>sleep</code> method.

Below an example of a thread being added to create and used as a timer;</p>

<pre class="example">

local copas = require("copas")

copas.addthread(function()

print("This will print immediately, upon adding the thread. So before the loop starts")

while true do

copas.sleep(1) -- 1 second interval

print("Hello there!")

end

end)

print("We're starting!")

copas.loop()

<p>The example simply prints a message once every second.</p>

<h2><a name="ssl"></a>Ssl support</h2>

<p>LuaSec is transparently integrated in the Copas scheduler (though must be installed separately when using LuaRocks).</p>

Here's an example for an incoming connection in a server scenario;

<pre class="example">

function handler(skt)

skt = copas.wrap(skt):dohandshake(sslparams)

-- skt = copas.wrap(skt, sslparams):dohandshake() -- would be identical

while true do

-- perform the regular reading/writing ops on skt

end

end

A simpler handler would wrap the handler function to do the wrapping and

handshake before the handler gets called;

<pre class="example">

function handle(skt)

-- by now `skt` is copas wrapped, and has its handshake already completed

while true do

-- perform the regular reading/writing ops on skt

end

end

handle = copas.handler(handle, sslparams) -- wraps the handler to auto wrap and handshake

Here's an example for an outgoing request;

<pre class="example">

copas.addthread(function()

local skt = copas.wrap(socket.tcp(), sslparams)

skt:connect(host, port) -- connecting will also perform the handshake on a wrapped socket

while true do

-- perform the regular reading/writing ops on skt

end

end

<h2><a name="highlevel"></a>High level requests</h2>

For creating high level requests; http(s), ftp or smtp versions of the

methods are available that handle them async. As opposed to the original

LuaSocket and LuaSec implementations.

Below an example that schedules a number of http requests, then starts the Copas

loop to execute them. The loop exits when it's done.

<pre class="example">

local copas = require("copas")

local asynchttp = require("copas.http").request

local list = {

"http://www.google.com",

"http://www.microsoft.com",

"http://www.apple.com",

"http://www.facebook.com",

"http://www.yahoo.com",

}

local handler = function(host)

res, err = asynchttp(host)

print("Host done: "..host)

end

for _, host in ipairs(list) do copas.addthread(handler, host) end

copas.loop()

<h2><a name="control"></a>Controlling Copas</h2>

If you do not want copas to simply enter an infinite loop (maybe you have to

respond to events from other sources, such as an user interface), you should

have your own loop and just call <code>copas.step()</code> at each iteration of

the loop:

<pre class="example">

while condition do

copas.step()

-- processing for other events from your system here

end

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