luasocket/docs/socket.html

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<!-- socket +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<h2 id="socket">The socket namespace</h2>

<p>
The <tt>socket</tt> namespace contains the core functionality of LuaSocket.
</p>

<p>
To obtain the <tt>socket</tt> namespace, run:
</p>

<pre class="example">
-- loads the socket module
local socket = require("socket")
</pre>

<!-- headers.canonic ++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class="name" id="headers.canonic">
socket.headers.<b>canonic</b></p>

<p> The <tt>socket.headers.canonic</tt> table
is used by the HTTP and SMTP modules to translate from
lowercase field names back into their canonic
capitalization. When a lowercase field name exists as a key
in this table, the associated value is substituted in
whenever the field name is sent out.
</p>

<p>
You can obtain the <tt>headers</tt> namespace if case run-time
modifications are required by running:
</p>

<pre class="example">
-- loads the headers module
local headers = require("headers")
</pre>


<!-- bind ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class="name" id="bind">
socket.<b>bind(</b>address, port [, backlog]<b>)</b>
</p>

<p class="description">
This function is a shortcut that creates and returns a TCP server object
bound to a local <tt>address</tt> and <tt>port</tt>, ready to
accept client connections. Optionally,
user can also specify the <tt>backlog</tt> argument to the
<a href="tcp.html#listen"><tt>listen</tt></a> method (defaults to 32).
</p>

<p class="note">
Note: The server object returned will have the option "<tt>reuseaddr</tt>"
set to <tt><b>true</b></tt>.
</p>

<!-- connect ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class="name" id="connect">
socket.<b>connect[46](</b>address, port [, locaddr] [, locport] [, family]<b>)</b>
</p>

<p class="description">
This function is a shortcut that creates and returns a TCP client object
connected to a remote <tt>address</tt> at a given <tt>port</tt>. Optionally,
the user can also specify the local address and port to bind
(<tt>locaddr</tt> and <tt>locport</tt>), or restrict the socket family
to "<tt>inet</tt>" or "<tt>inet6</tt>".
Without specifying <tt>family</tt> to <tt>connect</tt>, whether a tcp or tcp6
connection is created depends on your system configuration. Two variations
of connect are defined as simple helper functions that restrict the
<tt>family</tt>, <tt>socket.connect4</tt> and <tt>socket.connect6</tt>.
</p>

<!-- debug ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class="name" id="debug">
socket.<b>_DEBUG</b>
</p>

<p class="description">
This constant is set to <tt><b>true</b></tt> if the library was compiled
with debug support.
</p>

<!-- datagramsize +++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class="name" id="datagramsize">
socket.<b>_DATAGRAMSIZE</b>
</p>

<p class="description">
Default datagram size used by calls to
<a href="udp.html#receive"><tt>receive</tt></a> and
<a href="udp.html#receivefrom"><tt>receivefrom</tt></a>.
(Unless changed in compile time, the value is 8192.)
</p>

<!-- get time +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class="name" id="gettime">
socket.<b>gettime()</b>
</p>

<p class="description">
Returns the UNIX time in seconds. You should subtract the values returned by this function
to get meaningful values.
</p>

<pre class="example">
t = socket.gettime()
-- do stuff
print(socket.gettime() - t .. " seconds elapsed")
</pre>

<!-- newtry +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class="name" id="newtry">
socket.<b>newtry(</b>finalizer<b>)</b>
</p>

<p class="description">
Creates and returns a <em>clean</em>
<a href="#try"><tt>try</tt></a>
function that allows for cleanup before the exception
is  raised.
This implements the ideas described in
<a href="https://github.com/lunarmodules/luasocket/blob/master/ltn013.md">
LTN012, Using finalized exceptions</a>.
</p>

<p class="parameters">
<tt>Finalizer</tt> is a function that will be called before
<tt>try</tt> throws the exception.
</p>

<p class="return">
The function returns your customized <tt>try</tt> function.
</p>

<p class="note">
Note: This idea saved a <em>lot</em> of work with the
implementation of protocols in LuaSocket:
</p>

<pre class="example">
foo = socket.protect(function()
    -- connect somewhere
    local c = socket.try(socket.connect("somewhere", 42))
    -- create a try function that closes 'c' on error
    local try = socket.newtry(function() c:close() end)
    -- do everything reassured c will be closed
    try(c:send("hello there?\r\n"))
    local answer = try(c:receive())
    ...
    try(c:send("good bye\r\n"))
    c:close()
end)
</pre>


<!-- protect +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class="name" id="protect">
socket.<b>protect(</b>func<b>)</b>
</p>

<p class="description">
Converts a function that throws exceptions into a safe function. This
function only catches exceptions thrown by the <a href="#try"><tt>try</tt></a>
and <a href="#newtry"><tt>newtry</tt></a> functions. It does not catch normal
Lua errors.
This implements the ideas described in
<a href="https://github.com/lunarmodules/luasocket/blob/master/ltn013.md">
LTN012, Using finalized exceptions</a>.
</p>

<p class="parameters">
<tt>Func</tt> is a function that calls
<a href="#try"><tt>try</tt></a> (or <tt>assert</tt>, or <tt>error</tt>)
to throw exceptions.
</p>

<p class="return">
Returns an equivalent function that instead of throwing exceptions in case of
a failed <a href="#try"><tt>try</tt></a> call, returns <tt><b>nil</b></tt>
followed by an error message.
</p>

<!-- select +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class="name" id="select">
socket.<b>select(</b>recvt, sendt [, timeout]<b>)</b>
</p>

<p class="description">
Waits for a number of sockets to change status.
</p>

<p class="parameters">
<tt>Recvt</tt> is an array with the sockets to test for characters
available for reading. Sockets in the <tt>sendt</tt> array are watched to
see if it is OK to immediately write on them.  <tt>Timeout</tt> is the
maximum amount of time (in seconds) to wait for a change in status.  A
<tt><b>nil</b></tt>, negative or omitted <tt>timeout</tt> value allows the
function to block indefinitely. <tt>Recvt</tt> and <tt>sendt</tt> can also
be empty tables or <tt><b>nil</b></tt>. Non-socket values (or values with
non-numeric indices) in the arrays will be silently ignored.
</p>

<p class="return"> The function returns a list with the sockets ready for
reading, a list with the sockets ready for writing and an error message.
The error message is "<tt>timeout</tt>" if a timeout
condition was met, "<tt>select failed</tt>" if the call
to <tt>select</tt> failed, and
<tt><b>nil</b></tt> otherwise. The returned tables are
doubly keyed both by integers and also by the sockets
themselves, to simplify the test if a specific socket has
changed status.
</p>

<p class="note">
<b>Note:</b> <tt>select</tt> can monitor a limited number
of sockets, as defined by the constant <a href="#setsize">
<tt>socket._SETSIZE</tt></a>. This
number may be as high as 1024 or as low as 64 by default,
depending on the system. It is usually possible to change this
at compile time. Invoking <tt>select</tt> with a larger
number of sockets will raise an error.
</p>

<p class="note">
<b>Important note</b>: a known bug in WinSock causes <tt>select</tt> to fail
on non-blocking TCP sockets. The function may return a socket as
writable even though the socket is <em>not</em> ready for sending.
</p>

<p class="note">
<b>Another important note</b>: calling select with a server socket in the receive parameter before a call to accept does <em>not</em> guarantee
<a href="tcp.html#accept"><tt>accept</tt></a> will return immediately.
Use the <a href="tcp.html#settimeout"><tt>settimeout</tt></a>
method or <tt>accept</tt> might block forever.
</p>

<p class="note">
<b>Yet another note</b>: If you close a socket and pass
it to <tt>select</tt>, it will be ignored.
</p>

<p class="note">
<b>Using select with non-socket objects</b>: Any object that implements <tt>getfd</tt> and <tt>dirty</tt> can be used with <tt>select</tt>, allowing objects from other libraries to be used within a <tt>socket.select</tt> driven loop.
</p>

<!-- setsize ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class="name" id="setsize">
socket.<b>_SETSIZE</b>
</p>

<p class="description">
The maximum number of sockets that the <a
href="#select"><tt>select</tt></a> function can handle.
</p>


<!-- sink ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class="name" id="sink">
socket.<b>sink(</b>mode, socket<b>)</b>
</p>

<p class="description">
Creates an
<a href="http://lua-users.org/wiki/FiltersSourcesAndSinks">LTN12</a>
sink from a stream socket object.
</p>

<p class="parameters">
<tt>Mode</tt> defines the behavior of the sink. The following
options are available:
</p>
<ul>
<li> <tt>"http-chunked"</tt>: sends data through socket after applying the
<em>chunked transfer coding</em>, closing the socket when done;</li>
<li> <tt>"close-when-done"</tt>: sends all received data through the
socket, closing the socket when done;</li>
<li> <tt>"keep-open"</tt>: sends all received data through the
socket, leaving it open when done.</li>
</ul>
<p>
<tt>Socket</tt> is the stream socket object used to send the data.
</p>

<p class="return">
The function returns a sink with the appropriate behavior.
</p>

<!-- skip ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class="name" id="skip">
socket.<b>skip(</b>d [, ret<sub>1</sub>, ret<sub>2</sub> ...  ret<sub>N</sub>]<b>)</b>
</p>

<p class="description">
Drops a number of arguments and returns the remaining.
</p>

<p class="parameters">
<tt>D</tt> is the number of arguments to drop. <tt>Ret<sub>1</sub></tt> to
<tt>ret<sub>N</sub></tt> are the arguments.
</p>

<p class="return">
The function returns <tt>ret<sub>d+1</sub></tt> to <tt>ret<sub>N</sub></tt>.
</p>

<p class="note">
Note: This function is useful to avoid creation of dummy variables:
</p>

<pre class="example">
-- get the status code and separator from SMTP server reply
local code, sep = socket.skip(2, string.find(line, "^(%d%d%d)(.?)"))
</pre>

<!-- sleep ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class="name" id="sleep">
socket.<b>sleep(</b>time<b>)</b>
</p>

<p class="description">
Freezes the program execution during a given amount of time.
</p>

<p class="parameters">
<tt>Time</tt> is the number of seconds to sleep for. If
<tt>time</tt> is negative, the function returns immediately.
</p>

<!-- source +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class="name" id="source">
socket.<b>source(</b>mode, socket [, length]<b>)</b>
</p>

<p class="description">
Creates an
<a href="http://lua-users.org/wiki/FiltersSourcesAndSinks">LTN12</a>
source from a stream socket object.
</p>

<p class="parameters">
<tt>Mode</tt> defines the behavior of the source. The following
options are available:
</p>
<ul>
<li> <tt>"http-chunked"</tt>: receives data from socket and removes the
<em>chunked transfer coding</em> before returning the data;</li>
<li> <tt>"by-length"</tt>: receives a fixed number of bytes from the
socket. This mode requires the extra argument <tt>length</tt>;</li>
<li> <tt>"until-closed"</tt>: receives data from a socket until the other
side closes the connection.</li>
</ul>
<p>
<tt>Socket</tt> is the stream socket object used to receive the data.
</p>

<p class="return">
The function returns a source with the appropriate behavior.
</p>

<!-- socketinvalid ++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class="name" id="socketinvalid">
socket.<b>_SOCKETINVALID</b>
</p>

<p class="description">
The OS value for an invalid socket. This can be used with <a href="tcp.html#getfd">
<tt>tcp:getfd</tt></a> and <a href="tcp.html#setfd"><tt>tcp:setfd</tt></a> methods.
</p>

<!-- try ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class="name" id="try">
socket.<b>try(</b>ret<sub>1</sub> [, ret<sub>2</sub> ... ret<sub>N</sub>]<b>)</b>
</p>

<p class="description">
Throws an exception in case <tt>ret<sub>1</sub></tt> is falsy, using
<tt>ret<sub>2</sub></tt> as the error message. The exception is supposed to be caught
by a <a href="#protect"><tt>protect</tt></a>ed function only.
This implements the ideas described in
<a href="https://github.com/lunarmodules/luasocket/blob/master/ltn013.md">
LTN012, Using finalized exceptions</a>.
</p>

<p class="parameters">
<tt>Ret<sub>1</sub></tt> to <tt>ret<sub>N</sub></tt> can be arbitrary
arguments, but are usually the return values of a function call
nested with <tt>try</tt>.
</p>

<p class="return">
The function returns <tt>ret</tt><sub>1</sub> to <tt>ret</tt><sub>N</sub> if
<tt>ret</tt><sub>1</sub> is not <tt><b>nil</b></tt> or <tt><b>false</b></tt>.
Otherwise, it calls <tt>error</tt> passing <tt>ret</tt><sub>2</sub> wrapped
in a table with metatable used by <a href="#protect"><tt>protect</tt></a> to
distinguish exceptions from runtime errors.
</p>

<pre class="example">
-- connects or throws an exception with the appropriate error message
c = socket.try(socket.connect("localhost", 80))
</pre>

<!-- version ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class="name" id="version">
socket.<b>_VERSION</b>
</p>

<p class="description">
This constant has a string describing the current LuaSocket version.
</p>

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<p>
<small>
Last modified by Diego Nehab on <br>
Thu Apr 20 00:25:54 EDT 2006
</small>
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