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<!-- udp ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<h2 id=udp>UDP</h2>

<!-- socket.udp ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

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

<p class="description">
Creates and returns an unconnected UDP object. Unconnected objects support the
<a href="#sendto"><tt>sendto</tt></a>,
<a href="#receive"><tt>receive</tt></a>,
<a href="#receivefrom"><tt>receivefrom</tt></a>,
<a href="#getsockname"><tt>getsockname</tt></a>,
<a href="#setoption"><tt>setoption</tt></a>,
<a href="#settimeout"><tt>settimeout</tt></a>,
<a href="#setpeername"><tt>setpeername</tt></a>,
<a href="#setsockname"><tt>setsockname</tt></a>, and
<a href="#close"><tt>close</tt></a>.
The <a href="#setpeername"><tt>setpeername</tt></a>
is used to connect the object.
</p>

<p class="return">
In case of success, a new unconnected UDP object
returned. In case of error, <b><tt>nil</tt></b> is returned, followed by
an error message.
</p>

<!-- close +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class="name" id="close">
connected:<b>close()</b><br>
unconnected:<b>close()</b>
</p>

<p class="description">
Closes a UDP object. The internal socket
used by the object is closed and the local address to which the
object was bound is made available to other applications. No
further operations (except for further calls to the <tt>close</tt>
method) are allowed on a closed socket.
</p>

<p class="note">
Note: It is important to close all used sockets
once they are not needed, since, in many systems, each socket uses
a file descriptor, which are limited system resources.
Garbage-collected objects are automatically closed before
destruction, though.
</p>

<!-- getpeername +++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class="name" id="getpeername">
connected:<b>getpeername()</b>
</p>

<p class="description">
Retrieves information about the peer
associated with a connected UDP object.
</p>

<p class="return">
Returns the IP address and port number of the peer.
</p>

<p class="note">
Note: It makes no sense to call this method on unconnected objects.
</p>

<!-- getsockname +++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class="name" id="getsockname">
connected:<b>getsockname()</b><br>
unconnected:<b>getsockname()</b>
</p>

<p class="description">
Returns the local address information associated to the object.
</p>

<p class="return">
The method returns a string with local IP
address and a number with the port. In case of error, the method
returns <b><tt>nil</tt></b>.
</p>

<p class="note">
Note: UDP sockets are not bound to any address
until the <a href="#setsockname"><tt>setsockname</tt></a> or the
<a href="#sendto"><tt>sendto</tt></a> method is called for the
first time (in which case it is bound to an ephemeral port and the
wild-card address).
</p>

<!-- receive +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class="name" id="receive">
connected:<b>receive(</b>[size]<b>)</b><br>
unconnected:<b>receive(</b>[size]<b>)</b>
</p>

<p class="description">
Receives a datagram from the UDP object. If
the UDP object is connected, only datagrams coming from the peer
are accepted. Otherwise, the returned datagram can come from any
host.
</p>

<p class="parameters">
The optional <tt>size</tt> parameter
specifies the maximum size of the datagram to be retrieved. If
there are more than <tt>size</tt> bytes available in the datagram,
the excess bytes are discarded. If there are less then
<tt>size</tt> bytes available in the current datagram, the
available bytes are returned. If <tt>size</tt> is omitted, the
maximum datagram size is used (which is currently limited by the
implementation to 8192 bytes).
</p>

<p class="return">
In case of success, the method returns the
received datagram. In case of timeout, the method returns
<b><tt>nil</tt></b> followed by the string '<tt>timeout</tt>'.
</p>

<!-- receivefrom +++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class="name" id="receivefrom">
unconnected:<b>receivefrom(</b>[size]<b>)</b>
</p>

<p class="description">
Works exactly as the <a href="#receive"><tt>receive</tt></a>
method, except it returns the IP
address and port as extra return values (and is therefore slightly less
efficient).
</p>

<!-- send ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class="name" id="send">
connected:<b>send(</b>datagram<b>)</b>
</p>

<p class="description">
Sends a datagram to the UDP peer of a connected object.
</p>

<p class="parameters">
<tt>Datagram</tt> is a string with the datagram contents.
The maximum datagram size for UDP is 64K minus IP layer overhead.
However datagrams larger than the link layer packet size will be
fragmented, which may deteriorate performance and/or reliability.
</p>

<p class="return">
If successful, the method returns 1. In case of
error, the method returns <b><tt>nil</tt></b> followed by an error message.
</p>

<p class="note">
Note: In UDP, the <tt>send</tt> method never blocks
and the only way it can fail is if the underlying transport layer
refuses to send a message to the specified address (i.e. no
interface accepts the address).
</p>

<!-- sendto ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class="name" id="sendto">
unconnected:<b>sendto(</b>datagram, ip, port<b>)</b>
</p>

<p class="description">
Sends a datagram to the specified IP address and port number.
</p>

<p class="parameters">
<tt>Datagram</tt> is a string with the
datagram contents.
The maximum datagram size for UDP is 64K minus IP layer overhead.
However datagrams larger than the link layer packet size will be
fragmented, which may deteriorate performance and/or reliability.
<tt>Ip</tt> is the IP address of the recipient.
Host names are <em>not</em> allowed for performance reasons.

<tt>Port</tt> is the port number at the recipient.
</p>

<p class="return">
If successful, the method returns 1. In case of
error, the method returns <b><tt>nil</tt></b> followed by an error message.
</p>

<p class="note">
Note: In UDP, the <tt>send</tt> method never blocks
and the only way it can fail is if the underlying transport layer
refuses to send a message to the specified address (i.e. no
interface accepts the address).
</p>

<!-- setpeername +++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class="name" id="setpeername">
connected:<b>setpeername(</b>'*'<b>)</b><br>
unconnected:<b>setpeername(</b>address, port<b>)</b>
</p>

<p class="description">
Changes the peer of a UDP object. This
method turns an unconnected UDP object into a connected UDP
object or vice versa.
</p>

<p class="description">
For connected objects, outgoing datagrams
will be sent to the specified peer, and datagrams received from
other peers will be discarded by the OS. Connected UDP objects must
use the <a href="#send"><tt>send</tt></a> and
<a href="#receive"><tt>receive</tt></a> methods instead of
<a href="#sendto"><tt>sendto</tt></a> and
<a href="#receivefrom"><tt>receivefrom</tt></a>.
</p>

<p class="parameters">
<tt>Address</tt> can be an IP address or a
host name. <tt>Port</tt> is the port number. If <tt>address</tt> is
'<tt>*</tt>' and the object is connected, the peer association is
removed and the object becomes an unconnected object again. In that
case, the <tt>port</tt> argument is ignored.
</p>

<p class="return">
In case of error the method returns
<b><tt>nil</tt></b> followed by an error message. In case of success, the
method returns 1.
</p>

<p class="note">
Note: Since the address of the peer does not have
to be passed to and from the OS, the use of connected UDP objects
is recommended when the same peer is used for several transmissions
and can result in up to 30% performance gains.
</p>

<!-- setsockname +++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class="name" id="setsockname">
unconnected:<b>setsockname(</b>address, port<b>)</b>
</p>

<p class="description">
Binds the UDP object to a local address.
</p>

<p class="parameters">
<tt>Address</tt> can be an IP address or a
host name. If <tt>address</tt> is '<tt>*</tt>' the system binds to
all local interfaces using the constant <tt>INADDR_ANY</tt>. If
<tt>port</tt> is 0, the system chooses an ephemeral port.
</p>

<p class="return">
If successful, the method returns 1. In case of
error, the method returns <b><tt>nil</tt></b> followed by an error
message.
</p>

<p class="note">
Note: This method can only be called before any
datagram is sent through the UDP object, and only once. Otherwise,
the system automatically binds the object to all local interfaces
and chooses an ephemeral port as soon as the first datagram is
sent. After the local address is set, either automatically by the
system or explicitly by <tt>setsockname</tt>, it cannot be
changed.
</p>

<!-- setoption +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class="name" id="setoption">
connected:<b>setoption(</b>option [, value]<b>)</b><br>
unconnected:<b>setoption(</b>option [, value]<b>)</b>
</p>

<p class="description">
Sets options for the UDP object. Options are
only needed by low-level or time-critical applications. You should
only modify an option if you are sure you need it.</p>
<p class="parameters"><tt>Option</tt> is a string with the option
name, and <tt>value</tt> depends on the option being set:
</p>

<ul>
<li>'<tt>dontroute</tt>': Setting this option to <tt>true</tt>
indicates that outgoing messages should bypass the standard routing
facilities;</li>
<li>'<tt>broadcast</tt>': Setting this option to <tt>true</tt>
requests permission to send broadcast datagrams on the
socket.</li>
</ul>

<p class="return">
The method returns 1 in case of success, or
<b><tt>nil</tt></b> followed by an error message otherwise.
</p>

<p class="note">
Note: The descriptions above come from the man
pages.
</p>

<!-- settimeout +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class="name" id="settimeout">
connected:<b>settimeout(</b>value<b>)</b><br>
unconnected:<b>settimeout(</b>value<b>)</b>
</p>

<p class="description">
Changes the timeout values for the object.  By default, the
<a href="#receive"><tt>receive</tt></a> and
<a href="#receivefrom"><tt>receivefrom</tt></a>
operations are blocking. That is, any call to the methods will block
indefinitely, until data arrives.  The <tt>settimeout</tt> function defines
a limit on the amount of time the functions can block. When a timeout is
set and the specified amount of time has elapsed, the affected methods
give up and fail with an error code.
</p>

<p class="parameters">
The amount of time to wait is specified as
the <tt>value</tt> parameter, in seconds. The <b><tt>nil</tt></b> timeout
<tt>value</tt> allows operations to block indefinitely. Negative
timeout values have the same effect.
</p>

<p class="note">
Note: In UDP, the <a href="#send"><tt>send</tt></a>
and <a href="#sentdo"><tt>sendto</tt></a> methods never block (the
datagram is just passed to the OS and the call returns
immediately). Therefore, the <tt>settimeout</tt> method has no
effect on them.
</p>

<p class="note">
Note: The old <tt>timeout</tt> method is
deprecated. The name has been changed for sake of uniformity, since
all other method names already contained verbs making their
imperative nature obvious.
</p>

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<p>
<small>
Last modified by Diego Nehab on <br>
Thu Apr 20 00:26:01 EDT 2006
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author	Eric Wing <ewing . public \|-at-\| gmail . com>
date	Sat, 30 Aug 2008 08:46:39 -0700
parents	4b915342e2a8
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