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417 lines
13 KiB
HTML
417 lines
13 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
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"http://www.w3.org/TR/html4/strict.dtd">
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<html>
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<head>
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<meta name="description" content="LuaSocket: The UDP support">
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<meta name="keywords" content="Lua, LuaSocket, Socket, UDP, Library, Network, Support">
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<title>LuaSocket: UDP support</title>
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<link rel="stylesheet" href="reference.css" type="text/css">
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</head>
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<body>
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<!-- header ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
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<div class=header>
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<hr>
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<center>
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<table summary="LuaSocket logo">
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<tr><td align=center><a href="http://www.lua.org">
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<img width=128 height=128 border=0 alt="LuaSocket" src="luasocket.png">
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</a></td></tr>
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<tr><td align=center valign=top>Network support for the Lua language
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</td></tr>
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</table>
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<p class=bar>
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<a href="home.html">home</a> ·
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<a href="home.html#download">download</a> ·
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<a href="installation.html">installation</a> ·
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<a href="introduction.html">introduction</a> ·
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<a href="reference.html">reference</a>
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</p>
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</center>
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<hr>
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</div>
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<!-- udp ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
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<h2 id=udp>UDP</h2>
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<!-- socket.udp ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
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<p class="name" id="socket.udp">
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socket.<b>udp()</b>
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</p>
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<p class="description">
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Creates and returns an unconnected UDP object. Unconnected objects support the
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<a href="#sendto"><tt>sendto</tt></a>,
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<a href="#receive"><tt>receive</tt></a>,
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<a href="#receivefrom"><tt>receivefrom</tt></a>,
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<a href="#getsockname"><tt>getsockname</tt></a>,
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<a href="#setoption"><tt>setoption</tt></a>,
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<a href="#settimeout"><tt>settimeout</tt></a>,
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<a href="#setpeername"><tt>setpeername</tt></a>,
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<a href="#setsockname"><tt>setsockname</tt></a>, and
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<a href="#close"><tt>close</tt></a>.
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The <a href="#setpeername"><tt>setpeername</tt></a>
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is used to connect the object.
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</p>
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<p class="return">
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In case of success, a new unconnected UDP object
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returned. In case of error, <b><tt>nil</tt></b> is returned, followed by
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an error message.
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</p>
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<!-- close +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
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<p class="name" id="close">
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connected:<b>close()</b><br>
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unconnected:<b>close()</b>
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</p>
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<p class="description">
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Closes a UDP object. The internal socket
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used by the object is closed and the local address to which the
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object was bound is made available to other applications. No
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further operations (except for further calls to the <tt>close</tt>
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method) are allowed on a closed socket.
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</p>
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<p class="note">
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Note: It is important to close all used sockets
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once they are not needed, since, in many systems, each socket uses
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a file descriptor, which are limited system resources.
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Garbage-collected objects are automatically closed before
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destruction, though.
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</p>
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<!-- getpeername +++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
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<p class="name" id="getpeername">
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connected:<b>getpeername()</b>
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</p>
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<p class="description">
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Retrieves information about the peer
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associated with a connected UDP object.
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</p>
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<p class="return">
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Returns the IP address and port number of the peer.
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</p>
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<p class="note">
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Note: It makes no sense to call this method on unconnected objects.
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</p>
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<!-- getsockname +++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
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<p class="name" id="getsockname">
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connected:<b>getsockname()</b><br>
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unconnected:<b>getsockname()</b>
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</p>
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<p class="description">
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Returns the local address information associated to the object.
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</p>
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<p class="return">
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The method returns a string with local IP
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address and a number with the port. In case of error, the method
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returns <b><tt>nil</tt></b>.
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</p>
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<p class="note">
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Note: UDP sockets are not bound to any address
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until the <a href="#setsockname"><tt>setsockname</tt></a> or the
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<a href="#sendto"><tt>sendto</tt></a> method is called for the
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first time (in which case it is bound to an ephemeral port and the
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wild-card address).
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</p>
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<!-- receive +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
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<p class="name" id="receive">
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connected:<b>receive(</b>[size]<b>)</b><br>
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unconnected:<b>receive(</b>[size]<b>)</b>
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</p>
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<p class="description">
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Receives a datagram from the UDP object. If
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the UDP object is connected, only datagrams coming from the peer
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are accepted. Otherwise, the returned datagram can come from any
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host.
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</p>
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<p class="parameters">
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The optional <tt>size</tt> parameter
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specifies the maximum size of the datagram to be retrieved. If
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there are more than <tt>size</tt> bytes available in the datagram,
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the excess bytes are discarded. If there are less then
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<tt>size</tt> bytes available in the current datagram, the
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available bytes are returned. If <tt>size</tt> is omitted, the
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maximum datagram size is used (which is currently limited by the
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implementation to 8192 bytes).
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</p>
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<p class="return">
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In case of success, the method returns the
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received datagram. In case of timeout, the method returns
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<b><tt>nil</tt></b> followed by the string '<tt>timeout</tt>'.
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</p>
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<!-- receivefrom +++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
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<p class="name" id="receivefrom">
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unconnected:<b>receivefrom(</b>[size]<b>)</b>
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</p>
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<p class="description">
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Works exactly as the <a href="#receive"><tt>receive</tt></a>
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method, except it returns the IP
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address and port as extra return values (and is therefore slightly less
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efficient).
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</p>
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<!-- send ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
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<p class="name" id="send">
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connected:<b>send(</b>datagram<b>)</b>
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</p>
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<p class="description">
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Sends a datagram to the UDP peer of a connected object.
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</p>
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<p class="parameters">
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<tt>Datagram</tt> is a string with the datagram contents.
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The maximum datagram size for UDP is 64K minus IP layer overhead.
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However datagrams larger than the link layer packet size will be
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fragmented, which may deteriorate performance and/or reliability.
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</p>
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<p class="return">
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If successful, the method returns 1. In case of
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error, the method returns <b><tt>nil</tt></b> followed by an error message.
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</p>
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<p class="note">
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Note: In UDP, the <tt>send</tt> method never blocks
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and the only way it can fail is if the underlying transport layer
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refuses to send a message to the specified address (i.e. no
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interface accepts the address).
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</p>
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<!-- sendto ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
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<p class="name" id="sendto">
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unconnected:<b>sendto(</b>datagram, ip, port<b>)</b>
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</p>
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<p class="description">
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Sends a datagram to the specified IP address and port number.
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</p>
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<p class="parameters">
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<tt>Datagram</tt> is a string with the
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datagram contents.
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The maximum datagram size for UDP is 64K minus IP layer overhead.
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However datagrams larger than the link layer packet size will be
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fragmented, which may deteriorate performance and/or reliability.
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<tt>Ip</tt> is the IP address of the recipient.
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Host names are <em>not</em> allowed for performance reasons.
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<tt>Port</tt> is the port number at the recipient.
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</p>
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<p class="return">
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If successful, the method returns 1. In case of
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error, the method returns <b><tt>nil</tt></b> followed by an error message.
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</p>
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<p class="note">
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Note: In UDP, the <tt>send</tt> method never blocks
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and the only way it can fail is if the underlying transport layer
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refuses to send a message to the specified address (i.e. no
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interface accepts the address).
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</p>
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<!-- setpeername +++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
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<p class="name" id="setpeername">
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connected:<b>setpeername(</b>'*'<b>)</b><br>
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unconnected:<b>setpeername(</b>address, port<b>)</b>
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</p>
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<p class="description">
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Changes the peer of a UDP object. This
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method turns an unconnected UDP object into a connected UDP
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object or vice versa.
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</p>
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<p class="description">
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For connected objects, outgoing datagrams
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will be sent to the specified peer, and datagrams received from
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other peers will be discarded by the OS. Connected UDP objects must
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use the <a href="#send"><tt>send</tt></a> and
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<a href="#receive"><tt>receive</tt></a> methods instead of
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<a href="#sendto"><tt>sendto</tt></a> and
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<a href="#receivefrom"><tt>receivefrom</tt></a>.
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</p>
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<p class="parameters">
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<tt>Address</tt> can be an IP address or a
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host name. <tt>Port</tt> is the port number. If <tt>address</tt> is
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'<tt>*</tt>' and the object is connected, the peer association is
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removed and the object becomes an unconnected object again. In that
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case, the <tt>port</tt> argument is ignored.
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</p>
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<p class="return">
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In case of error the method returns
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<b><tt>nil</tt></b> followed by an error message. In case of success, the
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method returns 1.
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</p>
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<p class="note">
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Note: Since the address of the peer does not have
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to be passed to and from the OS, the use of connected UDP objects
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is recommended when the same peer is used for several transmissions
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and can result in up to 30% performance gains.
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</p>
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<!-- setsockname +++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
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<p class="name" id="setsockname">
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unconnected:<b>setsockname(</b>address, port<b>)</b>
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</p>
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<p class="description">
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Binds the UDP object to a local address.
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</p>
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<p class="parameters">
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<tt>Address</tt> can be an IP address or a
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host name. If <tt>address</tt> is '<tt>*</tt>' the system binds to
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all local interfaces using the constant <tt>INADDR_ANY</tt>. If
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<tt>port</tt> is 0, the system chooses an ephemeral port.
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</p>
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<p class="return">
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If successful, the method returns 1. In case of
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error, the method returns <b><tt>nil</tt></b> followed by an error
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message.
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</p>
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<p class="note">
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Note: This method can only be called before any
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datagram is sent through the UDP object, and only once. Otherwise,
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the system automatically binds the object to all local interfaces
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and chooses an ephemeral port as soon as the first datagram is
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sent. After the local address is set, either automatically by the
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system or explicitly by <tt>setsockname</tt>, it cannot be
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changed.
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</p>
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<!-- setoption +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
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<p class="name" id="setoption">
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connected:<b>setoption(</b>option [, value]<b>)</b><br>
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unconnected:<b>setoption(</b>option [, value]<b>)</b>
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</p>
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<p class="description">
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Sets options for the UDP object. Options are
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only needed by low-level or time-critical applications. You should
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only modify an option if you are sure you need it.</p>
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<p class="parameters"><tt>Option</tt> is a string with the option
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name, and <tt>value</tt> depends on the option being set:
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</p>
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<ul>
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<li>'<tt>dontroute</tt>': Setting this option to <tt>true</tt>
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indicates that outgoing messages should bypass the standard routing
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facilities;</li>
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<li>'<tt>broadcast</tt>': Setting this option to <tt>true</tt>
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requests permission to send broadcast datagrams on the
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socket.</li>
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</ul>
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<p class="return">
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The method returns 1 in case of success, or
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<b><tt>nil</tt></b> followed by an error message otherwise.
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</p>
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<p class="note">
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Note: The descriptions above come from the man
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pages.
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</p>
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<!-- settimeout +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
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<p class="name" id="settimeout">
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connected:<b>settimeout(</b>value<b>)</b><br>
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unconnected:<b>settimeout(</b>value<b>)</b>
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</p>
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<p class="description">
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Changes the timeout values for the object. By default, the
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<a href="#receive"><tt>receive</tt></a> and
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<a href="#receivefrom"><tt>receivefrom</tt></a>
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operations are blocking. That is, any call to the methods will block
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indefinitely, until data arrives. The <tt>settimeout</tt> function defines
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a limit on the amount of time the functions can block. When a timeout is
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set and the specified amount of time has elapsed, the affected methods
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give up and fail with an error code.
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</p>
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<p class="parameters">
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The amount of time to wait is specified as
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the <tt>value</tt> parameter, in seconds. The <b><tt>nil</tt></b> timeout
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<tt>value</tt> allows operations to block indefinitely. Negative
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timeout values have the same effect.
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</p>
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<p class="note">
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Note: In UDP, the <a href="#send"><tt>send</tt></a>
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and <a href="#sentdo"><tt>sendto</tt></a> methods never block (the
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datagram is just passed to the OS and the call returns
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immediately). Therefore, the <tt>settimeout</tt> method has no
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effect on them.
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</p>
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<p class="note">
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Note: The old <tt>timeout</tt> method is
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deprecated. The name has been changed for sake of uniformity, since
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all other method names already contained verbs making their
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imperative nature obvious.
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</p>
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<!-- footer ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
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<div class=footer>
|
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<hr>
|
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<center>
|
|
<p class=bar>
|
|
<a href="home.html">home</a> ·
|
|
<a href="home.html#download">download</a> ·
|
|
<a href="installation.html">installation</a> ·
|
|
<a href="introduction.html">introduction</a> ·
|
|
<a href="reference.html">reference</a>
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</p>
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<p>
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<small>
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Last modified by Diego Nehab on <br>
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Mon Nov 21 01:58:15 EST 2005
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</small>
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</p>
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</center>
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</div>
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</body>
|
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</html>
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