mirror of
https://github.com/lunarmodules/luasocket.git
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174 lines
5.0 KiB
HTML
174 lines
5.0 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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<title>LuaSocket: Network support for the Lua language</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 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="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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<!-- stream ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
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<h2 id=stream>Streaming with Callbacks</h2>
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<p>
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HTTP and FTP transfers sometimes involve large amounts of information.
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Sometimes an application needs to generate outgoing data in real time,
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or needs to process incoming information as it is being received. To
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address these problems, LuaSocket allows HTTP message bodies and FTP
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file contents to be received or sent through the callback mechanism
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outlined below.
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</p>
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<p>
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Instead of returning the entire contents of a FTP file or HTTP message
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body as strings to the Lua application, the library allows the user to
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provide a <em>receive callback</em> that will be called with successive
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chunks of data, as the data becomes available. Conversely, the <em>send
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callbacks</em> should be used when data needed by LuaSocket
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is generated incrementally by the application.
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</p>
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<!-- tohostname +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
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<p class=name id=receive_cb>
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<b>receive_cb(</b>chunk, err<b>)</b>
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</p>
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<p class=description>
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The callback provided by the user will be repeatedly called by the
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library whenever new data is available. Each time it is called, the
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callback receives successive chunks of downloaded data.
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</p>
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<p class=parameters>
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<tt>Chunk</tt> contains the current chunk of data.
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When the transmission is over, the function is called with an
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empty string (i.e. <tt>""</tt>) as the <tt>chunk</tt>. If an error occurs, the
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function receives <tt>nil</tt> as <tt>chunk</tt> and an error message as
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<tt>err</tt>.
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</p>
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<p class=return>
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The callback can abort transmission by returning
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<tt>nil</tt> as its first return value. In that case, it can also return
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an error message. Any non-<tt>nil</tt> return value proceeds with the
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transmission.
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</p>
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<pre class=example>
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-- The implementation of socket.callback.receive_concat
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function Public.receive_concat(concat)
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concat = concat or socket.concat.create()
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local callback = function(chunk, err)
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-- if not finished, add chunk
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if chunk and chunk ~= "" then
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concat:addstring(chunk)
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return 1
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end
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end
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return callback, concat
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end
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</pre>
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<!-- send_cb ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
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<p class=name>
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<b>send_cb()</b>
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</p>
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<p class=description>
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The callback provided by the user will be repeatedly called whenever the
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library needs more data to be sent.
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</p>
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<p class=return>
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Each time the callback is called, it
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should return the next part of the information the library is expecting,
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followed by the total number of bytes to be sent.
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The callback can abort
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the process at any time by returning <tt>nil</tt> followed by an
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optional error message.
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</p>
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<p class=note>
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Note: The need for the second return value comes from the fact that, with
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the HTTP protocol for instance, the library needs to know in advance the
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total number of bytes that will be sent.
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</p>
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<pre class=example>
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-- The implementation of socket.callback.send_file
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function Public.send_file(file)
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local callback
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-- if successfull, return the callback that reads from the file
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if file then
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-- get total size
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local size = file:seek("end")
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-- go back to start of file
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file:seek("set")
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callback = function()
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-- send next block of data
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local chunk = file:read(Public.BLOCKSIZE)
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if not chunk then file:close() end
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return chunk, size
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end
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-- else, return a callback that just aborts the transfer
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else
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callback = function()
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-- just abort
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return nil, "unable to open file"
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end
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end
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return callback, file
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end
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</pre>
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<!-- footer +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
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<div class=footer>
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<hr>
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<center>
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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#down">download</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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<p>
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<small>
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Last modified by Diego Nehab on <br>
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Sat Aug 9 01:00:41 PDT 2003
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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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