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<!-- ltn12 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<h2 id=ltn12>LTN12</h2> 

<p> The <tt>ltn12</tt> namespace implements the ideas described in
<a href="http://lua-users.org/wiki/FiltersSourcesAndSinks">
LTN012, Filters sources and sinks</a>. This manual simply describes the
functions. Please refer to the LTN for a deeper explanation of the
functionality provided by this module.
</p>

<p> 
To obtain the <tt>ltn12</tt> namespace, run:
</p>

<pre class=example>
-- loads the LTN21 module
local ltn12 = require("ltn12")
</pre>

<!-- filters ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<h3 id="filter">Filters</h3>

<!-- chain ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class=name id="filter.chain">
ltn12.filter.<b>chain(</b>filter<sub>1</sub>, filter<sub>2</sub> 
[, ... filter<sub>N</sub>]<b>)</b>
</p>

<p class=description>
Returns a filter that passes all data it receives through each of a
series of given filters. 
</p>

<p class=parameters>
<tt>Filter<sub>1</sub></tt> to <tt>filter<sub>N</sub></tt> are simple
filters. 
</p>

<p class=return>
The function returns the chained filter.
</p>

<p class=note>
The nesting of filters can be arbitrary. For instance, the useless filter
below doesn't do anything but return the data that was passed to it,
unaltered.
</p>

<pre class=example>
-- load required modules
local ltn12 = require("ltn12")
local mime = require("mime")

-- create a silly identity filter
id = ltn12.filter.chain(
  mime.encode("quoted-printable"),
  mime.encode("base64"),
  mime.decode("base64"),
  mime.decode("quoted-printable")
)
</pre>

<!-- cycle ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class=name id="filter.cycle">
ltn12.filter.<b>cycle(</b>low [, ctx, extra]<b>)</b>
</p>

<p class=description>
Returns a high-level filter that cycles though a low-level filter by
passing it each chunk and updating a context between calls. 
</p>

<p class=parameters>
<tt>Low</tt> is the low-level filter to be cycled, 
<tt>ctx</tt> is the initial context and <tt>extra</tt> is any extra
argument the low-level filter might take.
</p>

<p class=return>
The function returns the high-level filter. 
</p>

<pre class=example>
-- load the ltn12 module
local ltn12 = require("ltn12")

-- the base64 mime filter factory
encodet['base64'] = function()
    return ltn12.filter.cycle(b64, "")
end
</pre>

<!-- pumps ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<h3 id="pump">Pumps</h3>

<!-- all ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class=name id="pump.all">
ltn12.pump.<b>all(</b>source, sink<b>)</b>
</p>

<p class=description>
Pumps <em>all</em> data from a <tt>source</tt> to a <tt>sink</tt>. 
</p>

<p class=return>
If successful, the function returns a value that evaluates to
<b><tt>true</tt></b>. In case
of error, the function returns a <b><tt>false</tt></b> value, followed by an error message.
</p>

<!-- step +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class=name id="pump.step">
ltn12.pump.<b>step(</b>source, sink<b>)</b>
</p>

<p class=description>
Pumps <em>one</em> chunk of data from a <tt>source</tt> to a <tt>sink</tt>. 
</p>

<p class=return>
If successful, the function returns a value that evaluates to
<b><tt>true</tt></b>. In case
of error, the function returns a <b><tt>false</tt></b> value, followed by an error message.
</p>

<!-- sinks ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<h3 id="sink">Sinks</h3>

<!-- chain ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class=name id="sink.chain">
ltn12.sink.<b>chain(</b>filter, sink<b>)</b>
</p>

<p class=description>
Creates and returns a new sink that passes data through a <tt>filter</tt> before sending it to a given <tt>sink</tt>. 
</p>

<!-- error ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class=name id="sink.error">
ltn12.sink.<b>error(</b>message<b>)</b>
</p>

<p class=description>
Creates and returns a sink that aborts transmission with the error
<tt>message</tt>.
</p>

<!-- file +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class=name id="sink.file">
ltn12.sink.<b>file(</b>handle, message<b>)</b>
</p>

<p class=description>
Creates a sink that sends data to a file. 
</p>

<p class=parameters>
<tt>Handle</tt> is a file handle. If <tt>handle</tt> is <tt><b>nil</b></tt>, 
<tt>message</tt> should give the reason for failure. 
</p>

<p class=return>
The function returns a sink that sends all data to the given <tt>handle</tt>
and closes the file when done, or a sink that aborts the transmission with
the error <tt>message</tt>
</p>

<p class=note>
In the following example, notice how the prototype is designed to 
fit nicely with the <tt>io.open</tt> function.
</p>

<pre class=example>
-- load the ltn12 module
local ltn12 = require("ltn12")

-- copy a file
ltn12.pump.all(
  ltn12.source.file(io.open("original.png")),
  ltn12.sink.file(io.open("copy.png"))
)
</pre>

<!-- null +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class=name id="sink.null">
ltn12.sink.<b>null()</b>
</p>

<p class=description>
Returns a sink that ignores all data it receives. 
</p>

<!-- simplify +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class=name id="sink.simplify">
ltn12.sink.<b>simplify(</b>sink<b>)</b>
</p>

<p class=description>
Creates and returns a simple sink given a fancy <tt>sink</tt>. 
</p>

<!-- table ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class=name id="sink.table">
ltn12.sink.<b>table(</b>[table]<b>)</b>
</p>

<p class=description>
Creates a sink that stores all chunks in a table. The chunks can later be
efficiently concatenated into a single string.
</p>

<p class=parameters>
<tt>Table</tt> is used to hold the chunks. If
<tt><b>nil</b></tt>, the function creates its own table. 
</p>

<p class=return>
The function returns the sink and the table used to store the chunks. 
</p>

<pre class=example>
-- load needed modules
local http = require("socket.http")
local ltn12 = require("ltn12")

-- a simplified http.get function
function http.get(u)
  local t = {}
  local respt = request{
    url = u,
    sink = ltn12.sink.table(t)
  }
  return table.concat(t), respt.headers, respt.code
end
</pre>

<!-- sinks ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<h3 id="source">Sources</h3>

<!-- cat ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class=name id="source.cat">
ltn12.source.<b>cat(</b>source<sub>1</sub> [, source<sub>2</sub>, ...,
source<sub>N</sub>]<b>)</b>
</p>

<p class=description>
Creates a new source that produces the concatenation of the data produced
by a number of sources. 
</p>

<p class=parameters>
<tt>Source<sub>1</sub></tt> to <tt>source<sub>N</sub></tt> are the original
sources. 
</p>

<p class=return>
The function returns the new source.
</p>

<!-- chain ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class=name id="source.chain">
ltn12.source.<b>chain(</b>source, filter<b>)</b>
</p>

<p class=description>
Creates a new <tt>source</tt> that passes data through a <tt>filter</tt> 
before returning it. 
</p>

<p class=return>
The function returns the new source.
</p>

<!-- empty ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class=name id="source.empty">
ltn12.source.<b>empty()</b>
</p>

<p class=description>
Creates and returns an empty source. 
</p>

<!-- error ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class=name id="source.error">
ltn12.source.<b>error(</b>message<b>)</b>
</p>

<p class=description>
Creates and returns a source that aborts transmission with the error
<tt>message</tt>.
</p>

<!-- file +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class=name id="source.file">
ltn12.source.<b>file(</b>handle, message<b>)</b>
</p>

<p class=description>
Creates a source that produces the contents of a file. 
</p>

<p class=parameters>
<tt>Handle</tt> is a file handle. If <tt>handle</tt> is <tt><b>nil</b></tt>, 
<tt>message</tt> should give the reason for failure. 
</p>

<p class=return>
The function returns a source that reads chunks of data from 
given <tt>handle</tt> and returns it to the user,
closing the file when done, or a source that aborts the transmission with
the error <tt>message</tt>
</p>

<p class=note>
In the following example, notice how the prototype is designed to 
fit nicely with the <tt>io.open</tt> function.
</p>

<pre class=example>
-- load the ltn12 module
local ltn12 = require("ltn12")

-- copy a file
ltn12.pump.all(
  ltn12.source.file(io.open("original.png")),
  ltn12.sink.file(io.open("copy.png"))
)
</pre>

<!-- simplify +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class=name id="source.simplify">
ltn12.source.<b>simplify(</b>source<b>)</b>
</p>

<p class=description>
Creates and returns a simple source given a fancy <tt>source</tt>. 
</p>

<!-- string +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

<p class=name id="source.string">
ltn12.source.<b>string(</b>string<b>)</b>
</p>

<p class=description>
Creates and returns a source that produces the contents of a
<tt>string</tt>, chunk by chunk. 
</p>

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<small>
Last modified by Diego Nehab on <br>
Thu Apr 20 00:25:41 EDT 2006
</small>
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