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<title>Ocamlnet 2 Reference Manual : Netchannels</title>
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<center><h1>Module <a href="type_Netchannels.html">Netchannels</a></h1></center>
<br>
<pre><span class="keyword">module</span> Netchannels: <code class="code">sig</code> <a href="Netchannels.html">..</a> <code class="code">end</code></pre>Object-oriented I/O: Basic types and classes
<p>
<b>Contents</b>
<p>
<ul>
<li><a href="Netchannels.html#types"><i>Types</i></a></li>
<li><a href="Netchannels.html#input"><i>Input channels</i></a></li>
<li><a href="Netchannels.html#output"><i>Output channels</i></a></li>
<li><a href="Netchannels.html#delegation"><i>Delegation classes</i></a></li>
<li><a href="Netchannels.html#lifting"><i>Lifting channels</i></a></li>
<li><a href="Netchannels.html#descriptors"><i>Channels over descriptors</i></a></li>
<li><a href="Netchannels.html#transactional"><i>Transactional channels</i></a></li>
<li><a href="Netchannels.html#filters"><i>Pipes and Filters</i></a>
<ul>
<li><a href="Netchannels.html#filters_notes"><i>Notes, Examples</i></a></li>
</ul>
</li>
</ul>
The tutorial has been moved to <a href="Netchannels_tut.html"><code class="code">Netchannels_tut</code></a>.<br>
<hr width="100%">
<br>
<a name="types"></a>
<h1>Types</h1><br>
<br>
There are three levels of class types for channels:<ul>
<li><code class="code">rec_in_channel</code> and <code class="code">rec_out_channel</code>: Primitive, but standardized level</li>
<li><code class="code">raw_in_channel</code> and <code class="code">raw_out_channel</code>: Unix level</li>
<li><code class="code">in_obj_channel</code> and <code class="code">out_obj_channel</code>: Application level</li>
</ul>
The "rec" level has been recently introduced to improve interoperability
with other libraries (e.g. camomile). The idea is to standardize the
real core methods of I/O, so they have the same meaning in all libraries.
Read
"<a href="http://www.ocaml-programming.de/rec/IO-Classes.html">Basic I/O class types</a>"
for more.
<p>
The "raw" level represents the level of Unix file descriptors.
<p>
The application level is what should be used in programs. In addition
to the "raw" level one can find a number of convenience methods,
e.g. <code class="code">input_line</code> to read a line from the channel. The downside is that
these methods usually work only for blocking I/O.
<p>
One can lower the level by coercion, e.g. to turn an <code class="code">in_obj_channel</code>
into a <code class="code">rec_in_channel</code>, apply the function
<p>
<code class="code">(fun ch -> (ch : in_obj_channel :> rec_in_channel))</code>
<p>
To higher the level, apply <code class="code">lift_in</code> or <code class="code">lift_out</code>, defined below.<br>
<br>
<b>Interface changes:</b> Since ocamlnet-0.98, the semantics of
the methods <code class="code">input</code> and <code class="code">output</code> has slightly changed. When the end
of the channel is reached, <code class="code">input</code> raises now <code class="code">End_of_file</code>. In previous
releases of ocamlnet, the value 0 was returned. When the channel cannot
process data, but is in non-blocking mode, both methods now return the
value 0. In previous releases of ocamlnet, the behaviour was not
defined.<br>
<pre><span class="keyword">exception</span> <a name="EXCEPTIONClosed_channel"></a>Closed_channel</pre>
<div class="info">
Raised when channel operations are called when the channel is closed<br>
</div>
<pre><span class="keyword">exception</span> <a name="EXCEPTIONBuffer_underrun"></a>Buffer_underrun</pre>
<div class="info">
Raised by input methods if the internal buffer of the channel is too
empty to read even one byte of data.
This exception is only used by certain implementations of channel
classes.<br>
</div>
<pre><span class="keyword">exception</span> <a name="EXCEPTIONCommand_failure"></a>Command_failure <span class="keyword">of</span> <code class="type">Unix.process_status</code></pre>
<div class="info">
Raised by <code class="code">close_in</code> or <code class="code">close_out</code> if the channel is connected with
another process, and the execution of that process fails.<br>
</div>
<pre><span class="keyword">class type</span> <a name="TYPErec_in_channel"></a><a href="Netchannels.rec_in_channel.html">rec_in_channel</a> = <code class="code">object</code> <a href="Netchannels.rec_in_channel.html">..</a> <code class="code">end</code></pre><div class="info">
Recommended input class type for library interoperability.
</div>
<pre><span class="keyword">class type</span> <a name="TYPEraw_in_channel"></a><a href="Netchannels.raw_in_channel.html">raw_in_channel</a> = <code class="code">object</code> <a href="Netchannels.raw_in_channel.html">..</a> <code class="code">end</code></pre><div class="info">
Basic Unix-level class type for input channels as used by ocamlnet.
</div>
<pre><span class="keyword">class type</span> <a name="TYPErec_out_channel"></a><a href="Netchannels.rec_out_channel.html">rec_out_channel</a> = <code class="code">object</code> <a href="Netchannels.rec_out_channel.html">..</a> <code class="code">end</code></pre><div class="info">
Recommended output class type for library interoperability.
</div>
<pre><span class="keyword">class type</span> <a name="TYPEraw_out_channel"></a><a href="Netchannels.raw_out_channel.html">raw_out_channel</a> = <code class="code">object</code> <a href="Netchannels.raw_out_channel.html">..</a> <code class="code">end</code></pre><div class="info">
Basic Unix-level class type for output channels as used by ocamlnet.
</div>
<pre><span class="keyword">class type</span> <a name="TYPEraw_io_channel"></a><a href="Netchannels.raw_io_channel.html">raw_io_channel</a> = <code class="code">object</code> <a href="Netchannels.raw_io_channel.html">..</a> <code class="code">end</code></pre><div class="info">
A channel supporting both input and output.
</div>
<pre><span class="keyword">class type</span> <a name="TYPEcompl_in_channel"></a><a href="Netchannels.compl_in_channel.html">compl_in_channel</a> = <code class="code">object</code> <a href="Netchannels.compl_in_channel.html">..</a> <code class="code">end</code></pre><div class="info">
Further methods usually supported by ocamlnet channel implementations.
</div>
<pre><span class="keyword">class type</span> <a name="TYPEin_obj_channel"></a><a href="Netchannels.in_obj_channel.html">in_obj_channel</a> = <code class="code">object</code> <a href="Netchannels.in_obj_channel.html">..</a> <code class="code">end</code></pre><div class="info">
The application-level input channel supports raw and complemented methods
</div>
<pre><span class="keyword">class type</span> <a name="TYPEcompl_out_channel"></a><a href="Netchannels.compl_out_channel.html">compl_out_channel</a> = <code class="code">object</code> <a href="Netchannels.compl_out_channel.html">..</a> <code class="code">end</code></pre><div class="info">
Further methods usually supported by ocamlnet channel implementations.
</div>
<pre><span class="keyword">class type</span> <a name="TYPEout_obj_channel"></a><a href="Netchannels.out_obj_channel.html">out_obj_channel</a> = <code class="code">object</code> <a href="Netchannels.out_obj_channel.html">..</a> <code class="code">end</code></pre><div class="info">
The application-level output channel supports raw and complemented methods
</div>
<pre><span class="keyword">class type</span> <a name="TYPEio_obj_channel"></a><a href="Netchannels.io_obj_channel.html">io_obj_channel</a> = <code class="code">object</code> <a href="Netchannels.io_obj_channel.html">..</a> <code class="code">end</code></pre><div class="info">
A channel supporting both input and output.
</div>
<pre><span class="keyword">class type</span> <a name="TYPEtrans_out_obj_channel"></a><a href="Netchannels.trans_out_obj_channel.html">trans_out_obj_channel</a> = <code class="code">object</code> <a href="Netchannels.trans_out_obj_channel.html">..</a> <code class="code">end</code></pre><div class="info">
A transactional output channel has a buffer for uncommitted data.
</div>
<br>
<a name="input"></a>
<h1>Input channels</h1><br>
<pre><span class="keyword">class</span> <a name="TYPEinput_channel"></a><a href="Netchannels.input_channel.html">input_channel</a> : <code class="type">Pervasives.in_channel -> </code><code class="type"><a href="Netchannels.in_obj_channel.html">in_obj_channel</a></code></pre><div class="info">
Creates an input channel from an <code class="code">in_channel</code>, which must be open.
</div>
<pre><span class="keyword">class</span> <a name="TYPEinput_command"></a><a href="Netchannels.input_command.html">input_command</a> : <code class="type">string -> </code><code class="type"><a href="Netchannels.in_obj_channel.html">in_obj_channel</a></code></pre><div class="info">
Runs the command with <code class="code">/bin/sh</code>, and reads the data the command prints
to stdout.
</div>
<pre><span class="keyword">class</span> <a name="TYPEinput_string"></a><a href="Netchannels.input_string.html">input_string</a> : <code class="type">?pos:int -> ?len:int -> string -> </code><code class="type"><a href="Netchannels.in_obj_channel.html">in_obj_channel</a></code></pre><div class="info">
Creates an input channel from a (constant) string.
</div>
<pre><span class="keyword">val</span> <a name="VALcreate_input_netbuffer"></a>create_input_netbuffer : <code class="type"><a href="Netbuffer.html#TYPEt">Netbuffer.t</a> -> <a href="Netchannels.in_obj_channel.html">in_obj_channel</a> * (unit -> unit)</code></pre><div class="info">
Creates an input channel and a shutdown function for a netbuffer.
This is a destructive
implementation: Every time data is read, the octets are taken from the
beginning of the netbuffer, and they are deleted from the netbuffer
(recall that a netbuffer works like a queue of characters).
<p>
Conversely, the user of this class may add new data to the netbuffer
at any time. When the shutdown function is called, the EOF condition
is recorded, and no further data must be added.
<p>
If the netbuffer becomes empty, the input methods raise <code class="code">Buffer_underrun</code>
when the EOF condition has not yet been set, and they raise
<code class="code">End_of_file</code> when the EOF condition has been recorded.<br>
</div>
<pre><span class="keyword">val</span> <a name="VALlexbuf_of_in_obj_channel"></a>lexbuf_of_in_obj_channel : <code class="type"><a href="Netchannels.in_obj_channel.html">in_obj_channel</a> -> Lexing.lexbuf</code></pre><div class="info">
Creates a lexical buffer from an input channel. The input channel
is not closed when the end is reached
<p>
This function does not work for non-blocking channels.<br>
</div>
<pre><span class="keyword">val</span> <a name="VALstring_of_in_obj_channel"></a>string_of_in_obj_channel : <code class="type"><a href="Netchannels.in_obj_channel.html">in_obj_channel</a> -> string</code></pre><div class="info">
Reads from the input channel until EOF and returns the characters
as string. The input channel is not closed.
<p>
This function does not work for non-blocking channels.<br>
</div>
<pre><span class="keyword">val</span> <a name="VALwith_in_obj_channel"></a>with_in_obj_channel : <code class="type">(#<a href="Netchannels.in_obj_channel.html">in_obj_channel</a> as 'a) -> ('a -> 'b) -> 'b</code></pre><div class="info">
<code class="code">with_in_obj_channel ch f</code>:
Computes <code class="code">f ch</code> and closes <code class="code">ch</code>. If an exception happens, the channel is
closed, too.<br>
</div>
<br>
<a name="output"></a>
<h1>Output channels</h1><br>
<pre><span class="keyword">class</span> <a name="TYPEoutput_channel"></a><a href="Netchannels.output_channel.html">output_channel</a> : <code class="type">?onclose:unit -> unit -> Pervasives.out_channel -> </code><code class="type"><a href="Netchannels.out_obj_channel.html">out_obj_channel</a></code></pre><div class="info">
Creates an output channel writing into an <code class="code">out_channel</code>.
</div>
<pre><span class="keyword">class</span> <a name="TYPEoutput_command"></a><a href="Netchannels.output_command.html">output_command</a> : <code class="type">?onclose:unit -> unit -> string -> </code><code class="type"><a href="Netchannels.out_obj_channel.html">out_obj_channel</a></code></pre><div class="info">
Runs the command with <code class="code">/bin/sh</code>, and data written to the channel is
piped to stdin of the command.
</div>
<pre><span class="keyword">class</span> <a name="TYPEoutput_buffer"></a><a href="Netchannels.output_buffer.html">output_buffer</a> : <code class="type">?onclose:unit -> unit -> Buffer.t -> </code><code class="type"><a href="Netchannels.out_obj_channel.html">out_obj_channel</a></code></pre><div class="info">
This output channel writes the data into the passed buffer.
</div>
<pre><span class="keyword">class</span> <a name="TYPEoutput_netbuffer"></a><a href="Netchannels.output_netbuffer.html">output_netbuffer</a> : <code class="type">?onclose:unit -> unit -> <a href="Netbuffer.html#TYPEt">Netbuffer.t</a> -> </code><code class="type"><a href="Netchannels.out_obj_channel.html">out_obj_channel</a></code></pre><div class="info">
This output channel writes the data into the passed netbuffer.
</div>
<pre><span class="keyword">class</span> <a name="TYPEoutput_null"></a><a href="Netchannels.output_null.html">output_null</a> : <code class="type">?onclose:unit -> unit -> unit -> </code><code class="type"><a href="Netchannels.out_obj_channel.html">out_obj_channel</a></code></pre><div class="info">
This output channel discards all written data.
</div>
<pre><span class="keyword">val</span> <a name="VALwith_out_obj_channel"></a>with_out_obj_channel : <code class="type">(#<a href="Netchannels.out_obj_channel.html">out_obj_channel</a> as 'a) -> ('a -> 'b) -> 'b</code></pre><div class="info">
<code class="code">with_out_obj_channel ch f</code>:
Computes <code class="code">f ch</code> and closes <code class="code">ch</code>. If an exception happens, the channel is
closed, too.<br>
</div>
<br>
<a name="delegation"></a>
<h1>Delegation classes</h1><br>
<br>
Delegation classes just forward method calls to an parameter
object, i.e. when method <code class="code">m</code> of the delegation class is called,
the definition of <code class="code">m</code> is just to call the method with the same
name <code class="code">m</code> of the parameter object. This is very useful in order
to redefine methods individually.
<p>
For example, to redefine the method <code class="code">pos_in</code> of an <code class="code">in_obj_channel</code>,
use
<pre><code class="code"> class my_channel = object(self)
inherit in_obj_channel_delegation ...
method pos_in = ...
end
</code></pre>
<p>
As a special feature, the following delegation classes can suppress
the delegation of <code class="code">close_in</code> or <code class="code">close_out</code>, whatever applies.
Just pass <code class="code">close:false</code> to get this effect, e.g.
<pre><code class="code"> class input_channel_don't_close c =
in_obj_channel_delegation ~close:false (new input_channel c)
</code></pre>
This class does not close <code class="code">c : in_channel</code> when the <code class="code">close_in</code>
method is called.<br>
<pre><span class="keyword">class</span> <a name="TYPErec_in_channel_delegation"></a><a href="Netchannels.rec_in_channel_delegation.html">rec_in_channel_delegation</a> : <code class="type">?close:bool -> <a href="Netchannels.rec_in_channel.html">rec_in_channel</a> -> </code><code class="type"><a href="Netchannels.rec_in_channel.html">rec_in_channel</a></code></pre><pre><span class="keyword">class</span> <a name="TYPEraw_in_channel_delegation"></a><a href="Netchannels.raw_in_channel_delegation.html">raw_in_channel_delegation</a> : <code class="type">?close:bool -> <a href="Netchannels.raw_in_channel.html">raw_in_channel</a> -> </code><code class="type"><a href="Netchannels.raw_in_channel.html">raw_in_channel</a></code></pre><pre><span class="keyword">class</span> <a name="TYPEin_obj_channel_delegation"></a><a href="Netchannels.in_obj_channel_delegation.html">in_obj_channel_delegation</a> : <code class="type">?close:bool -> <a href="Netchannels.in_obj_channel.html">in_obj_channel</a> -> </code><code class="type"><a href="Netchannels.in_obj_channel.html">in_obj_channel</a></code></pre><pre><span class="keyword">class</span> <a name="TYPErec_out_channel_delegation"></a><a href="Netchannels.rec_out_channel_delegation.html">rec_out_channel_delegation</a> : <code class="type">?close:bool -> <a href="Netchannels.rec_out_channel.html">rec_out_channel</a> -> </code><code class="type"><a href="Netchannels.rec_out_channel.html">rec_out_channel</a></code></pre><pre><span class="keyword">class</span> <a name="TYPEraw_out_channel_delegation"></a><a href="Netchannels.raw_out_channel_delegation.html">raw_out_channel_delegation</a> : <code class="type">?close:bool -> <a href="Netchannels.raw_out_channel.html">raw_out_channel</a> -> </code><code class="type"><a href="Netchannels.raw_out_channel.html">raw_out_channel</a></code></pre><pre><span class="keyword">class</span> <a name="TYPEout_obj_channel_delegation"></a><a href="Netchannels.out_obj_channel_delegation.html">out_obj_channel_delegation</a> : <code class="type">?close:bool -> <a href="Netchannels.out_obj_channel.html">out_obj_channel</a> -> </code><code class="type"><a href="Netchannels.out_obj_channel.html">out_obj_channel</a></code></pre><br>
<a name="lifting"></a>
<h1>Lifting channels</h1><br>
<br>
The following classes and functions add missing methods to reach
a higher level in the hierarchy of channel class types. For most
uses, the <code class="code">lift_in</code> and <code class="code">lift_out</code> functions work best.<br>
<pre><span class="keyword">val</span> <a name="VALlift_in"></a>lift_in : <code class="type">?eol:string list -><br> ?buffered:bool -><br> ?buffer_size:int -><br> [ `Raw of <a href="Netchannels.raw_in_channel.html">raw_in_channel</a> | `Rec of <a href="Netchannels.rec_in_channel.html">rec_in_channel</a> ] -><br> <a href="Netchannels.in_obj_channel.html">in_obj_channel</a></code></pre><div class="info">
Turns a <code class="code">rec_in_channel</code> or <code class="code">raw_in_channel</code>, depending on the passed
variant, into a full <code class="code">in_obj_channel</code> object. (This is a convenience
function, you can also use the classes below directly.) If you
want to define a class for the lifted object, use
<pre><code class="code"> class lifted_ch ... =
in_obj_channel_delegation (lift_in ...)
</code></pre>
<p>
<br>
</div>
<div class="param_info"><code class="code">eol</code> : The accepted end-of-line delimiters. The method
<code class="code">input_line</code> recognizes any of the passed strings as EOL
delimiters. When more than one delimiter matches, the longest
is taken. Defaults to <code class="code"> ["\n"] </code>. The default cannot be
changed when <code class="code">buffered=false</code> (would raise <code class="code">Invalid_argument</code>).
The delimiter strings must neither be empty, nor longer than
<code class="code">buffer_size</code>.</div>
<div class="param_info"><code class="code">buffered</code> : Whether a buffer is added, by default <b>true</b></div>
<div class="param_info"><code class="code">buffer_size</code> : The size of the buffer, if any, by default 4096</div>
<pre><span class="keyword">val</span> <a name="VALlift_out"></a>lift_out : <code class="type">?buffered:bool -><br> ?buffer_size:int -><br> [ `Raw of <a href="Netchannels.raw_out_channel.html">raw_out_channel</a> | `Rec of <a href="Netchannels.rec_out_channel.html">rec_out_channel</a> ] -><br> <a href="Netchannels.out_obj_channel.html">out_obj_channel</a></code></pre><div class="info">
Turns a <code class="code">rec_out_channel</code> or <code class="code">raw_out_channel</code>, depending on the passed
variant, into a full <code class="code">out_obj_channel</code> object. (This is a convenience
function, you can also use the classes below directly.) If you
want to define a class for the lifted object, use
<pre><code class="code"> class lifted_ch ... =
out_obj_channel_delegation (lift_out ...)
</code></pre>
<p>
<br>
</div>
<div class="param_info"><code class="code">buffered</code> : Whether a buffer is added, by default <b>true</b></div>
<div class="param_info"><code class="code">buffer_size</code> : The size of the buffer, if any, by default 4096</div>
<pre><span class="keyword">class</span> <a name="TYPEaugment_raw_in_channel"></a><span class="keyword">virtual</span> <a href="Netchannels.augment_raw_in_channel.html">augment_raw_in_channel</a> : <code class="type"></code><code class="code">object</code> <a href="Netchannels.augment_raw_in_channel.html">..</a> <code class="code">end</code></pre><div class="info">
This class implements the methods from <code class="code">compl_in_channel</code> by calling
the methods of <code class="code">raw_in_channel</code>.
</div>
<pre><span class="keyword">class</span> <a name="TYPElift_rec_in_channel"></a><a href="Netchannels.lift_rec_in_channel.html">lift_rec_in_channel</a> : <code class="type">?start_pos_in:int -> <a href="Netchannels.rec_in_channel.html">rec_in_channel</a> -> </code><code class="type"><a href="Netchannels.in_obj_channel.html">in_obj_channel</a></code></pre><div class="info">
This class implements <code class="code">pos_in</code> and the methods from <code class="code">compl_in_channel</code>
by calling the methods of <code class="code">rec_in_channel</code>.
</div>
<pre><span class="keyword">class</span> <a name="TYPEaugment_raw_out_channel"></a><span class="keyword">virtual</span> <a href="Netchannels.augment_raw_out_channel.html">augment_raw_out_channel</a> : <code class="type"></code><code class="code">object</code> <a href="Netchannels.augment_raw_out_channel.html">..</a> <code class="code">end</code></pre><div class="info">
This class implements the methods from <code class="code">compl_out_channel</code> by calling
the methods of <code class="code">raw_out_channel</code>.
</div>
<pre><span class="keyword">class</span> <a name="TYPElift_raw_out_channel"></a><a href="Netchannels.lift_raw_out_channel.html">lift_raw_out_channel</a> : <code class="type"><a href="Netchannels.raw_out_channel.html">raw_out_channel</a> -> </code><code class="type"><a href="Netchannels.out_obj_channel.html">out_obj_channel</a></code></pre><div class="info">
This class implements the methods from <code class="code">compl_out_channel</code> by calling
the methods of <code class="code">raw_out_channel</code>.
</div>
<pre><span class="keyword">class</span> <a name="TYPElift_rec_out_channel"></a><a href="Netchannels.lift_rec_out_channel.html">lift_rec_out_channel</a> : <code class="type">?start_pos_out:int -> <a href="Netchannels.rec_out_channel.html">rec_out_channel</a> -> </code><code class="type"><a href="Netchannels.out_obj_channel.html">out_obj_channel</a></code></pre><div class="info">
This class implements <code class="code">pos_out</code> and the methods from <code class="code">compl_out_channel</code>
by calling the methods of <code class="code">rec_out_channel</code>.
</div>
<pre><span class="keyword">type</span> <a name="TYPEinput_result"></a><code class="type"></code>input_result = <code class="type">[ `Data of int | `Separator of string ]</code> </pre>
<div class="info">
This type is for the method <code class="code">enhanced_input</code> of <code class="code">enhanced_raw_in_channel</code>.<ul>
<li><code class="code">`Data n</code> means that <code class="code">n</code> bytes have been copied to the target string</li>
<li><code class="code">`Separator s</code> means that no bytes have been copied, but that an
end-of-line separator <code class="code">s</code> has been found</li>
</ul>
<br>
</div>
<pre><span class="keyword">class type</span> <a name="TYPEenhanced_raw_in_channel"></a><a href="Netchannels.enhanced_raw_in_channel.html">enhanced_raw_in_channel</a> = <code class="code">object</code> <a href="Netchannels.enhanced_raw_in_channel.html">..</a> <code class="code">end</code></pre><div class="info">
Defines private methods reading text line by line
</div>
<pre><span class="keyword">class</span> <a name="TYPEbuffered_raw_in_channel"></a><a href="Netchannels.buffered_raw_in_channel.html">buffered_raw_in_channel</a> : <code class="type">?eol:string list -> ?buffer_size:int -> <a href="Netchannels.raw_in_channel.html">raw_in_channel</a> -> </code><code class="type"><a href="Netchannels.enhanced_raw_in_channel.html">enhanced_raw_in_channel</a></code></pre><div class="info">
This class adds a buffer to the underlying <code class="code">raw_in_channel</code>.
</div>
<pre><span class="keyword">class</span> <a name="TYPEbuffered_raw_out_channel"></a><a href="Netchannels.buffered_raw_out_channel.html">buffered_raw_out_channel</a> : <code class="type">?buffer_size:int -> <a href="Netchannels.raw_out_channel.html">raw_out_channel</a> -> </code><code class="type"><a href="Netchannels.raw_out_channel.html">raw_out_channel</a></code></pre><div class="info">
This class adds a buffer to the underlying <code class="code">raw_out_channel</code>.
</div>
<br>
<a name="descriptors"></a>
<h1>Channels over descriptors</h1><br>
<pre><span class="keyword">class</span> <a name="TYPEinput_descr"></a><a href="Netchannels.input_descr.html">input_descr</a> : <code class="type">?blocking:bool -> ?start_pos_in:int -> Unix.file_descr -> </code><code class="type"><a href="Netchannels.raw_in_channel.html">raw_in_channel</a></code></pre><div class="info">
Creates a <code class="code">raw_in_channel</code> for the passed file descriptor, which must
be open for reading.
</div>
<pre><span class="keyword">class</span> <a name="TYPEoutput_descr"></a><a href="Netchannels.output_descr.html">output_descr</a> : <code class="type">?blocking:bool -> ?start_pos_out:int -> Unix.file_descr -> </code><code class="type"><a href="Netchannels.raw_out_channel.html">raw_out_channel</a></code></pre><div class="info">
Creates a <code class="code">raw_out_channel</code> for the passed file descriptor, which must
be open for writing.
</div>
<pre><span class="keyword">class</span> <a name="TYPEsocket_descr"></a><a href="Netchannels.socket_descr.html">socket_descr</a> : <code class="type">?blocking:bool -> ?start_pos_in:int -> ?start_pos_out:int -> Unix.file_descr -> </code><code class="type"><a href="Netchannels.raw_io_channel.html">raw_io_channel</a></code></pre><div class="info">
Creates a <code class="code">raw_io_channel</code> for the passed socket descriptor, which must
be open for reading and writing, and not yet shut down in either
direction.
</div>
<br>
<a name="transactional"></a>
<h1>Transactional channels</h1><br>
<pre><span class="keyword">type</span> <a name="TYPEclose_mode"></a><code class="type"></code>close_mode = <code class="type">[ `Commit | `Rollback ]</code> </pre>
<div class="info">
Whether a <code class="code">close_out</code> implies a commit or rollback operation<br>
</div>
<pre><span class="keyword">class</span> <a name="TYPEbuffered_trans_channel"></a><a href="Netchannels.buffered_trans_channel.html">buffered_trans_channel</a> : <code class="type">?close_mode:<a href="Netchannels.html#TYPEclose_mode">close_mode</a> -> <a href="Netchannels.out_obj_channel.html">out_obj_channel</a> -> </code><code class="type"><a href="Netchannels.trans_out_obj_channel.html">trans_out_obj_channel</a></code></pre><div class="info">
A transactional output channel with a transaction buffer implemented
in memory
</div>
<pre><span class="keyword">val</span> <a name="VALmake_temporary_file"></a>make_temporary_file : <code class="type">?mode:int -><br> ?limit:int -><br> ?tmp_directory:string -><br> ?tmp_prefix:string -><br> unit -> string * Pervasives.in_channel * Pervasives.out_channel</code></pre><div class="info">
Creates a temporary file in the directory <code class="code">tmp_directory</code> with a name
prefix <code class="code">tmp_prefix</code> and a unique suffix. The function returns
the triple (name, inch, outch) containing the file <code class="code">name</code>,
the file opened as in_channel <code class="code">inch</code> and as out_channel <code class="code">outch</code>.
<p>
<br>
</div>
<div class="param_info"><code class="code">mode</code> : The creation mask of the file; defaults to 0o600, i.e. the
file is private for the current user</div>
<div class="param_info"><code class="code">limit</code> : Limits the number of trials to find the unique suffix.
Defaults to 1000.</div>
<div class="param_info"><code class="code">tmp_directory</code> : By default the current directory</div>
<div class="param_info"><code class="code">tmp_prefix</code> : By default <code class="code">"netstring"</code>. It is better to have a prefix
that is likely to be unique, e.g. the process ID, or the current time.</div>
<pre><span class="keyword">class</span> <a name="TYPEtempfile_trans_channel"></a><a href="Netchannels.tempfile_trans_channel.html">tempfile_trans_channel</a> : <code class="type">?close_mode:<a href="Netchannels.html#TYPEclose_mode">close_mode</a> -> ?tmp_directory:string -> ?tmp_prefix:string -> <a href="Netchannels.out_obj_channel.html">out_obj_channel</a> -> </code><code class="type"><a href="Netchannels.trans_out_obj_channel.html">trans_out_obj_channel</a></code></pre><div class="info">
A transactional output channel with a transaction buffer implemented
as temporary file
</div>
<br>
<a name="filters"></a>
<h1>Pipes and Filters</h1><br>
<br>
Note that this has nothing to do with "pipes" on the Unix level.
It is, however, the same idea: Connecting two I/O resources with an
intermediate buffer.<br>
<pre><span class="keyword">class</span> <a name="TYPEpipe"></a><a href="Netchannels.pipe.html">pipe</a> : <code class="type">?conv:<a href="Netbuffer.html#TYPEt">Netbuffer.t</a> -> bool -> <a href="Netbuffer.html#TYPEt">Netbuffer.t</a> -> unit -> unit -> </code><code class="type"><a href="Netchannels.io_obj_channel.html">io_obj_channel</a></code></pre><div class="info">
A <code class="code">pipe</code> has two internal buffers (realized by Netbuffer).
</div>
<pre><span class="keyword">class</span> <a name="TYPEoutput_filter"></a><a href="Netchannels.output_filter.html">output_filter</a> : <code class="type"><a href="Netchannels.io_obj_channel.html">io_obj_channel</a> -> <a href="Netchannels.out_obj_channel.html">out_obj_channel</a> -> </code><code class="type"><a href="Netchannels.out_obj_channel.html">out_obj_channel</a></code></pre><div class="info">
An <code class="code">output_filter</code> filters the data written to it through the
<code class="code">io_obj_channel</code> (usually a <code class="code">pipe</code>), and writes the filtered data
to the passed <code class="code">out_obj_channel</code>.
</div>
<pre><span class="keyword">class</span> <a name="TYPEinput_filter"></a><a href="Netchannels.input_filter.html">input_filter</a> : <code class="type"><a href="Netchannels.in_obj_channel.html">in_obj_channel</a> -> <a href="Netchannels.io_obj_channel.html">io_obj_channel</a> -> </code><code class="type"><a href="Netchannels.in_obj_channel.html">in_obj_channel</a></code></pre><div class="info">
An <code class="code">input_filter</code> filters the data read from it through the
<code class="code">io_obj_channel</code> (usually a <code class="code">pipe</code> after the data have been
retrieved from the passed <code class="code">in_obj_channel</code>.
</div>
<br>
<a name="filters_notes"></a>
<h2>Notes, Examples</h2><br>
<br>
If you have the choice, prefer <code class="code">output_filter</code> over <code class="code">input_filter</code>.
The latter is slower.
<p>
The primary application of filters is to encode or decode a channel
on the fly. For example, the following lines write a BASE64-encoded file:
<p>
<pre><code class="code">let ch = new output_channel (open_out "file.b64") in
let encoder = new Netencoding.Base64.encoding_pipe ~linelength:76 () in
let ch' = new output_filter encoder ch in
... (* write to ch' *)
ch' # close_out();
ch # close_out(); (* you must close both channels! *)
</code></pre>
<p>
All bytes written to <code class="code">ch'</code> are BASE64-encoded and the encoded bytes are
written to <code class="code">ch</code>.
<p>
There are also pipes to decode BASE64, and to encode and decode the
"Quoted printable" format. Encoding and decoding work even if the
data is delivered in disadvantageous chunks, because the data is
"re-chunked" if needed. For example, BASE64 would require that data
arrive in multiples of three bytes, and to cope with that, the BASE64 pipe
only processes the prefix of the input buffer that is a multiple of three,
and defers the encoding of the extra bytes till the next opportunity.<br>
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