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<HTML>
<HEAD>
  <TITLE>W3C Sample Code Library libwww Channel Interface</TITLE>
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<H1>
  The Channel Class
</H1>
<PRE>
/*
**	(c) COPYRIGHT MIT 1995.
**	Please first read the full copyright statement in the file COPYRIGH.
*/
</PRE>
<P>
A channel contains information about sockets and their input and output streams.
A <CODE>channel</CODE> represents the front end for receiving data towards
the underlying transport. The definition of a channel describes how we are
to read the data coming in on a socket, for example. In other words - a channel
represents the first part of how to get handle incoming data in the Library:
<P>
<UL>
  <LI>
    Reading data on a channel
  <LI>
    Defining a target for incoming data
  <LI>
    Defining a protocol state machine that can handle the data
</UL>
<P>
This module is implemented by <A HREF="HTChannl.c">HTChannl.c</A>, and it
is a part of the <A HREF="http://www.w3.org/Library/"> W3C Sample Code
Library</A>.
<PRE>
#ifndef HTCHANNL_H
#define HTCHANNL_H

#ifdef __cplusplus
extern "C" { 
#endif 

typedef struct _HTChannel HTChannel;

#include <A HREF="HTHost.html">"HTHost.h"</A>
#include <A HREF="HTIOStream.html">"HTIOStream.h"</A>
</PRE>
<H2>
  The Channel Object
</H2>
<P>
The channel object contains an input and an output stream for a particular
connection.
<H3>
  Creation and Deletion of Channel Objects
</H3>

Either the socket can be invalid (INVSOC) or the file descriptor can
be NULL but not both.

<PRE>
extern HTChannel * HTChannel_new (SOCKET sockfd, FILE * fp, BOOL active);
</PRE>
<H3>
  Deleting a Channel Object
</H3>
<PRE>
extern BOOL HTChannel_delete (HTChannel * channel, int status);
extern BOOL HTChannel_deleteAll (void);
extern BOOL HTChannel_safeDeleteAll (void);
</PRE>
<H3>
  Search for a Channel
</H3>
<P>
Look for a channel object if we for some reason should have lost it
<PRE>
extern HTChannel * HTChannel_find (SOCKET sockfd);
</PRE>
<H3>
  Get Transport Descriptor for Channel
</H3>
<P>
A transport descriptor can be either a ANSI C file descriptor or a BSD socket.
As it is difficult for the channel to know which one is used by a specific
transport, we leave this to the caller to figure out. This is probably not
the best way of doing it.
<PRE>
extern SOCKET HTChannel_socket	(HTChannel * channel);
extern BOOL HTChannel_setSocket	(HTChannel * channel, SOCKET socket);

extern FILE * HTChannel_file	(HTChannel * channel);
extern BOOL HTChannel_setFile   (HTChannel * channel, FILE * fp);
</PRE>
<H3>
  The Host Object
</H3>
<P>
The Channel object also keeps a link to the <A HREF="HTHost.html">host
object</A> so that we have a link to the persistent connection repository.
<PRE>extern BOOL HTChannel_setHost (HTChannel * ch, HTHost * host);
extern HTHost * HTChannel_host (HTChannel * ch);
</PRE>
<H3>
  Semaphores
</H3>
<P>
Adjust the semaphore on a channel. As many <A HREF="HTNet.html">Net objects
</A>can point to the same channel we need to keep count of them so that we
know if we can delete a channel or if it is still in use. We do this by having
a simple semaphore associated with each channel object
<PRE>
extern void HTChannel_upSemaphore   (HTChannel * channel);
extern void HTChannel_downSemaphore (HTChannel * channel);
extern void HTChannel_setSemaphore  (HTChannel * channel, int semaphore);
</PRE>
<H3>
  Create Input and Output Streams
</H3>
<P>
You create the input stream and bind it to the channel using the following
methods. Please read the description in the
<A HREF="HTIOStream.html">HTIOStream module</A> on the parameters
<EM>target</EM>, <EM>param</EM>, and <EM>mode</EM>. The input and output
stream are instances created by the <A HREF="HTTrans.html">Transport
object</A>. The Transport Object defines the creation methods for the inout
and output streams and the Channel object contains the actualy stream objects.
<PRE>
extern BOOL HTChannel_setInput (HTChannel * ch, HTInputStream * input);
extern HTInputStream * HTChannel_input (HTChannel * ch);
extern BOOL HTChannel_deleteInput (HTChannel * channel, int status);

extern BOOL HTChannel_setOutput (HTChannel * ch, HTOutputStream * output);
extern HTOutputStream * HTChannel_output (HTChannel * ch);
extern BOOL HTChannel_deleteOutput (HTChannel * channel, int status);

extern HTInputStream * HTChannel_getChannelIStream (HTChannel * ch);
extern HTOutputStream * HTChannel_getChannelOStream (HTChannel * ch);
</PRE>
<PRE>
#ifdef __cplusplus
}
#endif

#endif /* HTCHANNL */
</PRE>
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