# The Channel Class

    /*
    **	(c) COPYRIGHT MIT 1995.
    **	Please first read the full copyright statement in the file COPYRIGH.
    */

A channel contains information about sockets and their input and output streams. A `channel` 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:

- Reading data on a channel
- Defining a target for incoming data
- Defining a protocol state machine that can handle the data

This module is implemented by HTChannl.c, and it is a part of the W3C Sample Code Library.

    #ifndef HTCHANNL_H
    #define HTCHANNL_H

    typedef struct _HTChannel HTChannel;

    #include "HTHost.h"
    #include "HTIOStream.h"

## The Channel Object

The channel object contains an input and an output stream for a particular connection.

### Creation and Deletion of Channel Objects

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

    extern HTChannel * HTChannel_new (SOCKET sockfd, FILE * fp, BOOL active);

### Deleting a Channel Object

    extern BOOL HTChannel_delete (HTChannel * channel, int status);
    extern BOOL HTChannel_deleteAll (void);

### Search for a Channel

Look for a channel object if we for some reason should have lost it

    extern HTChannel * HTChannel_find (SOCKET sockfd);

### Get Transport Descriptor for Channel

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.

    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);

### The Host Object

The Channel object also keeps a link to the host object so that we have a link to the persistent connection repository.

    extern BOOL HTChannel_setHost (HTChannel * ch, HTHost * host);
    extern HTHost * HTChannel_host (HTChannel * ch);

### Semaphores

Adjust the semaphore on a channel. As many Net objects 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

    extern void HTChannel_upSemaphore   (HTChannel * channel);
    extern void HTChannel_downSemaphore (HTChannel * channel);
    extern void HTChannel_setSemaphore  (HTChannel * channel, int semaphore);

### Create Input and Output Streams

You create the input stream and bind it to the channel using the following methods. Please read the description in the HTIOStream module on the parameters target, param, and mode. The input and output stream are instances created by the Transport object. The Transport Object defines the creation methods for the inout and output streams and the Channel object contains the actualy stream objects.

    extern BOOL HTChannel_setInput (HTChannel * ch, HTInputStream * input);
    extern HTInputStream * HTChannel_input (HTChannel * ch);

    extern BOOL HTChannel_setOutput (HTChannel * ch, HTOutputStream * output);
    extern HTOutputStream * HTChannel_output (HTChannel * ch);

    extern HTInputStream * HTChannel_getChannelIStream (HTChannel * ch);
    extern HTOutputStream * HTChannel_getChannelOStream (HTChannel * ch);

    #endif /* HTCHANNL */