W3C Sample Code Library libwww I/O Stream Classes

# I/O Stream Classes

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

The I/O Stream class defines objects which accepts a sequence of characters to and from a transport The input and output stream are mainly derived from the generic stream class and contains much of the same functionality. The main difference is that the I/O streams also contains methods for reading and writing to a transport.

This module is a part of the W3C Sample Code Library.

    #ifndef HTIOSTREAM_H
    #define HTIOSTREAM_H

    typedef struct _HTInputStream HTInputStream;
    typedef struct _HTOutputStream HTOutputStream;

    #include "HTList.h"
    #include "HTStream.h"
    #include "HTChannl.h"

## Input Stream

An input stream is a stream that can read data from a transport and via a channel putting the data down to the application.

    typedef struct _HTInputStreamClass {

        char * name;

This field is for diagnostics only

        int (*flush)	(HTInputStream * me);

The flush method is introduced in order to allow the stream to put any buffered data down the stream pipe but without taking the stream pipe down. It is for the stream to decide whether it has buffered data or not. In some situations, the stream might not want to send buffered data down the target as the date might be relevant for this stream only.

        int (*_free)	(HTInputStream * me);

The `free` method is like the `flush` method but it also frees the current stream object and all stream objects down stream. When the `free` method has been called, the whole stream pipe (not only this object) should not accept any more data. See also the `close` method below

        int (*abort)	(HTInputStream * me, HTList * errorlist);

The abort method should only be used if a stream is interrupted, for example by the user, or an error occurs.

        int (*read)		(HTInputStream * me);

The read method is the method by which we can read data from the transport layer.

        int (*close)	(HTInputStream * me);

Pipelined transports need to know how many bytes were consumed by the net object.

        int (*consumed)	(HTInputStream * me, size_t bytes);

The `close` method closes the transport and deletes the input stream object. Note that this is different than the free method which doesn't have to delete the input stream object itself.

    } HTInputStreamClass;

## Output Stream

The output stream is similar to the generic stream definition in that it has a superset of methods. The `param` parameter and the `mode` parameter can be used for whatever purpose suited.

    typedef struct _HTOutputStreamClass {

        char * name;

        int (*flush)	(HTOutputStream * me);

        int (*_free)	(HTOutputStream * me);

        int (*abort)	(HTOutputStream * me, HTList * errorlist);

        int (*put_character)(HTOutputStream * me, char ch);

        int (*put_string)	(HTOutputStream * me, const char * str);

        int (*put_block)	(HTOutputStream * me, const char * str, int len);

See the generic Stream Definition for an explanation of these methods. Note that they all have a `HTOutputStream` object a the parameter, not a generic stream. This is to avoid incompatible pointer warnings

        int (*close)	(HTOutputStream * me);

The `close` method closes the transport and deletes the input stream object. Note that this is different than the free method which doesn't have to delete the input stream object itself.

    } HTOutputStreamClass;

## Transport Streams

Transport streams are special streams with creation methods like defined below. Transport streams can be registered in a transport object as ways of communicating with the a transport.

### Transport Input Stream

We have two modes of the input stream depending on model used for data reading is PUSH or PULL. The PUSH model is suitable if we are using pseudo threads based on a `select()` call or equivalent and the PULL is suitable in a real thread environment. In the latter case it doesn't matter if a read procedure blocks as this only concerns a single thread.

    typedef HTInputStream * HTInput_new	(HTHost *	host,
    					 HTChannel *	ch,
    					 void *		param,
    					 int		mode);

### Transport Output Stream

    typedef HTOutputStream * HTOutput_new	(HTHost *	host,
    					 HTChannel *	ch,
    					 void *		param,
    					 int		mode);

### Transport Output Stream Converter

    typedef HTOutputStream * HTOutputConverter_new(
    	HTHost *		host,
    	HTChannel *		ch,
    	void *			param,
    	int			mode,
    	HTOutputStream *	target);

    #endif /* HTIOSTREAM_H */