/*                                          W3C Reference Library libwww Generic Stream Class
                                   GENERIC STREAM CLASS
                                             
 */
/*
**      (c) COPYRIGHT MIT 1995.
**      Please first read the full copyright statement in the file COPYRIGH.
*/
/*

   The Stream class defines objects which accepts a sequence of characters. Streams may
   also have an output in which case multiple stream objects can be cascaded to build a
   stream pipe where the output of a stream is directed into the input of the next stream
   object "down the line". Of course, one of the main features of streams is that they can
   perform a _data conversion_on the data before piping it to the output. As multiple
   streams may be cascaded, the complete data conversion is then the sum of each
   individual data conversion performed by the stream objects being part of the stream
   pipe.
   
   It is not _required_ that a stream has a target, it might as well be a black hole that
   just accepts data without ever giving it out again. The generic stream class is
   subclassed multiple places in the Library and a good example is the structured stream
   definition which creates a SGML object.
   
   All stream class methods return an integer status code telling whether the operation
   succeeded or not.. This is the way for a stream to pass control information upstream to
   the caller which may also be a stream. The general return codes from the methods are:
   
      _HT_WOULD_BLOCK_
      
      _HT_ERROR_
      
      _HT_OK_
      
      _>0_ - any return greater than 0 will result in that the return code will be parsed
      through all stream objects. This can be used to pass back information to the
      protocol modules, for example
      
   It is in general not relevant to return how much data has been written in the stream,
   as there often will be a relationship other than 1:1 between indata and outdata.
   However, it is important that a stream keeps state (either on the incoming data or the
   outgoing data stream) so that it can accept a HT_WOULD_BLOCKand continue at a later
   time when the blocking situation has stopped.
   
   This module is implemented by HTStream.c, and it is a part of the W3C Reference
   Library.
   
 */
#ifndef HTSTREAM_H
#define HTSTREAM_H

#include "HTList.h"

typedef struct _HTStream HTStream;

typedef struct _HTStreamClass {

    char * name;
/*

   This field is for diagnostics only
   
 */
    int (*flush)        (HTStream * 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)        (HTStream * me);
/*

   The _free_ method is like the flushmethod but it also frees the current stream object
   and all stream objects down stream. When the freemethod has been called, the
   wholestream pipe (not only this obejct) should not accept any more data.
   
 */
    int (*abort)        (HTStream * 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 (*put_character)(HTStream * me, char ch);
                                
    int (*put_string)   (HTStream * me, const char * str);

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

   These methods are for actually putting data down the stream. It is important that the
   most efficient method is chosen (often put_block). There is no guarantee that a stream
   won't change method, for example from put_characterto put_block
   
 */
} HTStreamClass;
/*

BASIC UTILITY STREAMS

   These streams can be plugged in everywhere in a stream pipe.
   
  Black Hole Stream
  
   This stream simply absorbs data without doing anything what so ever.
   
 */
extern HTStream * HTBlackHole (void);
/*

  Generic Error Stream
  
   The Error stream simply returns HT_ERRORon all methods. This can be used to stop a
   stream as soon as data arrives, for example from the network.
   
 */
extern HTStream * HTErrorStream (void);
/*

 */
#endif /* HTSTREAM_H */
/*

   
   ___________________________________
   
                          @(#) $Id: HTStream.html,v 2.22 1996/05/20 15:07:14 frystyk Exp $
                                                                                          
    */
