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/* Copyright (C) 1993, 1995, 1997, 1999 Aladdin Enterprises. All rights reserved.
This software is licensed to a single customer by Artifex Software Inc.
under the terms of a specific OEM agreement.
*/
/*$RCSfile$ $Revision$ */
/* Definitions for stream implementors */
/* Requires stdio.h */
#ifndef strimpl_INCLUDED
# define strimpl_INCLUDED
#include "scommon.h"
#include "gstypes.h" /* for gsstruct.h */
#include "gsstruct.h"
/*
* The 'process' procedure does the real work of the stream.
* It must process as much input information (from pr->ptr + 1 through
* pr->limit) as it can, subject to space available for output
* (pw->ptr + 1 through pw->limit), updating pr->ptr and pw->ptr.
*
* The procedure return value must be one of:
* EOFC - an end-of-data pattern was detected in the input,
* or no more input can be processed for some other reason (e.g.,
* the stream was told only to read a certain amount of data).
* ERRC - a syntactic error was detected in the input.
* 0 - more input data is needed.
* 1 - more output space is needed.
* If the procedure returns EOFC, it can assume it will never be called
* again for that stream.
*
* If the procedure is called with last = 1, this is an indication that
* no more input will ever be supplied (after the input in the current
* buffer defined by *pr); the procedure should produce as much output
* as possible, including an end-of-data marker if applicable. In this
* case:
* - If the procedure returns 1, it may be called again (also with
* last = 1).
* - If the procedure returns any other value other than 1, the
* procedure will never be called again for that stream.
* - If the procedure returns 0, this is taken as equivalent to
* returning EOFC.
* - If the procedure returns EOFC (or 0), the stream's end_status
* is set to EOFC, meaning no more writing is allowed.
*
* Note that these specifications do not distinguish input from output
* streams. This is deliberate: The processing procedures should work
* regardless of which way they are oriented in a stream pipeline.
* (The PostScript language does take a position as whether any given
* filter may be used for input or output, but this occurs at a higher level.)
*
* The value returned by the process procedure of a stream whose data source
* or sink is external (i.e., not another stream) is interpreted slightly
* differently. For an external data source, a return value of 0 means
* "no more input data are available now, but more might become available
* later." For an external data sink, a return value of 1 means "there is
* no more room for output data now, but there might be room later."
*
* It appears that the Adobe specifications, read correctly, require that when
* the process procedure of a decoding filter has filled up the output
* buffer, it must still peek ahead in the input to determine whether or not
* the next thing in the input stream is EOD. If the next thing is an EOD (or
* end-of-data, indicated by running out of input data with last = true), the
* process procedure must return EOFC; if the next thing is definitely not
* an EOD, the process procedure must return 1 (output full) (without, of
* course, consuming the non-EOD datum); if the procedure cannot determine
* whether or not the next thing is an EOD, it must return 0 (need more input).
* Decoding filters that don't have EOD (for example, NullDecode) can use
* a simpler algorithm: if the output buffer is full, then if there is more
* input, return 1, otherwise return 0 (which is taken as EOFC if last
* is true). All this may seem a little awkward, but it is needed in order
* to have consistent behavior regardless of where buffer boundaries fall --
* in particular, if a buffer boundary falls just before an EOD. It is
* actually quite easy to implement if the main loop of the process
* procedure tests for running out of input rather than for filling the
* output: with this structure, exhausting the input always returns 0,
* and discovering that the output buffer is full when attempting to store
* more output always returns 1.
*
* Even this algorithm for handling end-of-buffer is not sufficient if an
* EOD falls just after a buffer boundary, but the generic stream code
* handles this case: the process procedures need only do what was just
* described.
*/
/*
* The set_defaults procedure in the template has a dual purpose: it sets
* default values for all parameters that the client can set before calling
* the init procedure, and it also must initialize all pointers in the
* stream state to a value that will be valid for the garbage collector
* (normally 0). The latter implies that:
*
* Any stream whose state includes additional pointers (beyond those
* in stream_state_common) must have a set_defaults procedure.
*/
/*
* Define a template for creating a stream.
*
* The meaning of min_in_size and min_out_size is the following:
* If the amount of input information is at least min_in_size,
* and the available output space is at least min_out_size,
* the process procedure guarantees that it will make some progress.
* (It may make progress even if this condition is not met, but this is
* not guaranteed.)
*/
struct stream_template_s {
/* Define the structure type for the stream state. */
gs_memory_type_ptr_t stype;
/* Define an optional initialization procedure. */
stream_proc_init((*init));
/* Define the processing procedure. */
/* (The init procedure can reset other procs if it wants.) */
stream_proc_process((*process));
/* Define the minimum buffer sizes. */
uint min_in_size; /* minimum size for process input */
uint min_out_size; /* minimum size for process output */
/* Define an optional releasing procedure. */
stream_proc_release((*release));
/* Define an optional parameter defaulting and pointer initialization */
/* procedure. */
stream_proc_set_defaults((*set_defaults));
/* Define an optional reinitialization procedure. */
stream_proc_reinit((*reinit));
};
/* Utility procedures */
int stream_move(P2(stream_cursor_read *, stream_cursor_write *)); /* in stream.c */
/* Hex decoding utility procedure */
typedef enum {
hex_ignore_garbage = 0,
hex_ignore_whitespace = 1,
hex_ignore_leading_whitespace = 2
} hex_syntax;
int s_hex_process(P4(stream_cursor_read *, stream_cursor_write *, int *, hex_syntax)); /* in sstring.c */
#endif /* strimpl_INCLUDED */
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