1
  2/* pngwio.c - functions for data output
  3 *
  4 * Last changed in libpng 1.6.24 [August 4, 2016]
  5 * Copyright (c) 1998-2002,2004,2006-2014,2016 Glenn Randers-Pehrson
  6 * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
  7 * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
  8 *
  9 * This code is released under the libpng license.
 10 * For conditions of distribution and use, see the disclaimer
 11 * and license in png.h
 12 *
 13 * This file provides a location for all output.  Users who need
 14 * special handling are expected to write functions that have the same
 15 * arguments as these and perform similar functions, but that possibly
 16 * use different output methods.  Note that you shouldn't change these
 17 * functions, but rather write replacement functions and then change
 18 * them at run time with png_set_write_fn(...).
 19 */
 20
 21#include "pngpriv.h"
 22
 23#ifdef PNG_WRITE_SUPPORTED
 24
 25/* Write the data to whatever output you are using.  The default routine
 26 * writes to a file pointer.  Note that this routine sometimes gets called
 27 * with very small lengths, so you should implement some kind of simple
 28 * buffering if you are using unbuffered writes.  This should never be asked
 29 * to write more than 64K on a 16-bit machine.
 30 */
 31
 32void /* PRIVATE */
 33png_write_data(png_structrp png_ptr, png_const_bytep data, png_size_t length)
 34{
 35   /* NOTE: write_data_fn must not change the buffer! */
 36   if (png_ptr->write_data_fn != NULL )
 37      (*(png_ptr->write_data_fn))(png_ptr, png_constcast(png_bytep,data),
 38          length);
 39
 40   else
 41      png_error(png_ptr, "Call to NULL write function");
 42}
 43
 44#ifdef PNG_STDIO_SUPPORTED
 45/* This is the function that does the actual writing of data.  If you are
 46 * not writing to a standard C stream, you should create a replacement
 47 * write_data function and use it at run time with png_set_write_fn(), rather
 48 * than changing the library.
 49 */
 50void PNGCBAPI
 51png_default_write_data(png_structp png_ptr, png_bytep data, png_size_t length)
 52{
 53   png_size_t check;
 54
 55   if (png_ptr == NULL)
 56      return;
 57
 58   check = fwrite(data, 1, length, (png_FILE_p)(png_ptr->io_ptr));
 59
 60   if (check != length)
 61      png_error(png_ptr, "Write Error");
 62}
 63#endif
 64
 65/* This function is called to output any data pending writing (normally
 66 * to disk).  After png_flush is called, there should be no data pending
 67 * writing in any buffers.
 68 */
 69#ifdef PNG_WRITE_FLUSH_SUPPORTED
 70void /* PRIVATE */
 71png_flush(png_structrp png_ptr)
 72{
 73   if (png_ptr->output_flush_fn != NULL)
 74      (*(png_ptr->output_flush_fn))(png_ptr);
 75}
 76
 77#  ifdef PNG_STDIO_SUPPORTED
 78void PNGCBAPI
 79png_default_flush(png_structp png_ptr)
 80{
 81   png_FILE_p io_ptr;
 82
 83   if (png_ptr == NULL)
 84      return;
 85
 86   io_ptr = png_voidcast(png_FILE_p, (png_ptr->io_ptr));
 87   fflush(io_ptr);
 88}
 89#  endif
 90#endif
 91
 92/* This function allows the application to supply new output functions for
 93 * libpng if standard C streams aren't being used.
 94 *
 95 * This function takes as its arguments:
 96 * png_ptr       - pointer to a png output data structure
 97 * io_ptr        - pointer to user supplied structure containing info about
 98 *                 the output functions.  May be NULL.
 99 * write_data_fn - pointer to a new output function that takes as its
100 *                 arguments a pointer to a png_struct, a pointer to
101 *                 data to be written, and a 32-bit unsigned int that is
102 *                 the number of bytes to be written.  The new write
103 *                 function should call png_error(png_ptr, "Error msg")
104 *                 to exit and output any fatal error messages.  May be
105 *                 NULL, in which case libpng's default function will
106 *                 be used.
107 * flush_data_fn - pointer to a new flush function that takes as its
108 *                 arguments a pointer to a png_struct.  After a call to
109 *                 the flush function, there should be no data in any buffers
110 *                 or pending transmission.  If the output method doesn't do
111 *                 any buffering of output, a function prototype must still be
112 *                 supplied although it doesn't have to do anything.  If
113 *                 PNG_WRITE_FLUSH_SUPPORTED is not defined at libpng compile
114 *                 time, output_flush_fn will be ignored, although it must be
115 *                 supplied for compatibility.  May be NULL, in which case
116 *                 libpng's default function will be used, if
117 *                 PNG_WRITE_FLUSH_SUPPORTED is defined.  This is not
118 *                 a good idea if io_ptr does not point to a standard
119 *                 *FILE structure.
120 */
121void PNGAPI
122png_set_write_fn(png_structrp png_ptr, png_voidp io_ptr,
123    png_rw_ptr write_data_fn, png_flush_ptr output_flush_fn)
124{
125   if (png_ptr == NULL)
126      return;
127
128   png_ptr->io_ptr = io_ptr;
129
130#ifdef PNG_STDIO_SUPPORTED
131   if (write_data_fn != NULL)
132      png_ptr->write_data_fn = write_data_fn;
133
134   else
135      png_ptr->write_data_fn = png_default_write_data;
136#else
137   png_ptr->write_data_fn = write_data_fn;
138#endif
139
140#ifdef PNG_WRITE_FLUSH_SUPPORTED
141#  ifdef PNG_STDIO_SUPPORTED
142
143   if (output_flush_fn != NULL)
144      png_ptr->output_flush_fn = output_flush_fn;
145
146   else
147      png_ptr->output_flush_fn = png_default_flush;
148
149#  else
150   png_ptr->output_flush_fn = output_flush_fn;
151#  endif
152#else
153   PNG_UNUSED(output_flush_fn)
154#endif /* WRITE_FLUSH */
155
156#ifdef PNG_READ_SUPPORTED
157   /* It is an error to read while writing a png file */
158   if (png_ptr->read_data_fn != NULL)
159   {
160      png_ptr->read_data_fn = NULL;
161
162      png_warning(png_ptr,
163          "Can't set both read_data_fn and write_data_fn in the"
164          " same structure");
165   }
166#endif
167}
168#endif /* WRITE */