src/png/pngwio.c

   1
   2 /* pngwio.c - functions for data output
   3  *
   4  * Last changed in libpng 1.6.0 [February 14, 2013]
   5  * Copyright (c) 1998-2013 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
  32 void /* PRIVATE */
  33 png_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  */
  50 void PNGCBAPI
  51 png_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
  70 void /* PRIVATE */
  71 png_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
  78 void PNGCBAPI
  79 png_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  */
 121 void PNGAPI
 122 png_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 #endif /* PNG_WRITE_FLUSH_SUPPORTED */
 153
 154    /* It is an error to read while writing a png file */
 155    if (png_ptr->read_data_fn != NULL)
 156    {
 157       png_ptr->read_data_fn = NULL;
 158
 159       png_warning(png_ptr,
 160           "Can't set both read_data_fn and write_data_fn in the"
 161           " same structure");
 162    }
 163 }
 164 #endif /* PNG_WRITE_SUPPORTED */