src/png/pngrio.c

   1
   2 /* pngrio.c - functions for data input
   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 input.  Users who need
  14  * special handling are expected to write a function that has the same
  15  * arguments as this and performs a similar function, but that possibly
  16  * has a different input method.  Note that you shouldn't change this
  17  * function, but rather write a replacement function and then make
  18  * libpng use it at run time with png_set_read_fn(...).
  19  */
  20
  21 #include "pngpriv.h"
  22
  23 #ifdef PNG_READ_SUPPORTED
  24
  25 /* Read the data from whatever input you are using.  The default routine
  26  * reads from 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 reads.  This should never be asked
  29  * to read more then 64K on a 16 bit machine.
  30  */
  31 void /* PRIVATE */
  32 png_read_data(png_structrp png_ptr, png_bytep data, png_size_t length)
  33 {
  34    png_debug1(4, "reading %d bytes", (int)length);
  35
  36    if (png_ptr->read_data_fn != NULL)
  37       (*(png_ptr->read_data_fn))(png_ptr, data, length);
  38
  39    else
  40       png_error(png_ptr, "Call to NULL read function");
  41 }
  42
  43 #ifdef PNG_STDIO_SUPPORTED
  44 /* This is the function that does the actual reading of data.  If you are
  45  * not reading from a standard C stream, you should create a replacement
  46  * read_data function and use it at run time with png_set_read_fn(), rather
  47  * than changing the library.
  48  */
  49 void PNGCBAPI
  50 png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
  51 {
  52    png_size_t check;
  53
  54    if (png_ptr == NULL)
  55       return;
  56
  57    /* fread() returns 0 on error, so it is OK to store this in a png_size_t
  58     * instead of an int, which is what fread() actually returns.
  59     */
  60    check = fread(data, 1, length, png_voidcast(png_FILE_p, png_ptr->io_ptr));
  61
  62    if (check != length)
  63       png_error(png_ptr, "Read Error");
  64 }
  65 #endif
  66
  67 /* This function allows the application to supply a new input function
  68  * for libpng if standard C streams aren't being used.
  69  *
  70  * This function takes as its arguments:
  71  *
  72  * png_ptr      - pointer to a png input data structure
  73  *
  74  * io_ptr       - pointer to user supplied structure containing info about
  75  *                the input functions.  May be NULL.
  76  *
  77  * read_data_fn - pointer to a new input function that takes as its
  78  *                arguments a pointer to a png_struct, a pointer to
  79  *                a location where input data can be stored, and a 32-bit
  80  *                unsigned int that is the number of bytes to be read.
  81  *                To exit and output any fatal error messages the new write
  82  *                function should call png_error(png_ptr, "Error msg").
  83  *                May be NULL, in which case libpng's default function will
  84  *                be used.
  85  */
  86 void PNGAPI
  87 png_set_read_fn(png_structrp png_ptr, png_voidp io_ptr,
  88    png_rw_ptr read_data_fn)
  89 {
  90    if (png_ptr == NULL)
  91       return;
  92
  93    png_ptr->io_ptr = io_ptr;
  94
  95 #ifdef PNG_STDIO_SUPPORTED
  96    if (read_data_fn != NULL)
  97       png_ptr->read_data_fn = read_data_fn;
  98
  99    else
 100       png_ptr->read_data_fn = png_default_read_data;
 101 #else
 102    png_ptr->read_data_fn = read_data_fn;
 103 #endif
 104
 105    /* It is an error to write to a read device */
 106    if (png_ptr->write_data_fn != NULL)
 107    {
 108       png_ptr->write_data_fn = NULL;
 109       png_warning(png_ptr,
 110           "Can't set both read_data_fn and write_data_fn in the"
 111           " same structure");
 112    }
 113
 114 #ifdef PNG_WRITE_FLUSH_SUPPORTED
 115    png_ptr->output_flush_fn = NULL;
 116 #endif
 117 }
 118 #endif /* PNG_READ_SUPPORTED */