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      1 
      2 /* pngrio.c - functions for data input
      3  *
      4  * Last changed in libpng 1.6.9 [February 6, 2014]
      5  * Copyright (c) 1998-2014 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 #ifdef PNG_INDEX_SUPPORTED
     42    png_ptr->total_data_read += length;
     43 #endif
     44 }
     45 
     46 #ifdef PNG_INDEX_SUPPORTED
     47 void /* PRIVATE */
     48 png_seek_data(png_structp png_ptr, png_uint_32 offset)
     49 {
     50    if (png_ptr->seek_data_fn != NULL)
     51       (*(png_ptr->seek_data_fn))(png_ptr, offset);
     52    else
     53       png_error(png_ptr, "Call to NULL seek function");
     54 }
     55 #endif
     56 
     57 #ifdef PNG_STDIO_SUPPORTED
     58 /* This is the function that does the actual reading of data.  If you are
     59  * not reading from a standard C stream, you should create a replacement
     60  * read_data function and use it at run time with png_set_read_fn(), rather
     61  * than changing the library.
     62  */
     63 void PNGCBAPI
     64 png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
     65 {
     66    png_size_t check;
     67 
     68    if (png_ptr == NULL)
     69       return;
     70 
     71    /* fread() returns 0 on error, so it is OK to store this in a png_size_t
     72     * instead of an int, which is what fread() actually returns.
     73     */
     74    check = fread(data, 1, length, png_voidcast(png_FILE_p, png_ptr->io_ptr));
     75 
     76    if (check != length)
     77       png_error(png_ptr, "Read Error");
     78 }
     79 #endif
     80 
     81 /* This function allows the application to supply a new input function
     82  * for libpng if standard C streams aren't being used.
     83  *
     84  * This function takes as its arguments:
     85  *
     86  * png_ptr      - pointer to a png input data structure
     87  *
     88  * io_ptr       - pointer to user supplied structure containing info about
     89  *                the input functions.  May be NULL.
     90  *
     91  * read_data_fn - pointer to a new input function that takes as its
     92  *                arguments a pointer to a png_struct, a pointer to
     93  *                a location where input data can be stored, and a 32-bit
     94  *                unsigned int that is the number of bytes to be read.
     95  *                To exit and output any fatal error messages the new write
     96  *                function should call png_error(png_ptr, "Error msg").
     97  *                May be NULL, in which case libpng's default function will
     98  *                be used.
     99  */
    100 void PNGAPI
    101 png_set_read_fn(png_structrp png_ptr, png_voidp io_ptr,
    102    png_rw_ptr read_data_fn)
    103 {
    104    if (png_ptr == NULL)
    105       return;
    106 
    107    png_ptr->io_ptr = io_ptr;
    108 
    109 #ifdef PNG_STDIO_SUPPORTED
    110    if (read_data_fn != NULL)
    111       png_ptr->read_data_fn = read_data_fn;
    112 
    113    else
    114       png_ptr->read_data_fn = png_default_read_data;
    115 #else
    116    png_ptr->read_data_fn = read_data_fn;
    117 #endif
    118 
    119 #ifdef PNG_WRITE_SUPPORTED
    120    /* It is an error to write to a read device */
    121    if (png_ptr->write_data_fn != NULL)
    122    {
    123       png_ptr->write_data_fn = NULL;
    124       png_warning(png_ptr,
    125           "Can't set both read_data_fn and write_data_fn in the"
    126           " same structure");
    127    }
    128 #endif
    129 
    130 #ifdef PNG_WRITE_FLUSH_SUPPORTED
    131    png_ptr->output_flush_fn = NULL;
    132 #endif
    133 }
    134 
    135 #ifdef PNG_INDEX_SUPPORTED
    136 void PNGAPI
    137 png_set_seek_fn(png_structp png_ptr, png_seek_ptr seek_data_fn)
    138 {
    139    if (png_ptr == NULL)
    140       return;
    141    png_ptr->seek_data_fn = seek_data_fn;
    142 }
    143 #endif
    144 
    145 #endif /* PNG_READ_SUPPORTED */
    146