1 /*
   2  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   3  *
   4  * This code is free software; you can redistribute it and/or modify it
   5  * under the terms of the GNU General Public License version 2 only, as
   6  * published by the Free Software Foundation.  Oracle designates this
   7  * particular file as subject to the "Classpath" exception as provided
   8  * by Oracle in the LICENSE file that accompanied this code.
   9  *
  10  * This code is distributed in the hope that it will be useful, but WITHOUT
  11  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  12  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  13  * version 2 for more details (a copy is included in the LICENSE file that
  14  * accompanied this code).
  15  *
  16  * You should have received a copy of the GNU General Public License version
  17  * 2 along with this work; if not, write to the Free Software Foundation,
  18  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  19  *
  20  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  21  * or visit www.oracle.com if you need additional information or have any
  22  * questions.
  23  */
  24 
  25 /* pngrio.c - functions for data input
  26  *
  27  * Copyright (c) 2018 Cosmin Truta
  28  * Copyright (c) 1998-2002,2004,2006-2016,2018 Glenn Randers-Pehrson
  29  * Copyright (c) 1996-1997 Andreas Dilger
  30  * Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc.
  31  *
  32  * This code is released under the libpng license.
  33  * For conditions of distribution and use, see the disclaimer
  34  * and license in png.h
  35  *
  36  * This file provides a location for all input.  Users who need
  37  * special handling are expected to write a function that has the same
  38  * arguments as this and performs a similar function, but that possibly
  39  * has a different input method.  Note that you shouldn't change this
  40  * function, but rather write a replacement function and then make
  41  * libpng use it at run time with png_set_read_fn(...).
  42  */
  43 
  44 #include "pngpriv.h"
  45 
  46 #ifdef PNG_READ_SUPPORTED
  47 
  48 /* Read the data from whatever input you are using.  The default routine
  49  * reads from a file pointer.  Note that this routine sometimes gets called
  50  * with very small lengths, so you should implement some kind of simple
  51  * buffering if you are using unbuffered reads.  This should never be asked
  52  * to read more than 64K on a 16-bit machine.
  53  */
  54 void /* PRIVATE */
  55 png_read_data(png_structrp png_ptr, png_bytep data, size_t length)
  56 {
  57    png_debug1(4, "reading %d bytes", (int)length);
  58 
  59    if (png_ptr->read_data_fn != NULL)
  60       (*(png_ptr->read_data_fn))(png_ptr, data, length);
  61 
  62    else
  63       png_error(png_ptr, "Call to NULL read function");
  64 }
  65 
  66 #ifdef PNG_STDIO_SUPPORTED
  67 /* This is the function that does the actual reading of data.  If you are
  68  * not reading from a standard C stream, you should create a replacement
  69  * read_data function and use it at run time with png_set_read_fn(), rather
  70  * than changing the library.
  71  */
  72 void PNGCBAPI
  73 png_default_read_data(png_structp png_ptr, png_bytep data, size_t length)
  74 {
  75    size_t check;
  76 
  77    if (png_ptr == NULL)
  78       return;
  79 
  80    /* fread() returns 0 on error, so it is OK to store this in a size_t
  81     * instead of an int, which is what fread() actually returns.
  82     */
  83    check = fread(data, 1, length, png_voidcast(png_FILE_p, png_ptr->io_ptr));
  84 
  85    if (check != length)
  86       png_error(png_ptr, "Read Error");
  87 }
  88 #endif
  89 
  90 /* This function allows the application to supply a new input function
  91  * for libpng if standard C streams aren't being used.
  92  *
  93  * This function takes as its arguments:
  94  *
  95  * png_ptr      - pointer to a png input data structure
  96  *
  97  * io_ptr       - pointer to user supplied structure containing info about
  98  *                the input functions.  May be NULL.
  99  *
 100  * read_data_fn - pointer to a new input function that takes as its
 101  *                arguments a pointer to a png_struct, a pointer to
 102  *                a location where input data can be stored, and a 32-bit
 103  *                unsigned int that is the number of bytes to be read.
 104  *                To exit and output any fatal error messages the new write
 105  *                function should call png_error(png_ptr, "Error msg").
 106  *                May be NULL, in which case libpng's default function will
 107  *                be used.
 108  */
 109 void PNGAPI
 110 png_set_read_fn(png_structrp png_ptr, png_voidp io_ptr,
 111     png_rw_ptr read_data_fn)
 112 {
 113    if (png_ptr == NULL)
 114       return;
 115 
 116    png_ptr->io_ptr = io_ptr;
 117 
 118 #ifdef PNG_STDIO_SUPPORTED
 119    if (read_data_fn != NULL)
 120       png_ptr->read_data_fn = read_data_fn;
 121 
 122    else
 123       png_ptr->read_data_fn = png_default_read_data;
 124 #else
 125    png_ptr->read_data_fn = read_data_fn;
 126 #endif
 127 
 128 #ifdef PNG_WRITE_SUPPORTED
 129    /* It is an error to write to a read device */
 130    if (png_ptr->write_data_fn != NULL)
 131    {
 132       png_ptr->write_data_fn = NULL;
 133       png_warning(png_ptr,
 134           "Can't set both read_data_fn and write_data_fn in the"
 135           " same structure");
 136    }
 137 #endif
 138 
 139 #ifdef PNG_WRITE_FLUSH_SUPPORTED
 140    png_ptr->output_flush_fn = NULL;
 141 #endif
 142 }
 143 #endif /* READ */