1 2/* pngrio.c - functions for data input 3 * 4 * Last changed in libpng 1.4.1 [February 25, 2010] 5 * Copyright (c) 1998-2010 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#define PNG_NO_PEDANTIC_WARNINGS 22#include "png.h" 23#ifdef PNG_READ_SUPPORTED 24#include "pngpriv.h" 25 26/* Read the data from whatever input you are using. The default routine 27 * reads from a file pointer. Note that this routine sometimes gets called 28 * with very small lengths, so you should implement some kind of simple 29 * buffering if you are using unbuffered reads. This should never be asked 30 * to read more then 64K on a 16 bit machine. 31 */ 32void /* PRIVATE */ 33png_read_data(png_structp png_ptr, png_bytep data, png_size_t length) 34{ 35 png_debug1(4, "reading %d bytes", (int)length); 36 37 if (png_ptr->read_data_fn != NULL) 38 (*(png_ptr->read_data_fn))(png_ptr, data, length); 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#ifndef USE_FAR_KEYWORD 50void PNGAPI 51png_default_read_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 /* 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_FILE_p)png_ptr->io_ptr); 61 62 if (check != length) 63 png_error(png_ptr, "Read Error"); 64} 65#else 66/* This is the model-independent version. Since the standard I/O library 67 can't handle far buffers in the medium and small models, we have to copy 68 the data. 69*/ 70 71#define NEAR_BUF_SIZE 1024 72#define MIN(a,b) (a <= b ? a : b) 73 74static void PNGAPI 75png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length) 76{ 77 png_size_t check; 78 png_byte *n_data; 79 png_FILE_p io_ptr; 80 81 if (png_ptr == NULL) 82 return; 83 /* Check if data really is near. If so, use usual code. */ 84 n_data = (png_byte *)CVT_PTR_NOCHECK(data); 85 io_ptr = (png_FILE_p)CVT_PTR(png_ptr->io_ptr); 86 if ((png_bytep)n_data == data) 87 { 88 check = fread(n_data, 1, length, io_ptr); 89 } 90 else 91 { 92 png_byte buf[NEAR_BUF_SIZE]; 93 png_size_t read, remaining, err; 94 check = 0; 95 remaining = length; 96 do 97 { 98 read = MIN(NEAR_BUF_SIZE, remaining); 99 err = fread(buf, 1, read, io_ptr); 100 png_memcpy(data, buf, read); /* copy far buffer to near buffer */ 101 if (err != read) 102 break; 103 else 104 check += err; 105 data += read; 106 remaining -= read; 107 } 108 while (remaining != 0); 109 } 110 if ((png_uint_32)check != (png_uint_32)length) 111 png_error(png_ptr, "read Error"); 112} 113#endif 114#endif 115 116/* This function allows the application to supply a new input function 117 * for libpng if standard C streams aren't being used. 118 * 119 * This function takes as its arguments: 120 * png_ptr - pointer to a png input data structure 121 * io_ptr - pointer to user supplied structure containing info about 122 * the input functions. May be NULL. 123 * read_data_fn - pointer to a new input function that takes as its 124 * arguments a pointer to a png_struct, a pointer to 125 * a location where input data can be stored, and a 32-bit 126 * unsigned int that is the number of bytes to be read. 127 * To exit and output any fatal error messages the new write 128 * function should call png_error(png_ptr, "Error msg"). 129 * May be NULL, in which case libpng's default function will 130 * be used. 131 */ 132void PNGAPI 133png_set_read_fn(png_structp png_ptr, png_voidp io_ptr, 134 png_rw_ptr read_data_fn) 135{ 136 if (png_ptr == NULL) 137 return; 138 png_ptr->io_ptr = io_ptr; 139 140#ifdef PNG_STDIO_SUPPORTED 141 if (read_data_fn != NULL) 142 png_ptr->read_data_fn = read_data_fn; 143 else 144 png_ptr->read_data_fn = png_default_read_data; 145#else 146 png_ptr->read_data_fn = read_data_fn; 147#endif 148 149 /* It is an error to write to a read device */ 150 if (png_ptr->write_data_fn != NULL) 151 { 152 png_ptr->write_data_fn = NULL; 153 png_warning(png_ptr, 154 "It's an error to set both read_data_fn and write_data_fn in the "); 155 png_warning(png_ptr, 156 "same structure. Resetting write_data_fn to NULL"); 157 } 158 159#ifdef PNG_WRITE_FLUSH_SUPPORTED 160 png_ptr->output_flush_fn = NULL; 161#endif 162} 163#endif /* PNG_READ_SUPPORTED */ 164