1 2 /* pngrio.c - functions for data input 3 * 4 * Last changed in libpng 1.6.24 [August 4, 2016] 5 * Copyright (c) 1998-2002,2004,2006-2016 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 than 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 #ifdef PNG_WRITE_SUPPORTED 106 /* It is an error to write to a read device */ 107 if (png_ptr->write_data_fn != NULL) 108 { 109 png_ptr->write_data_fn = NULL; 110 png_warning(png_ptr, 111 "Can't set both read_data_fn and write_data_fn in the" 112 " same structure"); 113 } 114 #endif 115 116 #ifdef PNG_WRITE_FLUSH_SUPPORTED 117 png_ptr->output_flush_fn = NULL; 118 #endif 119 } 120 #endif /* READ */ 121
