pngrio.c (3898B)
1 /* pngrio.c - functions for data input 2 * 3 * Copyright (c) 2018-2025 Cosmin Truta 4 * Copyright (c) 1998-2002,2004,2006-2016,2018 Glenn Randers-Pehrson 5 * Copyright (c) 1996-1997 Andreas Dilger 6 * Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc. 7 * 8 * This code is released under the libpng license. 9 * For conditions of distribution and use, see the disclaimer 10 * and license in png.h 11 * 12 * This file provides a location for all input. Users who need 13 * special handling are expected to write a function that has the same 14 * arguments as this and performs a similar function, but that possibly 15 * has a different input method. Note that you shouldn't change this 16 * function, but rather write a replacement function and then make 17 * libpng use it at run time with png_set_read_fn(...). 18 */ 19 20 #include "pngpriv.h" 21 22 #ifdef PNG_READ_SUPPORTED 23 24 /* Read the data from whatever input you are using. The default routine 25 * reads from a file pointer. Note that this routine sometimes gets called 26 * with very small lengths, so you should implement some kind of simple 27 * buffering if you are using unbuffered reads. This should never be asked 28 * to read more than 64K on a 16-bit machine. 29 */ 30 void /* PRIVATE */ 31 png_read_data(png_structrp png_ptr, png_bytep data, size_t length) 32 { 33 png_debug1(4, "reading %d bytes", (int)length); 34 35 if (png_ptr->read_data_fn != NULL) 36 (*(png_ptr->read_data_fn))(png_ptr, data, length); 37 38 else 39 png_error(png_ptr, "Call to NULL read function"); 40 } 41 42 #ifdef PNG_STDIO_SUPPORTED 43 /* This is the function that does the actual reading of data. If you are 44 * not reading from a standard C stream, you should create a replacement 45 * read_data function and use it at run time with png_set_read_fn(), rather 46 * than changing the library. 47 */ 48 void PNGCBAPI 49 png_default_read_data(png_structp png_ptr, png_bytep data, size_t length) 50 { 51 size_t check; 52 53 if (png_ptr == NULL) 54 return; 55 56 /* fread() returns 0 on error, so it is OK to store this in a size_t 57 * instead of an int, which is what fread() actually returns. 58 */ 59 check = fread(data, 1, length, png_voidcast(FILE *, png_ptr->io_ptr)); 60 61 if (check != length) 62 png_error(png_ptr, "Read Error"); 63 } 64 #endif 65 66 /* This function allows the application to supply a new input function 67 * for libpng if standard C streams aren't being used. 68 * 69 * This function takes as its arguments: 70 * 71 * png_ptr - pointer to a png input data structure 72 * 73 * io_ptr - pointer to user supplied structure containing info about 74 * the input functions. May be NULL. 75 * 76 * read_data_fn - pointer to a new input function that takes as its 77 * arguments a pointer to a png_struct, a pointer to 78 * a location where input data can be stored, and a 32-bit 79 * unsigned int that is the number of bytes to be read. 80 * To exit and output any fatal error messages the new write 81 * function should call png_error(png_ptr, "Error msg"). 82 * May be NULL, in which case libpng's default function will 83 * be used. 84 */ 85 void PNGAPI 86 png_set_read_fn(png_structrp png_ptr, png_voidp io_ptr, 87 png_rw_ptr read_data_fn) 88 { 89 if (png_ptr == NULL) 90 return; 91 92 png_ptr->io_ptr = io_ptr; 93 94 #ifdef PNG_STDIO_SUPPORTED 95 if (read_data_fn != NULL) 96 png_ptr->read_data_fn = read_data_fn; 97 98 else 99 png_ptr->read_data_fn = png_default_read_data; 100 #else 101 png_ptr->read_data_fn = read_data_fn; 102 #endif 103 104 #ifdef PNG_WRITE_SUPPORTED 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 #endif 114 115 #ifdef PNG_WRITE_FLUSH_SUPPORTED 116 png_ptr->output_flush_fn = NULL; 117 #endif 118 } 119 #endif /* READ */