pngwio.c (5588B)
1 /* pngwio.c - functions for data output 2 * 3 * Copyright (c) 2018-2025 Cosmin Truta 4 * Copyright (c) 1998-2002,2004,2006-2014,2016,2018 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 output. Users who need 13 * special handling are expected to write functions that have the same 14 * arguments as these and perform similar functions, but that possibly 15 * use different output methods. Note that you shouldn't change these 16 * functions, but rather write replacement functions and then change 17 * them at run time with png_set_write_fn(...). 18 */ 19 20 #include "pngpriv.h" 21 22 #ifdef PNG_WRITE_SUPPORTED 23 24 /* Write the data to whatever output you are using. The default routine 25 * writes to 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 writes. This should never be asked 28 * to write more than 64K on a 16-bit machine. 29 */ 30 31 void /* PRIVATE */ 32 png_write_data(png_structrp png_ptr, png_const_bytep data, size_t length) 33 { 34 /* NOTE: write_data_fn must not change the buffer! */ 35 if (png_ptr->write_data_fn != NULL ) 36 (*(png_ptr->write_data_fn))(png_ptr, png_constcast(png_bytep,data), 37 length); 38 39 else 40 png_error(png_ptr, "Call to NULL write function"); 41 } 42 43 #ifdef PNG_STDIO_SUPPORTED 44 /* This is the function that does the actual writing of data. If you are 45 * not writing to a standard C stream, you should create a replacement 46 * write_data function and use it at run time with png_set_write_fn(), rather 47 * than changing the library. 48 */ 49 void PNGCBAPI 50 png_default_write_data(png_structp png_ptr, png_bytep data, size_t length) 51 { 52 size_t check; 53 54 if (png_ptr == NULL) 55 return; 56 57 check = fwrite(data, 1, length, (FILE *)png_ptr->io_ptr); 58 59 if (check != length) 60 png_error(png_ptr, "Write Error"); 61 } 62 #endif 63 64 /* This function is called to output any data pending writing (normally 65 * to disk). After png_flush is called, there should be no data pending 66 * writing in any buffers. 67 */ 68 #ifdef PNG_WRITE_FLUSH_SUPPORTED 69 void /* PRIVATE */ 70 png_flush(png_structrp png_ptr) 71 { 72 if (png_ptr->output_flush_fn != NULL) 73 (*(png_ptr->output_flush_fn))(png_ptr); 74 } 75 76 # ifdef PNG_STDIO_SUPPORTED 77 void PNGCBAPI 78 png_default_flush(png_structp png_ptr) 79 { 80 FILE *io_ptr; 81 82 if (png_ptr == NULL) 83 return; 84 85 io_ptr = png_voidcast(FILE *, png_ptr->io_ptr); 86 fflush(io_ptr); 87 } 88 # endif 89 #endif 90 91 /* This function allows the application to supply new output functions for 92 * libpng if standard C streams aren't being used. 93 * 94 * This function takes as its arguments: 95 * png_ptr - pointer to a png output data structure 96 * io_ptr - pointer to user supplied structure containing info about 97 * the output functions. May be NULL. 98 * write_data_fn - pointer to a new output function that takes as its 99 * arguments a pointer to a png_struct, a pointer to 100 * data to be written, and a 32-bit unsigned int that is 101 * the number of bytes to be written. The new write 102 * function should call png_error(png_ptr, "Error msg") 103 * to exit and output any fatal error messages. May be 104 * NULL, in which case libpng's default function will 105 * be used. 106 * flush_data_fn - pointer to a new flush function that takes as its 107 * arguments a pointer to a png_struct. After a call to 108 * the flush function, there should be no data in any buffers 109 * or pending transmission. If the output method doesn't do 110 * any buffering of output, a function prototype must still be 111 * supplied although it doesn't have to do anything. If 112 * PNG_WRITE_FLUSH_SUPPORTED is not defined at libpng compile 113 * time, output_flush_fn will be ignored, although it must be 114 * supplied for compatibility. May be NULL, in which case 115 * libpng's default function will be used, if 116 * PNG_WRITE_FLUSH_SUPPORTED is defined. This is not 117 * a good idea if io_ptr does not point to a standard 118 * *FILE structure. 119 */ 120 void PNGAPI 121 png_set_write_fn(png_structrp png_ptr, png_voidp io_ptr, 122 png_rw_ptr write_data_fn, png_flush_ptr output_flush_fn) 123 { 124 if (png_ptr == NULL) 125 return; 126 127 png_ptr->io_ptr = io_ptr; 128 129 #ifdef PNG_STDIO_SUPPORTED 130 if (write_data_fn != NULL) 131 png_ptr->write_data_fn = write_data_fn; 132 133 else 134 png_ptr->write_data_fn = png_default_write_data; 135 #else 136 png_ptr->write_data_fn = write_data_fn; 137 #endif 138 139 #ifdef PNG_WRITE_FLUSH_SUPPORTED 140 # ifdef PNG_STDIO_SUPPORTED 141 142 if (output_flush_fn != NULL) 143 png_ptr->output_flush_fn = output_flush_fn; 144 145 else 146 png_ptr->output_flush_fn = png_default_flush; 147 148 # else 149 png_ptr->output_flush_fn = output_flush_fn; 150 # endif 151 #else 152 PNG_UNUSED(output_flush_fn) 153 #endif /* WRITE_FLUSH */ 154 155 #ifdef PNG_READ_SUPPORTED 156 /* It is an error to read while writing a png file */ 157 if (png_ptr->read_data_fn != NULL) 158 { 159 png_ptr->read_data_fn = NULL; 160 161 png_warning(png_ptr, 162 "Can't set both read_data_fn and write_data_fn in the" 163 " same structure"); 164 } 165 #endif 166 } 167 #endif /* WRITE */