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1 
2 /* pngwio.c - functions for data output
3  *
4  * Last changed in libpng 1.6.15 [November 20, 2014]
5  * Copyright (c) 1998-2002,2004,2006-2014 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 output.  Users who need
14  * special handling are expected to write functions that have the same
15  * arguments as these and perform similar functions, but that possibly
16  * use different output methods.  Note that you shouldn't change these
17  * functions, but rather write replacement functions and then change
18  * them at run time with png_set_write_fn(...).
19  */
20 
21 #include "pngpriv.h"
22 
23 #ifdef PNG_WRITE_SUPPORTED
24 
25 /* Write the data to whatever output you are using.  The default routine
26  * writes to 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 writes.  This should never be asked
29  * to write more than 64K on a 16-bit machine.
30  */
31 
32 void /* PRIVATE */
png_write_data(png_structrp png_ptr,png_const_bytep data,png_size_t length)33 png_write_data(png_structrp png_ptr, png_const_bytep data, png_size_t length)
34 {
35    /* NOTE: write_data_fn must not change the buffer! */
36    if (png_ptr->write_data_fn != NULL )
37       (*(png_ptr->write_data_fn))(png_ptr, png_constcast(png_bytep,data),
38          length);
39 
40    else
41       png_error(png_ptr, "Call to NULL write function");
42 }
43 
44 #ifdef PNG_STDIO_SUPPORTED
45 /* This is the function that does the actual writing of data.  If you are
46  * not writing to a standard C stream, you should create a replacement
47  * write_data function and use it at run time with png_set_write_fn(), rather
48  * than changing the library.
49  */
50 void PNGCBAPI
png_default_write_data(png_structp png_ptr,png_bytep data,png_size_t length)51 png_default_write_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 
58    check = fwrite(data, 1, length, (png_FILE_p)(png_ptr->io_ptr));
59 
60    if (check != length)
61       png_error(png_ptr, "Write Error");
62 }
63 #endif
64 
65 /* This function is called to output any data pending writing (normally
66  * to disk).  After png_flush is called, there should be no data pending
67  * writing in any buffers.
68  */
69 #ifdef PNG_WRITE_FLUSH_SUPPORTED
70 void /* PRIVATE */
png_flush(png_structrp png_ptr)71 png_flush(png_structrp png_ptr)
72 {
73    if (png_ptr->output_flush_fn != NULL)
74       (*(png_ptr->output_flush_fn))(png_ptr);
75 }
76 
77 #  ifdef PNG_STDIO_SUPPORTED
78 void PNGCBAPI
png_default_flush(png_structp png_ptr)79 png_default_flush(png_structp png_ptr)
80 {
81    png_FILE_p io_ptr;
82 
83    if (png_ptr == NULL)
84       return;
85 
86    io_ptr = png_voidcast(png_FILE_p, (png_ptr->io_ptr));
87    fflush(io_ptr);
88 }
89 #  endif
90 #endif
91 
92 /* This function allows the application to supply new output functions for
93  * libpng if standard C streams aren't being used.
94  *
95  * This function takes as its arguments:
96  * png_ptr       - pointer to a png output data structure
97  * io_ptr        - pointer to user supplied structure containing info about
98  *                 the output functions.  May be NULL.
99  * write_data_fn - pointer to a new output function that takes as its
100  *                 arguments a pointer to a png_struct, a pointer to
101  *                 data to be written, and a 32-bit unsigned int that is
102  *                 the number of bytes to be written.  The new write
103  *                 function should call png_error(png_ptr, "Error msg")
104  *                 to exit and output any fatal error messages.  May be
105  *                 NULL, in which case libpng's default function will
106  *                 be used.
107  * flush_data_fn - pointer to a new flush function that takes as its
108  *                 arguments a pointer to a png_struct.  After a call to
109  *                 the flush function, there should be no data in any buffers
110  *                 or pending transmission.  If the output method doesn't do
111  *                 any buffering of output, a function prototype must still be
112  *                 supplied although it doesn't have to do anything.  If
113  *                 PNG_WRITE_FLUSH_SUPPORTED is not defined at libpng compile
114  *                 time, output_flush_fn will be ignored, although it must be
115  *                 supplied for compatibility.  May be NULL, in which case
116  *                 libpng's default function will be used, if
117  *                 PNG_WRITE_FLUSH_SUPPORTED is defined.  This is not
118  *                 a good idea if io_ptr does not point to a standard
119  *                 *FILE structure.
120  */
121 void PNGAPI
png_set_write_fn(png_structrp png_ptr,png_voidp io_ptr,png_rw_ptr write_data_fn,png_flush_ptr output_flush_fn)122 png_set_write_fn(png_structrp png_ptr, png_voidp io_ptr,
123     png_rw_ptr write_data_fn, png_flush_ptr output_flush_fn)
124 {
125    if (png_ptr == NULL)
126       return;
127 
128    png_ptr->io_ptr = io_ptr;
129 
130 #ifdef PNG_STDIO_SUPPORTED
131    if (write_data_fn != NULL)
132       png_ptr->write_data_fn = write_data_fn;
133 
134    else
135       png_ptr->write_data_fn = png_default_write_data;
136 #else
137    png_ptr->write_data_fn = write_data_fn;
138 #endif
139 
140 #ifdef PNG_WRITE_FLUSH_SUPPORTED
141 #  ifdef PNG_STDIO_SUPPORTED
142 
143    if (output_flush_fn != NULL)
144       png_ptr->output_flush_fn = output_flush_fn;
145 
146    else
147       png_ptr->output_flush_fn = png_default_flush;
148 
149 #  else
150    png_ptr->output_flush_fn = output_flush_fn;
151 #  endif
152 #else
153    PNG_UNUSED(output_flush_fn)
154 #endif /* WRITE_FLUSH */
155 
156 #ifdef PNG_READ_SUPPORTED
157    /* It is an error to read while writing a png file */
158    if (png_ptr->read_data_fn != NULL)
159    {
160       png_ptr->read_data_fn = NULL;
161 
162       png_warning(png_ptr,
163           "Can't set both read_data_fn and write_data_fn in the"
164           " same structure");
165    }
166 #endif
167 }
168 #endif /* WRITE */
169