1
2/* pngrio.c - functions for data input
3 *
4 * Last changed in libpng 1.6.9 [February 6, 2014]
5 * Copyright (c) 1998-2014 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 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 then 64K on a 16 bit machine.
30 */
31void /* PRIVATE */
32png_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#ifdef PNG_INDEX_SUPPORTED
42   png_ptr->total_data_read += length;
43#endif
44}
45
46#ifdef PNG_INDEX_SUPPORTED
47void /* PRIVATE */
48png_seek_data(png_structp png_ptr, png_uint_32 offset)
49{
50   if (png_ptr->seek_data_fn != NULL)
51      (*(png_ptr->seek_data_fn))(png_ptr, offset);
52   else
53      png_error(png_ptr, "Call to NULL seek function");
54}
55#endif
56
57#ifdef PNG_STDIO_SUPPORTED
58/* This is the function that does the actual reading of data.  If you are
59 * not reading from a standard C stream, you should create a replacement
60 * read_data function and use it at run time with png_set_read_fn(), rather
61 * than changing the library.
62 */
63void PNGCBAPI
64png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
65{
66   png_size_t check;
67
68   if (png_ptr == NULL)
69      return;
70
71   /* fread() returns 0 on error, so it is OK to store this in a png_size_t
72    * instead of an int, which is what fread() actually returns.
73    */
74   check = fread(data, 1, length, png_voidcast(png_FILE_p, png_ptr->io_ptr));
75
76   if (check != length)
77      png_error(png_ptr, "Read Error");
78}
79#endif
80
81/* This function allows the application to supply a new input function
82 * for libpng if standard C streams aren't being used.
83 *
84 * This function takes as its arguments:
85 *
86 * png_ptr      - pointer to a png input data structure
87 *
88 * io_ptr       - pointer to user supplied structure containing info about
89 *                the input functions.  May be NULL.
90 *
91 * read_data_fn - pointer to a new input function that takes as its
92 *                arguments a pointer to a png_struct, a pointer to
93 *                a location where input data can be stored, and a 32-bit
94 *                unsigned int that is the number of bytes to be read.
95 *                To exit and output any fatal error messages the new write
96 *                function should call png_error(png_ptr, "Error msg").
97 *                May be NULL, in which case libpng's default function will
98 *                be used.
99 */
100void PNGAPI
101png_set_read_fn(png_structrp png_ptr, png_voidp io_ptr,
102   png_rw_ptr read_data_fn)
103{
104   if (png_ptr == NULL)
105      return;
106
107   png_ptr->io_ptr = io_ptr;
108
109#ifdef PNG_STDIO_SUPPORTED
110   if (read_data_fn != NULL)
111      png_ptr->read_data_fn = read_data_fn;
112
113   else
114      png_ptr->read_data_fn = png_default_read_data;
115#else
116   png_ptr->read_data_fn = read_data_fn;
117#endif
118
119#ifdef PNG_WRITE_SUPPORTED
120   /* It is an error to write to a read device */
121   if (png_ptr->write_data_fn != NULL)
122   {
123      png_ptr->write_data_fn = NULL;
124      png_warning(png_ptr,
125          "Can't set both read_data_fn and write_data_fn in the"
126          " same structure");
127   }
128#endif
129
130#ifdef PNG_WRITE_FLUSH_SUPPORTED
131   png_ptr->output_flush_fn = NULL;
132#endif
133}
134
135#ifdef PNG_INDEX_SUPPORTED
136void PNGAPI
137png_set_seek_fn(png_structp png_ptr, png_seek_ptr seek_data_fn)
138{
139   if (png_ptr == NULL)
140      return;
141   png_ptr->seek_data_fn = seek_data_fn;
142}
143#endif
144
145#endif /* PNG_READ_SUPPORTED */
146