1/* pngrio.c - functions for data input
2 *
3 * Last changed in libpng 1.6.0 [February 14, 2013]
4 * Copyright (c) 1998-2013 Glenn Randers-Pehrson
5 * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
6 * (Version 0.88 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 then 64K on a 16 bit machine.
29 */
30void /* PRIVATE */
31png_read_data(png_structrp png_ptr, png_bytep data, png_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 */
48void PNGCBAPI
49png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
50{
51   png_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 png_size_t
57    * instead of an int, which is what fread() actually returns.
58    */
59   check = fread(data, 1, length, png_voidcast(png_FILE_p, 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 */
85void PNGAPI
86png_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   /* It is an error to write to a read device */
105   if (png_ptr->write_data_fn != NULL)
106   {
107      png_ptr->write_data_fn = NULL;
108      png_warning(png_ptr,
109          "Can't set both read_data_fn and write_data_fn in the"
110          " same structure");
111   }
112
113#ifdef PNG_WRITE_FLUSH_SUPPORTED
114   png_ptr->output_flush_fn = NULL;
115#endif
116}
117#endif /* PNG_READ_SUPPORTED */
118