1 
2 /* pngrio.c - functions for data input
3  *
4  * Copyright (c) 2018 Cosmin Truta
5  * Copyright (c) 1998-2002,2004,2006-2016,2018 Glenn Randers-Pehrson
6  * Copyright (c) 1996-1997 Andreas Dilger
7  * 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 than 64K on a 16-bit machine.
30  */
31 void /* PRIVATE */
png_read_data(png_structrp png_ptr,png_bytep data,size_t length)32 png_read_data(png_structrp png_ptr, png_bytep data, 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 }
42 
43 #ifdef PNG_STDIO_SUPPORTED
44 /* This is the function that does the actual reading of data.  If you are
45  * not reading from a standard C stream, you should create a replacement
46  * read_data function and use it at run time with png_set_read_fn(), rather
47  * than changing the library.
48  */
49 void PNGCBAPI
png_default_read_data(png_structp png_ptr,png_bytep data,size_t length)50 png_default_read_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    /* fread() returns 0 on error, so it is OK to store this in a size_t
58     * instead of an int, which is what fread() actually returns.
59     */
60    check = fread(data, 1, length, png_voidcast(png_FILE_p, png_ptr->io_ptr));
61 
62    if (check != length)
63       png_error(png_ptr, "Read Error");
64 }
65 #endif
66 
67 /* This function allows the application to supply a new input function
68  * for libpng if standard C streams aren't being used.
69  *
70  * This function takes as its arguments:
71  *
72  * png_ptr      - pointer to a png input data structure
73  *
74  * io_ptr       - pointer to user supplied structure containing info about
75  *                the input functions.  May be NULL.
76  *
77  * read_data_fn - pointer to a new input function that takes as its
78  *                arguments a pointer to a png_struct, a pointer to
79  *                a location where input data can be stored, and a 32-bit
80  *                unsigned int that is the number of bytes to be read.
81  *                To exit and output any fatal error messages the new write
82  *                function should call png_error(png_ptr, "Error msg").
83  *                May be NULL, in which case libpng's default function will
84  *                be used.
85  */
86 void PNGAPI
png_set_read_fn(png_structrp png_ptr,png_voidp io_ptr,png_rw_ptr read_data_fn)87 png_set_read_fn(png_structrp png_ptr, png_voidp io_ptr,
88     png_rw_ptr read_data_fn)
89 {
90    if (png_ptr == NULL)
91       return;
92 
93    png_ptr->io_ptr = io_ptr;
94 
95 #ifdef PNG_STDIO_SUPPORTED
96    if (read_data_fn != NULL)
97       png_ptr->read_data_fn = read_data_fn;
98 
99    else
100       png_ptr->read_data_fn = png_default_read_data;
101 #else
102    png_ptr->read_data_fn = read_data_fn;
103 #endif
104 
105 #ifdef PNG_WRITE_SUPPORTED
106    /* It is an error to write to a read device */
107    if (png_ptr->write_data_fn != NULL)
108    {
109       png_ptr->write_data_fn = NULL;
110       png_warning(png_ptr,
111           "Can't set both read_data_fn and write_data_fn in the"
112           " same structure");
113    }
114 #endif
115 
116 #ifdef PNG_WRITE_FLUSH_SUPPORTED
117    png_ptr->output_flush_fn = NULL;
118 #endif
119 }
120 #endif /* READ */
121