pngrio.c revision 893912bfc2683463dc3e2c445336752d012563d3 
1
2/* pngrio.c - functions for data input
3 *
4 * Last changed in libpng 1.2.13 November 13, 2006
5 * For conditions of distribution and use, see copyright notice in png.h
6 * Copyright (c) 1998-2006 Glenn Randers-Pehrson
7 * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
8 * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
9 *
10 * This file provides a location for all input.  Users who need
11 * special handling are expected to write a function that has the same
12 * arguments as this and performs a similar function, but that possibly
13 * has a different input method.  Note that you shouldn't change this
14 * function, but rather write a replacement function and then make
15 * libpng use it at run time with png_set_read_fn(...).
16 */
17
18#define PNG_INTERNAL
19#include "png.h"
20
21#if defined(PNG_READ_SUPPORTED)
22
23/* Read the data from whatever input you are using.  The default routine
24   reads from a file pointer.  Note that this routine sometimes gets called
25   with very small lengths, so you should implement some kind of simple
26   buffering if you are using unbuffered reads.  This should never be asked
27   to read more then 64K on a 16 bit machine. */
28void /* PRIVATE */
29png_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
30{
31   png_debug1(4,"reading %d bytes\n", (int)length);
32   if (png_ptr->read_data_fn != NULL)
33      (*(png_ptr->read_data_fn))(png_ptr, data, length);
34   else
35      png_error(png_ptr, "Call to NULL read function");
36}
37
38#if !defined(PNG_NO_STDIO)
39/* This is the function that does the actual reading of data.  If you are
40   not reading from a standard C stream, you should create a replacement
41   read_data function and use it at run time with png_set_read_fn(), rather
42   than changing the library. */
43#ifndef USE_FAR_KEYWORD
44void PNGAPI
45png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
46{
47   png_size_t check;
48
49   if(png_ptr == NULL) return;
50   /* fread() returns 0 on error, so it is OK to store this in a png_size_t
51    * instead of an int, which is what fread() actually returns.
52    */
53#if defined(_WIN32_WCE)
54   if ( !ReadFile((HANDLE)(png_ptr->io_ptr), data, length, &check, NULL) )
55      check = 0;
56#else
57   check = (png_size_t)fread(data, (png_size_t)1, length,
58      (png_FILE_p)png_ptr->io_ptr);
59#endif
60
61   if (check != length)
62      png_error(png_ptr, "Read Error");
63}
64#else
65/* this is the model-independent version. Since the standard I/O library
66   can't handle far buffers in the medium and small models, we have to copy
67   the data.
68*/
69
70#define NEAR_BUF_SIZE 1024
71#define MIN(a,b) (a <= b ? a : b)
72
73static void PNGAPI
74png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
75{
76   int check;
77   png_byte *n_data;
78   png_FILE_p io_ptr;
79
80   if(png_ptr == NULL) return;
81   /* Check if data really is near. If so, use usual code. */
82   n_data = (png_byte *)CVT_PTR_NOCHECK(data);
83   io_ptr = (png_FILE_p)CVT_PTR(png_ptr->io_ptr);
84   if ((png_bytep)n_data == data)
85   {
86#if defined(_WIN32_WCE)
87      if ( !ReadFile((HANDLE)(png_ptr->io_ptr), data, length, &check, NULL) )
88         check = 0;
89#else
90      check = fread(n_data, 1, length, io_ptr);
91#endif
92   }
93   else
94   {
95      png_byte buf[NEAR_BUF_SIZE];
96      png_size_t read, remaining, err;
97      check = 0;
98      remaining = length;
99      do
100      {
101         read = MIN(NEAR_BUF_SIZE, remaining);
102#if defined(_WIN32_WCE)
103         if ( !ReadFile((HANDLE)(io_ptr), buf, read, &err, NULL) )
104            err = 0;
105#else
106         err = fread(buf, (png_size_t)1, read, io_ptr);
107#endif
108         png_memcpy(data, buf, read); /* copy far buffer to near buffer */
109         if(err != read)
110            break;
111         else
112            check += err;
113         data += read;
114         remaining -= read;
115      }
116      while (remaining != 0);
117   }
118   if ((png_uint_32)check != (png_uint_32)length)
119      png_error(png_ptr, "read Error");
120}
121#endif
122#endif
123
124/* This function allows the application to supply a new input function
125   for libpng if standard C streams aren't being used.
126
127   This function takes as its arguments:
128   png_ptr      - pointer to a png input data structure
129   io_ptr       - pointer to user supplied structure containing info about
130                  the input functions.  May be NULL.
131   read_data_fn - pointer to a new input function that takes as its
132                  arguments a pointer to a png_struct, a pointer to
133                  a location where input data can be stored, and a 32-bit
134                  unsigned int that is the number of bytes to be read.
135                  To exit and output any fatal error messages the new write
136                  function should call png_error(png_ptr, "Error msg"). */
137void PNGAPI
138png_set_read_fn(png_structp png_ptr, png_voidp io_ptr,
139   png_rw_ptr read_data_fn)
140{
141   if(png_ptr == NULL) return;
142   png_ptr->io_ptr = io_ptr;
143
144#if !defined(PNG_NO_STDIO)
145   if (read_data_fn != NULL)
146      png_ptr->read_data_fn = read_data_fn;
147   else
148      png_ptr->read_data_fn = png_default_read_data;
149#else
150   png_ptr->read_data_fn = read_data_fn;
151#endif
152
153   /* It is an error to write to a read device */
154   if (png_ptr->write_data_fn != NULL)
155   {
156      png_ptr->write_data_fn = NULL;
157      png_warning(png_ptr,
158         "It's an error to set both read_data_fn and write_data_fn in the ");
159      png_warning(png_ptr,
160         "same structure.  Resetting write_data_fn to NULL.");
161   }
162
163#if defined(PNG_WRITE_FLUSH_SUPPORTED)
164   png_ptr->output_flush_fn = NULL;
165#endif
166}
167#endif /* PNG_READ_SUPPORTED */
168