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2296
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1
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2 /* pngrio.c - functions for data input
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3 *
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4 * Last changed in libpng 1.6.9 [February 6, 2014]
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5 * Copyright (c) 1998-2014 Glenn Randers-Pehrson
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6 * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
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7 * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
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8 *
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9 * This code is released under the libpng license.
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10 * For conditions of distribution and use, see the disclaimer
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11 * and license in png.h
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12 *
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13 * This file provides a location for all input. Users who need
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14 * special handling are expected to write a function that has the same
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15 * arguments as this and performs a similar function, but that possibly
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16 * has a different input method. Note that you shouldn't change this
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17 * function, but rather write a replacement function and then make
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18 * libpng use it at run time with png_set_read_fn(...).
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19 */
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20
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21 #include "pngpriv.h"
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22
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23 #ifdef PNG_READ_SUPPORTED
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24
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25 /* Read the data from whatever input you are using. The default routine
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26 * reads from a file pointer. Note that this routine sometimes gets called
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27 * with very small lengths, so you should implement some kind of simple
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28 * buffering if you are using unbuffered reads. This should never be asked
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29 * to read more then 64K on a 16 bit machine.
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30 */
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31 void /* PRIVATE */
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32 png_read_data(png_structrp png_ptr, png_bytep data, png_size_t length)
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33 {
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34 png_debug1(4, "reading %d bytes", (int)length);
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35
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36 if (png_ptr->read_data_fn != NULL)
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37 (*(png_ptr->read_data_fn))(png_ptr, data, length);
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38
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39 else
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40 png_error(png_ptr, "Call to NULL read function");
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41 }
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42
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43 #ifdef PNG_STDIO_SUPPORTED
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44 /* This is the function that does the actual reading of data. If you are
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45 * not reading from a standard C stream, you should create a replacement
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46 * read_data function and use it at run time with png_set_read_fn(), rather
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47 * than changing the library.
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48 */
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49 void PNGCBAPI
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50 png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
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51 {
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52 png_size_t check;
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53
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54 if (png_ptr == NULL)
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55 return;
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56
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57 /* fread() returns 0 on error, so it is OK to store this in a png_size_t
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58 * instead of an int, which is what fread() actually returns.
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59 */
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60 check = fread(data, 1, length, png_voidcast(png_FILE_p, png_ptr->io_ptr));
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61
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62 if (check != length)
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63 png_error(png_ptr, "Read Error");
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64 }
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65 #endif
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66
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67 /* This function allows the application to supply a new input function
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68 * for libpng if standard C streams aren't being used.
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69 *
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70 * This function takes as its arguments:
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71 *
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72 * png_ptr - pointer to a png input data structure
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73 *
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74 * io_ptr - pointer to user supplied structure containing info about
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75 * the input functions. May be NULL.
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76 *
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77 * read_data_fn - pointer to a new input function that takes as its
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78 * arguments a pointer to a png_struct, a pointer to
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79 * a location where input data can be stored, and a 32-bit
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80 * unsigned int that is the number of bytes to be read.
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81 * To exit and output any fatal error messages the new write
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82 * function should call png_error(png_ptr, "Error msg").
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83 * May be NULL, in which case libpng's default function will
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84 * be used.
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85 */
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86 void PNGAPI
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87 png_set_read_fn(png_structrp png_ptr, png_voidp io_ptr,
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88 png_rw_ptr read_data_fn)
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89 {
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90 if (png_ptr == NULL)
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91 return;
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92
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93 png_ptr->io_ptr = io_ptr;
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94
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95 #ifdef PNG_STDIO_SUPPORTED
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96 if (read_data_fn != NULL)
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97 png_ptr->read_data_fn = read_data_fn;
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98
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99 else
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100 png_ptr->read_data_fn = png_default_read_data;
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101 #else
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102 png_ptr->read_data_fn = read_data_fn;
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103 #endif
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104
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105 #ifdef PNG_WRITE_SUPPORTED
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106 /* It is an error to write to a read device */
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107 if (png_ptr->write_data_fn != NULL)
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108 {
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109 png_ptr->write_data_fn = NULL;
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110 png_warning(png_ptr,
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111 "Can't set both read_data_fn and write_data_fn in the"
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112 " same structure");
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113 }
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114 #endif
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115
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116 #ifdef PNG_WRITE_FLUSH_SUPPORTED
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117 png_ptr->output_flush_fn = NULL;
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118 #endif
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119 }
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120 #endif /* PNG_READ_SUPPORTED */
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