pngrio.c 3.8 KB

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  1. /* pngrio.c - functions for data input
  2. *
  3. * Copyright (c) 2018 Cosmin Truta
  4. * Copyright (c) 1998-2002,2004,2006-2016,2018 Glenn Randers-Pehrson
  5. * Copyright (c) 1996-1997 Andreas Dilger
  6. * 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. #include "pngpriv.h"
  20. #ifdef PNG_READ_SUPPORTED
  21. /* Read the data from whatever input you are using. The default routine
  22. * reads from a file pointer. Note that this routine sometimes gets called
  23. * with very small lengths, so you should implement some kind of simple
  24. * buffering if you are using unbuffered reads. This should never be asked
  25. * to read more than 64K on a 16-bit machine.
  26. */
  27. void /* PRIVATE */
  28. png_read_data(png_structrp png_ptr, png_bytep data, size_t length)
  29. {
  30. png_debug1(4, "reading %d bytes", (int)length);
  31. if (png_ptr->read_data_fn != NULL)
  32. (*(png_ptr->read_data_fn))(png_ptr, data, length);
  33. else
  34. png_error(png_ptr, "Call to NULL read function");
  35. }
  36. #ifdef PNG_STDIO_SUPPORTED
  37. /* This is the function that does the actual reading of data. If you are
  38. * not reading from a standard C stream, you should create a replacement
  39. * read_data function and use it at run time with png_set_read_fn(), rather
  40. * than changing the library.
  41. */
  42. void PNGCBAPI
  43. png_default_read_data(png_structp png_ptr, png_bytep data, size_t length)
  44. {
  45. size_t check;
  46. if (png_ptr == NULL)
  47. return;
  48. /* fread() returns 0 on error, so it is OK to store this in a size_t
  49. * instead of an int, which is what fread() actually returns.
  50. */
  51. check = fread(data, 1, length, png_voidcast(png_FILE_p, png_ptr->io_ptr));
  52. if (check != length)
  53. png_error(png_ptr, "Read Error");
  54. }
  55. #endif
  56. /* This function allows the application to supply a new input function
  57. * for libpng if standard C streams aren't being used.
  58. *
  59. * This function takes as its arguments:
  60. *
  61. * png_ptr - pointer to a png input data structure
  62. *
  63. * io_ptr - pointer to user supplied structure containing info about
  64. * the input functions. May be NULL.
  65. *
  66. * read_data_fn - pointer to a new input function that takes as its
  67. * arguments a pointer to a png_struct, a pointer to
  68. * a location where input data can be stored, and a 32-bit
  69. * unsigned int that is the number of bytes to be read.
  70. * To exit and output any fatal error messages the new write
  71. * function should call png_error(png_ptr, "Error msg").
  72. * May be NULL, in which case libpng's default function will
  73. * be used.
  74. */
  75. void PNGAPI
  76. png_set_read_fn(png_structrp png_ptr, png_voidp io_ptr,
  77. png_rw_ptr read_data_fn)
  78. {
  79. if (png_ptr == NULL)
  80. return;
  81. png_ptr->io_ptr = io_ptr;
  82. #ifdef PNG_STDIO_SUPPORTED
  83. if (read_data_fn != NULL)
  84. png_ptr->read_data_fn = read_data_fn;
  85. else
  86. png_ptr->read_data_fn = png_default_read_data;
  87. #else
  88. png_ptr->read_data_fn = read_data_fn;
  89. #endif
  90. #ifdef PNG_WRITE_SUPPORTED
  91. /* It is an error to write to a read device */
  92. if (png_ptr->write_data_fn != NULL)
  93. {
  94. png_ptr->write_data_fn = NULL;
  95. png_warning(png_ptr,
  96. "Can't set both read_data_fn and write_data_fn in the"
  97. " same structure");
  98. }
  99. #endif
  100. #ifdef PNG_WRITE_FLUSH_SUPPORTED
  101. png_ptr->output_flush_fn = NULL;
  102. #endif
  103. }
  104. #endif /* READ */