pngrio.c 3.9 KB
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/* pngrio.c - functions for data input
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 *
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 * Last changed in libpng 1.6.35 [July 15, 2018]
 * Copyright (c) 1998-2002,2004,2006-2016,2018 Glenn Randers-Pehrson
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 * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
 * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
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 *
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 * This code is released under the libpng license.
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 * For conditions of distribution and use, see the disclaimer
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 * and license in png.h
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 *
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 * This file provides a location for all input.  Users who need
 * special handling are expected to write a function that has the same
 * arguments as this and performs a similar function, but that possibly
 * has a different input method.  Note that you shouldn't change this
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 * function, but rather write a replacement function and then make
 * libpng use it at run time with png_set_read_fn(...).
 */
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#include "pngpriv.h"
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#ifdef PNG_READ_SUPPORTED

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/* Read the data from whatever input you are using.  The default routine
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 * reads from a file pointer.  Note that this routine sometimes gets called
 * with very small lengths, so you should implement some kind of simple
 * buffering if you are using unbuffered reads.  This should never be asked
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 * to read more than 64K on a 16-bit machine.
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 */
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void /* PRIVATE */
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png_read_data(png_structrp png_ptr, png_bytep data, size_t length)
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{
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   png_debug1(4, "reading %d bytes", (int)length);
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   if (png_ptr->read_data_fn != NULL)
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      (*(png_ptr->read_data_fn))(png_ptr, data, length);
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   else
      png_error(png_ptr, "Call to NULL read function");
}

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#ifdef PNG_STDIO_SUPPORTED
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/* This is the function that does the actual reading of data.  If you are
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 * not reading from a standard C stream, you should create a replacement
 * read_data function and use it at run time with png_set_read_fn(), rather
 * than changing the library.
 */
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void PNGCBAPI
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png_default_read_data(png_structp png_ptr, png_bytep data, size_t length)
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{
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   size_t check;
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   if (png_ptr == NULL)
      return;
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   /* fread() returns 0 on error, so it is OK to store this in a size_t
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    * instead of an int, which is what fread() actually returns.
    */
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   check = fread(data, 1, length, png_voidcast(png_FILE_p, png_ptr->io_ptr));
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   if (check != length)
      png_error(png_ptr, "Read Error");
}
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#endif
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/* This function allows the application to supply a new input function
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 * for libpng if standard C streams aren't being used.
 *
 * This function takes as its arguments:
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 *
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 * png_ptr      - pointer to a png input data structure
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 *
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 * io_ptr       - pointer to user supplied structure containing info about
 *                the input functions.  May be NULL.
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 *
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 * read_data_fn - pointer to a new input function that takes as its
 *                arguments a pointer to a png_struct, a pointer to
 *                a location where input data can be stored, and a 32-bit
 *                unsigned int that is the number of bytes to be read.
 *                To exit and output any fatal error messages the new write
 *                function should call png_error(png_ptr, "Error msg").
 *                May be NULL, in which case libpng's default function will
 *                be used.
 */
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void PNGAPI
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png_set_read_fn(png_structrp png_ptr, png_voidp io_ptr,
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    png_rw_ptr read_data_fn)
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{
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   if (png_ptr == NULL)
      return;
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   png_ptr->io_ptr = io_ptr;

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#ifdef PNG_STDIO_SUPPORTED
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   if (read_data_fn != NULL)
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      png_ptr->read_data_fn = read_data_fn;
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   else
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      png_ptr->read_data_fn = png_default_read_data;
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#else
   png_ptr->read_data_fn = read_data_fn;
#endif
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#ifdef PNG_WRITE_SUPPORTED
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   /* It is an error to write to a read device */
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   if (png_ptr->write_data_fn != NULL)
   {
      png_ptr->write_data_fn = NULL;
      png_warning(png_ptr,
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          "Can't set both read_data_fn and write_data_fn in the"
          " same structure");
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   }
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#endif
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#ifdef PNG_WRITE_FLUSH_SUPPORTED
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   png_ptr->output_flush_fn = NULL;
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#endif
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}
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#endif /* READ */