/* pngrio.c - functions for data input

 *

 * Copyright (c) 2018-2025 Cosmin Truta

 * Copyright (c) 1998-2002,2004,2006-2016,2018 Glenn Randers-Pehrson

 * Copyright (c) 1996-1997 Andreas Dilger

 * Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc.

 *

 * This code is released under the libpng license.

 * For conditions of distribution and use, see the disclaimer

 * and license in png.h

 *

 * 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

 * function, but rather write a replacement function and then make

 * libpng use it at run time with png_set_read_fn(...).

 */

#include "pngpriv.h"

#ifdef PNG_READ_SUPPORTED

/* Read the data from whatever input you are using.  The default routine

 * 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

 * to read more than 64K on a 16-bit machine.

 */

void /* PRIVATE */

png_read_data(png_structrp png_ptr, png_bytep data, size_t length)

{

   png_debug1(4, "reading %d bytes", (int)length);

   if (png_ptr->read_data_fn != NULL)

      (*(png_ptr->read_data_fn))(png_ptr, data, length);

   else

      png_error(png_ptr, "Call to NULL read function");

}

#ifdef PNG_STDIO_SUPPORTED

/* This is the function that does the actual reading of data.  If you are

 * 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.

 */

void PNGCBAPI

png_default_read_data(png_structp png_ptr, png_bytep data, size_t length)

{

   size_t check;

   if (png_ptr == NULL)

      return;

   /* fread() returns 0 on error, so it is OK to store this in a size_t

    * instead of an int, which is what fread() actually returns.

    */

   check = fread(data, 1, length, png_voidcast(FILE *, png_ptr->io_ptr));

   if (check != length)

      png_error(png_ptr, "Read Error");

}

#endif

/* This function allows the application to supply a new input function

 * for libpng if standard C streams aren't being used.

 *

 * This function takes as its arguments:

 *

 * png_ptr      - pointer to a png input data structure

 *

 * io_ptr       - pointer to user supplied structure containing info about

 *                the input functions.  May be NULL.

 *

 * 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.

 */

void PNGAPI

png_set_read_fn(png_structrp png_ptr, png_voidp io_ptr,

    png_rw_ptr read_data_fn)

{

   if (png_ptr == NULL)

      return;

   png_ptr->io_ptr = io_ptr;

#ifdef PNG_STDIO_SUPPORTED

   if (read_data_fn != NULL)

      png_ptr->read_data_fn = read_data_fn;

   else

      png_ptr->read_data_fn = png_default_read_data;

#else

   png_ptr->read_data_fn = read_data_fn;

#endif

#ifdef PNG_WRITE_SUPPORTED

   /* It is an error to write to a read device */

   if (png_ptr->write_data_fn != NULL)

   {

      png_ptr->write_data_fn = NULL;

      png_warning(png_ptr,

          "Can't set both read_data_fn and write_data_fn in the"

          " same structure");

   }

#endif

#ifdef PNG_WRITE_FLUSH_SUPPORTED

   png_ptr->output_flush_fn = NULL;

#endif

}

#endif /* READ */