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120 lines
3.8 KiB
C
120 lines
3.8 KiB
C
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/* pngrio.c - functions for data input
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*
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* Copyright (c) 2018 Cosmin Truta
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* Copyright (c) 1998-2002,2004,2006-2016,2018 Glenn Randers-Pehrson
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* Copyright (c) 1996-1997 Andreas Dilger
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* 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
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* special handling are expected to write a function that has the same
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* arguments as this and performs a similar function, but that possibly
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* 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
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* libpng use it at run time with png_set_read_fn(...).
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*/
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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
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* with very small lengths, so you should implement some kind of simple
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* 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
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png_error(png_ptr, "Call to NULL read function");
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}
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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
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* read_data function and use it at run time with png_set_read_fn(), rather
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* than changing the library.
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*/
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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)
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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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*/
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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)
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png_error(png_ptr, "Read Error");
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}
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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.
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*
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* 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
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* 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
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* arguments a pointer to a png_struct, a pointer to
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* a location where input data can be stored, and a 32-bit
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* unsigned int that is the number of bytes to be read.
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* To exit and output any fatal error messages the new write
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* function should call png_error(png_ptr, "Error msg").
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* May be NULL, in which case libpng's default function will
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* be used.
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*/
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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)
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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
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png_ptr->read_data_fn = read_data_fn;
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#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)
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{
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png_ptr->write_data_fn = NULL;
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png_warning(png_ptr,
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"Can't set both read_data_fn and write_data_fn in the"
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" 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 */
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