146 lines
4.6 KiB
C
146 lines
4.6 KiB
C
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/* pngrio.c - functions for data input
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*
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* libpng 1.00
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* For conditions of distribution and use, see copyright notice in png.h
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* Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
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* Copyright (c) 1996, 1997 Andreas Dilger
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* Copyright (c) 1998, Glenn Randers-Pehrson
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* March 7, 1998
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*
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* This file provides a location for all input. Users which need
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* special handling are expected to write a function which has the same
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* arguments as this, and perform a similar function, but possibly has
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* 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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#define PNG_INTERNAL
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#include "png.h"
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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 then 64K on a 16 bit machine. */
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void
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png_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
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{
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png_debug1(4,"reading %d bytes\n", 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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#if !defined(PNG_NO_STDIO)
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/* This is the function which 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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#ifndef USE_FAR_KEYWORD
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static void
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png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
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{
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png_size_t check;
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/* fread() returns 0 on error, so it is OK to store this in a png_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 = (png_size_t)fread(data, (png_size_t)1, length,
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(FILE *)png_ptr->io_ptr);
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if (check != length)
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{
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png_error(png_ptr, "Read Error");
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}
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}
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#else
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/* this is the model-independent version. Since the standard I/O library
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can't handle far buffers in the medium and small models, we have to copy
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the data.
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*/
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#define NEAR_BUF_SIZE 1024
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#define MIN(a,b) (a <= b ? a : b)
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static void
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png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
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{
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int check;
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png_byte *n_data;
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FILE *io_ptr;
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/* Check if data really is near. If so, use usual code. */
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n_data = (png_byte *)CVT_PTR_NOCHECK(data);
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io_ptr = (FILE *)CVT_PTR(png_ptr->io_ptr);
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if ((png_bytep)n_data == data)
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{
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check = fread(n_data, 1, length, io_ptr);
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}
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else
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{
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png_byte buf[NEAR_BUF_SIZE];
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png_size_t read, remaining, err;
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check = 0;
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remaining = length;
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do
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{
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read = MIN(NEAR_BUF_SIZE, remaining);
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err = fread(buf, (png_size_t)1, read, io_ptr);
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png_memcpy(data, buf, read); /* copy far buffer to near buffer */
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if(err != read)
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break;
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else
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check += err;
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data += read;
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remaining -= read;
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}
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while (remaining != 0);
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}
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if ((png_uint_32)check != (png_uint_32)length)
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{
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png_error(png_ptr, "read Error");
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}
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}
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#endif
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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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This function takes as its arguments:
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png_ptr - pointer to a png input data structure
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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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read_data_fn - pointer to a new input function which takes as it's
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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 which 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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void
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png_set_read_fn(png_structp png_ptr, png_voidp io_ptr,
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png_rw_ptr read_data_fn)
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{
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png_ptr->io_ptr = io_ptr;
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#if !defined(PNG_NO_STDIO)
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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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/* It is an error to write to a read device */
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png_ptr->write_data_fn = NULL;
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#if defined(PNG_WRITE_FLUSH_SUPPORTED)
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png_ptr->output_flush_fn = NULL;
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#endif /* PNG_WRITE_FLUSH_SUPPORTED */
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}
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