jdatasrc.cpp

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/* +------------------------------------------------------------------------+
   |                     Mobile Robot Programming Toolkit (MRPT)            |
   |                          http://www.mrpt.org/                          |
   |                                                                        |
   | Copyright (c) 2005-2017, Individual contributors, see AUTHORS file     |
   | See: http://www.mrpt.org/Authors - All rights reserved.                |
   | Released under BSD License. See details in http://www.mrpt.org/License |
   +------------------------------------------------------------------------+ */

/* this is not a core library module, so it doesn't define JPEG_INTERNALS */
#include "jinclude.h"
#include "mrpt_jpeglib.h"
#include "jerror.h"

/* Expanded data source object for stdio input */

typedef struct
{
        struct jpeg_source_mgr pub; /* public fields */

        FILE* infile; /* source stream */
        JOCTET* buffer; /* start of buffer */
        boolean start_of_file; /* have we gotten any data yet? */
} my_source_mgr;

typedef my_source_mgr* my_src_ptr;

#define INPUT_BUF_SIZE 4096 /* choose an efficiently fread'able size */

/*
 * Initialize source --- called by jpeg_read_header
 * before any data is actually read.
 */

METHODDEF(void)
init_source(j_decompress_ptr cinfo)
{
        my_src_ptr src = (my_src_ptr)cinfo->src;

        /* We reset the empty-input-file flag for each image,
         * but we don't clear the input buffer.
         * This is correct behavior for reading a series of images from one source.
         */
        src->start_of_file = TRUE;
}

/*
 * Fill the input buffer --- called whenever buffer is emptied.
 *
 * In typical applications, this should read fresh data into the buffer
 * (ignoring the current state of next_input_byte & bytes_in_buffer),
 * reset the pointer & count to the start of the buffer, and return TRUE
 * indicating that the buffer has been reloaded.  It is not necessary to
 * fill the buffer entirely, only to obtain at least one more byte.
 *
 * There is no such thing as an EOF return.  If the end of the file has been
 * reached, the routine has a choice of ERREXIT() or inserting fake data into
 * the buffer.  In most cases, generating a warning message and inserting a
 * fake EOI marker is the best course of action --- this will allow the
 * decompressor to output however much of the image is there.  However,
 * the resulting error message is misleading if the real problem is an empty
 * input file, so we handle that case specially.
 *
 * In applications that need to be able to suspend compression due to input
 * not being available yet, a FALSE return indicates that no more data can be
 * obtained right now, but more may be forthcoming later.  In this situation,
 * the decompressor will return to its caller (with an indication of the
 * number of scanlines it has read, if any).  The application should resume
 * decompression after it has loaded more data into the input buffer.  Note
 * that there are substantial restrictions on the use of suspension --- see
 * the documentation.
 *
 * When suspending, the decompressor will back up to a convenient restart point
 * (typically the start of the current MCU). next_input_byte & bytes_in_buffer
 * indicate where the restart point will be if the current call returns FALSE.
 * Data beyond this point must be rescanned after resumption, so move it to
 * the front of the buffer rather than discarding it.
 */

METHODDEF(boolean)
fill_input_buffer(j_decompress_ptr cinfo)
{
        my_src_ptr src = (my_src_ptr)cinfo->src;
        size_t nbytes;

        nbytes = JFREAD(src->infile, src->buffer, INPUT_BUF_SIZE);

        if (nbytes <= 0)
        {
                if (src->start_of_file) /* Treat empty input file as fatal error */
                        ERREXIT(cinfo, JERR_INPUT_EMPTY);
                WARNMS(cinfo, JWRN_JPEG_EOF);
                /* Insert a fake EOI marker */
                src->buffer[0] = (JOCTET)0xFF;
                src->buffer[1] = (JOCTET)JPEG_EOI;
                nbytes = 2;
        }

        src->pub.next_input_byte = src->buffer;
        src->pub.bytes_in_buffer = nbytes;
        src->start_of_file = FALSE;

        return TRUE;
}

/*
 * Skip data --- used to skip over a potentially large amount of
 * uninteresting data (such as an APPn marker).
 *
 * Writers of suspendable-input applications must note that skip_input_data
 * is not granted the right to give a suspension return.  If the skip extends
 * beyond the data currently in the buffer, the buffer can be marked empty so
 * that the next read will cause a fill_input_buffer call that can suspend.
 * Arranging for additional bytes to be discarded before reloading the input
 * buffer is the application writer's problem.
 */

METHODDEF(void)
skip_input_data(j_decompress_ptr cinfo, long num_bytes)
{
        my_src_ptr src = (my_src_ptr)cinfo->src;

        /* Just a dumb implementation for now.  Could use fseek() except
         * it doesn't work on pipes.  Not clear that being smart is worth
         * any trouble anyway --- large skips are infrequent.
         */
        if (num_bytes > 0)
        {
                while (num_bytes > (long)src->pub.bytes_in_buffer)
                {
                        num_bytes -= (long)src->pub.bytes_in_buffer;
                        (void)fill_input_buffer(cinfo);
                        /* note we assume that fill_input_buffer will never return FALSE,
                         * so suspension need not be handled.
                         */
                }
                src->pub.next_input_byte += (size_t)num_bytes;
                src->pub.bytes_in_buffer -= (size_t)num_bytes;
        }
}

/*
 * An additional method that can be provided by data source modules is the
 * resync_to_restart method for error recovery in the presence of RST markers.
 * For the moment, this source module just uses the default resync method
 * provided by the JPEG library.  That method assumes that no backtracking
 * is possible.
 */

/*
 * Terminate source --- called by jpeg_finish_decompress
 * after all data has been read.  Often a no-op.
 *
 * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
 * application must deal with any cleanup that should happen even
 * for error exit.
 */

METHODDEF(void)
term_source(j_decompress_ptr) { /* no work necessary here */}
/*
 * Prepare for input from a stdio stream.
 * The caller must have already opened the stream, and is responsible
 * for closing it after finishing decompression.
 */

GLOBAL(void)
jpeg_stdio_src(j_decompress_ptr cinfo, FILE* infile)
{
        my_src_ptr src;

        /* The source object and input buffer are made permanent so that a series
         * of JPEG images can be read from the same file by calling jpeg_stdio_src
         * only before the first one.  (If we discarded the buffer at the end of
         * one image, we'd likely lose the start of the next one.)
         * This makes it unsafe to use this manager and a different source
         * manager serially with the same JPEG object.  Caveat programmer.
         */
        if (cinfo->src == nullptr)
        { /* first time for this JPEG object? */
                cinfo->src = (struct jpeg_source_mgr*)(*cinfo->mem->alloc_small)(
                        (j_common_ptr)cinfo, JPOOL_PERMANENT, SIZEOF(my_source_mgr));
                src = (my_src_ptr)cinfo->src;
                src->buffer = (JOCTET*)(*cinfo->mem->alloc_small)(
                        (j_common_ptr)cinfo, JPOOL_PERMANENT,
                        INPUT_BUF_SIZE * SIZEOF(JOCTET));
        }

        src = (my_src_ptr)cinfo->src;
        src->pub.init_source = init_source;
        src->pub.fill_input_buffer = fill_input_buffer;
        src->pub.skip_input_data = skip_input_data;
        src->pub.resync_to_restart =
                jpeg_resync_to_restart; /* use default method */
        src->pub.term_source = term_source;
        src->infile = infile;
        src->pub.bytes_in_buffer = 0; /* forces fill_input_buffer on first read */
        src->pub.next_input_byte = nullptr; /* until buffer loaded */
}