src/codec/SkJpegUtility.cpp

/*
 * Copyright 2015 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "SkCodecPriv.h"
#include "SkJpegUtility.h"

/*
 * Initialize the source manager
 */
static void sk_init_source(j_decompress_ptr dinfo) {
    skjpeg_source_mgr* src = (skjpeg_source_mgr*) dinfo->src;
    src->next_input_byte = (const JOCTET*) src->fBuffer;
    src->bytes_in_buffer = 0;
}

/*
 * Fill the input buffer from the stream
 */
static boolean sk_fill_input_buffer(j_decompress_ptr dinfo) {
    skjpeg_source_mgr* src = (skjpeg_source_mgr*) dinfo->src;
    size_t bytes = src->fStream->read(src->fBuffer, skjpeg_source_mgr::kBufferSize);
    
    // libjpeg is still happy with a less than full read, as long as the result is non-zero
    if (bytes == 0) {
        return false;
    }

    src->next_input_byte = (const JOCTET*) src->fBuffer;
    src->bytes_in_buffer = bytes;
    return true;
}

/*
 * Skip a certain number of bytes in the stream
 */
static void sk_skip_input_data(j_decompress_ptr dinfo, long numBytes) {
    skjpeg_source_mgr* src = (skjpeg_source_mgr*) dinfo->src;
    size_t bytes = (size_t) numBytes;

    if (bytes > src->bytes_in_buffer) {
        size_t bytesToSkip = bytes - src->bytes_in_buffer;
        if (bytesToSkip != src->fStream->skip(bytesToSkip)) {
            SkCodecPrintf("Failure to skip.\n");
            dinfo->err->error_exit((j_common_ptr) dinfo);
            return;
        }

        src->next_input_byte = (const JOCTET*) src->fBuffer;
        src->bytes_in_buffer = 0;
    } else {
        src->next_input_byte += numBytes;
        src->bytes_in_buffer -= numBytes;
    }
}

/*
 * We do not need to do anything to terminate our stream
 */
static void sk_term_source(j_decompress_ptr dinfo)
{}

/*
 * Constructor for the source manager that we provide to libjpeg
 * We provide skia implementations of all of the stream processing functions required by libjpeg
 */
skjpeg_source_mgr::skjpeg_source_mgr(SkStream* stream)
    : fStream(stream)
{
    init_source = sk_init_source;
    fill_input_buffer = sk_fill_input_buffer;
    skip_input_data = sk_skip_input_data;
    resync_to_restart = jpeg_resync_to_restart;
    term_source = sk_term_source;
}

/*
 * Call longjmp to continue execution on an error
 */
void skjpeg_err_exit(j_common_ptr dinfo) {
    // Simply return to Skia client code
    // JpegDecoderMgr will take care of freeing memory
    skjpeg_error_mgr* error = (skjpeg_error_mgr*) dinfo->err;
    (*error->output_message) (dinfo);
    longjmp(error->fJmpBuf, 1);
}