text: /*
   * 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 "src/codec/SkJpegUtility.h"
  
  #include "src/codec/SkCodecPriv.h"
  
  /*
   * 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);
    if (error->fJmpBufStack.empty()) {
      SK_ABORT("JPEG error with no jmp_buf set.");
    }
    longjmp(*error->fJmpBufStack.back(), 1);
  }
  
  // Functions for buffered sources //
  
  /*
   * Initialize the buffered source manager
   */
  static void sk_init_buffered_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_buffered_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) {
      // Let libjpeg know that the buffer needs to be refilled
      src->next_input_byte = nullptr;
      src->bytes_in_buffer = 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_buffered_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) {
    // The current implementation of SkJpegCodec does not call
    // jpeg_finish_decompress(), so this function is never called.
    // If we want to modify this function to do something, we also
    // need to modify SkJpegCodec to call jpeg_finish_decompress().
  }
  
  // Functions for memory backed sources //
  
  /*
   * Initialize the mem backed source manager
   */
  static void sk_init_mem_source(j_decompress_ptr dinfo) {
    /* no work necessary here, all things are done in constructor */
  }
  
  static void sk_skip_mem_input_data(j_decompress_ptr cinfo, long num_bytes) {
    jpeg_source_mgr* src = cinfo->src;
    size_t bytes = static_cast<size_t>(num_bytes);
    if (bytes > src->bytes_in_buffer) {
      src->next_input_byte = nullptr;
      src->bytes_in_buffer = 0;
    } else {
      src->next_input_byte += bytes;
      src->bytes_in_buffer -= bytes;
    }
  }
  
  static boolean sk_fill_mem_input_buffer(j_decompress_ptr cinfo) {
    /* The whole JPEG data is expected to reside in the supplied memory,
     * buffer, so any request for more data beyond the given buffer size
     * is treated as an error.
     */
    return false;
  }
  
  /*
   * 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) {
    if (stream->hasLength() && stream->getMemoryBase()) {
      init_source = sk_init_mem_source;
      fill_input_buffer = sk_fill_mem_input_buffer;
      skip_input_data = sk_skip_mem_input_data;
      resync_to_restart = jpeg_resync_to_restart;
      term_source = sk_term_source;
      bytes_in_buffer = static_cast<size_t>(stream->getLength());
      next_input_byte = static_cast<const JOCTET*>(stream->getMemoryBase());
    } else {
      init_source = sk_init_buffered_source;
      fill_input_buffer = sk_fill_buffered_input_buffer;
      skip_input_data = sk_skip_buffered_input_data;
      resync_to_restart = jpeg_resync_to_restart;
      term_source = sk_term_source;
    }
  }
  