protobuf/io/gzip_stream.h

// Protocol Buffers - Google's data interchange format
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// Author: brianolson@google.com (Brian Olson)
//
// This file contains the definition for classes GzipInputStream and
// GzipOutputStream.
//
// GzipInputStream decompresses data from an underlying
// ZeroCopyInputStream and provides the decompressed data as a
// ZeroCopyInputStream.
//
// GzipOutputStream is an ZeroCopyOutputStream that compresses data to
// an underlying ZeroCopyOutputStream.

#ifndef GOOGLE_PROTOBUF_IO_GZIP_STREAM_H__
#define GOOGLE_PROTOBUF_IO_GZIP_STREAM_H__

#include <zlib.h>

#include <google/protobuf/stubs/common.h>
#include <google/protobuf/io/zero_copy_stream.h>

namespace google {
namespace protobuf {
namespace io {

// A ZeroCopyInputStream that reads compressed data through zlib
class LIBPROTOBUF_EXPORT GzipInputStream : public ZeroCopyInputStream {
 public:
  // Format key for constructor
  enum Format {
    // zlib will autodetect gzip header or deflate stream
    AUTO = 0,

    // GZIP streams have some extra header data for file attributes.
    GZIP = 1,

    // Simpler zlib stream format.
    ZLIB = 2,
  };

  // buffer_size and format may be -1 for default of 64kB and GZIP format
  explicit GzipInputStream(
      ZeroCopyInputStream* sub_stream,
      Format format = AUTO,
      int buffer_size = -1);
  virtual ~GzipInputStream();

  // Return last error message or NULL if no error.
  inline const char* ZlibErrorMessage() const {
    return zcontext_.msg;
  }
  inline int ZlibErrorCode() const {
    return zerror_;
  }

  // implements ZeroCopyInputStream ----------------------------------
  bool Next(const void** data, int* size);
  void BackUp(int count);
  bool Skip(int count);
  int64 ByteCount() const;

 private:
  Format format_;

  ZeroCopyInputStream* sub_stream_;

  z_stream zcontext_;
  int zerror_;

  void* output_buffer_;
  void* output_position_;
  size_t output_buffer_length_;

  int Inflate(int flush);
  void DoNextOutput(const void** data, int* size);

  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(GzipInputStream);
};


class LIBPROTOBUF_EXPORT GzipOutputStream : public ZeroCopyOutputStream {
 public:
  // Format key for constructor
  enum Format {
    // GZIP streams have some extra header data for file attributes.
    GZIP = 1,

    // Simpler zlib stream format.
    ZLIB = 2,
  };

  struct Options {
    // Defaults to GZIP.
    Format format;

    // What size buffer to use internally.  Defaults to 64kB.
    int buffer_size;

    // A number between 0 and 9, where 0 is no compression and 9 is best
    // compression.  Defaults to Z_DEFAULT_COMPRESSION (see zlib.h).
    int compression_level;

    // Defaults to Z_DEFAULT_STRATEGY.  Can also be set to Z_FILTERED,
    // Z_HUFFMAN_ONLY, or Z_RLE.  See the documentation for deflateInit2 in
    // zlib.h for definitions of these constants.
    int compression_strategy;

    Options();  // Initializes with default values.
  };

  // Create a GzipOutputStream with default options.
  explicit GzipOutputStream(ZeroCopyOutputStream* sub_stream);

  // Create a GzipOutputStream with the given options.
  GzipOutputStream(
      ZeroCopyOutputStream* sub_stream,
      const Options& options);

  virtual ~GzipOutputStream();

  // Return last error message or NULL if no error.
  inline const char* ZlibErrorMessage() const {
    return zcontext_.msg;
  }
  inline int ZlibErrorCode() const {
    return zerror_;
  }

  // Flushes data written so far to zipped data in the underlying stream.
  // It is the caller's responsibility to flush the underlying stream if
  // necessary.
  // Compression may be less efficient stopping and starting around flushes.
  // Returns true if no error.
  //
  // Please ensure that block size is > 6. Here is an excerpt from the zlib
  // doc that explains why:
  //
  // In the case of a Z_FULL_FLUSH or Z_SYNC_FLUSH, make sure that avail_out
  // is greater than six to avoid repeated flush markers due to
  // avail_out == 0 on return.
  bool Flush();

  // Writes out all data and closes the gzip stream.
  // It is the caller's responsibility to close the underlying stream if
  // necessary.
  // Returns true if no error.
  bool Close();

  // implements ZeroCopyOutputStream ---------------------------------
  bool Next(void** data, int* size);
  void BackUp(int count);
  int64 ByteCount() const;

 private:
  ZeroCopyOutputStream* sub_stream_;
  // Result from calling Next() on sub_stream_
  void* sub_data_;
  int sub_data_size_;

  z_stream zcontext_;
  int zerror_;
  void* input_buffer_;
  size_t input_buffer_length_;

  // Shared constructor code.
  void Init(ZeroCopyOutputStream* sub_stream, const Options& options);

  // Do some compression.
  // Takes zlib flush mode.
  // Returns zlib error code.
  int Deflate(int flush);

  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(GzipOutputStream);
};

}  // namespace io
}  // namespace protobuf

}  // namespace google
#endif  // GOOGLE_PROTOBUF_IO_GZIP_STREAM_H__