gzip_stream.h

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// Protocol Buffers - Google's data interchange format
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// Author: [email protected] (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__