src/butil/zero_copy_stream_as_streambuf.h

// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

// Date: Thu Nov 22 13:57:56 CST 2012

#ifndef BUTIL_ZERO_COPY_STREAM_AS_STREAMBUF_H
#define BUTIL_ZERO_COPY_STREAM_AS_STREAMBUF_H

#include <streambuf>
#include <google/protobuf/io/zero_copy_stream.h>

namespace butil {

// Wrap a ZeroCopyOutputStream into std::streambuf. Notice that before 
// destruction or shrink(), BackUp() of the stream are not called. In another
// word, if the stream is wrapped from IOBuf, the IOBuf may be larger than 
// appended data.
class ZeroCopyStreamAsStreamBuf : public std::streambuf {
public:
    ZeroCopyStreamAsStreamBuf(google::protobuf::io::ZeroCopyOutputStream* stream)
        : _zero_copy_stream(stream) {}
    virtual ~ZeroCopyStreamAsStreamBuf();

    // BackUp() unused bytes. Automatically called in destructor.
    void shrink();
    
protected:
    int overflow(int ch) override;
    int sync() override;
    std::streampos seekoff(std::streamoff off,
                           std::ios_base::seekdir way,
                           std::ios_base::openmode which) override;

private:
    google::protobuf::io::ZeroCopyOutputStream* _zero_copy_stream;
};

}  // namespace butil

#endif  // BUTIL_ZERO_COPY_STREAM_AS_STREAMBUF_H