zero_copy_stream_impl.h

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// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc. All rights reserved.
// https://developers.google.com/protocol-buffers/
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// Author: [email protected] (Kenton Varda)
// Based on original Protocol Buffers design by
// Sanjay Ghemawat, Jeff Dean, and others.
//
// This file contains common implementations of the interfaces defined in
// zero_copy_stream.h which are only included in the full (non-lite)
// protobuf library. These implementations include Unix file descriptors
// and C++ iostreams. See also: zero_copy_stream_impl_lite.h

#ifndef GOOGLE_PROTOBUF_IO_ZERO_COPY_STREAM_IMPL_H__
#define GOOGLE_PROTOBUF_IO_ZERO_COPY_STREAM_IMPL_H__

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


namespace google {
namespace protobuf {
namespace io {


// ===================================================================

// A ZeroCopyInputStream which reads from a file descriptor.
//
// FileInputStream is preferred over using an ifstream with IstreamInputStream.
// The latter will introduce an extra layer of buffering, harming performance.
// Also, it's conceivable that FileInputStream could someday be enhanced
// to use zero-copy file descriptors on OSs which support them.
class LIBPROTOBUF_EXPORT FileInputStream : public ZeroCopyInputStream {
 public:
 // Creates a stream that reads from the given Unix file descriptor.
 // If a block_size is given, it specifies the number of bytes that
 // should be read and returned with each call to Next(). Otherwise,
 // a reasonable default is used.
 explicit FileInputStream(int file_descriptor, int block_size = -1);
 ~FileInputStream();

 // Flushes any buffers and closes the underlying file. Returns false if
 // an error occurs during the process; use GetErrno() to examine the error.
 // Even if an error occurs, the file descriptor is closed when this returns.
 bool Close();

 // By default, the file descriptor is not closed when the stream is
 // destroyed. Call SetCloseOnDelete(true) to change that. WARNING:
 // This leaves no way for the caller to detect if close() fails. If
 // detecting close() errors is important to you, you should arrange
 // to close the descriptor yourself.
 void SetCloseOnDelete(bool value) { copying_input_.SetCloseOnDelete(value); }

 // If an I/O error has occurred on this file descriptor, this is the
 // errno from that error. Otherwise, this is zero. Once an error
 // occurs, the stream is broken and all subsequent operations will
 // fail.
 int GetErrno() { return copying_input_.GetErrno(); }

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

 private:
 class LIBPROTOBUF_EXPORT CopyingFileInputStream : public CopyingInputStream {
 public:
 CopyingFileInputStream(int file_descriptor);
 ~CopyingFileInputStream();

 bool Close();
 void SetCloseOnDelete(bool value) { close_on_delete_ = value; }
 int GetErrno() { return errno_; }

 // implements CopyingInputStream ---------------------------------
 int Read(void* buffer, int size);
 int Skip(int count);

 private:
 // The file descriptor.
 const int file_;
 bool close_on_delete_;
 bool is_closed_;

 // The errno of the I/O error, if one has occurred. Otherwise, zero.
 int errno_;

 // Did we try to seek once and fail? If so, we assume this file descriptor
 // doesn't support seeking and won't try again.
 bool previous_seek_failed_;

 GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(CopyingFileInputStream);
 };

 CopyingFileInputStream copying_input_;
 CopyingInputStreamAdaptor impl_;

 GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(FileInputStream);
};

// ===================================================================

// A ZeroCopyOutputStream which writes to a file descriptor.
//
// FileOutputStream is preferred over using an ofstream with
// OstreamOutputStream. The latter will introduce an extra layer of buffering,
// harming performance. Also, it's conceivable that FileOutputStream could
// someday be enhanced to use zero-copy file descriptors on OSs which
// support them.
class LIBPROTOBUF_EXPORT FileOutputStream : public ZeroCopyOutputStream {
 public:
 // Creates a stream that writes to the given Unix file descriptor.
 // If a block_size is given, it specifies the size of the buffers
 // that should be returned by Next(). Otherwise, a reasonable default
 // is used.
 explicit FileOutputStream(int file_descriptor, int block_size = -1);
 ~FileOutputStream();

 // Flushes any buffers and closes the underlying file. Returns false if
 // an error occurs during the process; use GetErrno() to examine the error.
 // Even if an error occurs, the file descriptor is closed when this returns.
 bool Close();

 // Flushes FileOutputStream's buffers but does not close the
 // underlying file. No special measures are taken to ensure that
 // underlying operating system file object is synchronized to disk.
 bool Flush();

 // By default, the file descriptor is not closed when the stream is
 // destroyed. Call SetCloseOnDelete(true) to change that. WARNING:
 // This leaves no way for the caller to detect if close() fails. If
 // detecting close() errors is important to you, you should arrange
 // to close the descriptor yourself.
 void SetCloseOnDelete(bool value) { copying_output_.SetCloseOnDelete(value); }

 // If an I/O error has occurred on this file descriptor, this is the
 // errno from that error. Otherwise, this is zero. Once an error
 // occurs, the stream is broken and all subsequent operations will
 // fail.
 int GetErrno() { return copying_output_.GetErrno(); }

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

 private:
 class LIBPROTOBUF_EXPORT CopyingFileOutputStream : public CopyingOutputStream {
 public:
 CopyingFileOutputStream(int file_descriptor);
 ~CopyingFileOutputStream();

 bool Close();
 void SetCloseOnDelete(bool value) { close_on_delete_ = value; }
 int GetErrno() { return errno_; }

 // implements CopyingOutputStream --------------------------------
 bool Write(const void* buffer, int size);

 private:
 // The file descriptor.
 const int file_;
 bool close_on_delete_;
 bool is_closed_;

 // The errno of the I/O error, if one has occurred. Otherwise, zero.
 int errno_;

 GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(CopyingFileOutputStream);
 };

 CopyingFileOutputStream copying_output_;
 CopyingOutputStreamAdaptor impl_;

 GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(FileOutputStream);
};

// ===================================================================

// A ZeroCopyInputStream which reads from a C++ istream.
//
// Note that for reading files (or anything represented by a file descriptor),
// FileInputStream is more efficient.
class LIBPROTOBUF_EXPORT IstreamInputStream : public ZeroCopyInputStream {
 public:
 // Creates a stream that reads from the given C++ istream.
 // If a block_size is given, it specifies the number of bytes that
 // should be read and returned with each call to Next(). Otherwise,
 // a reasonable default is used.
 explicit IstreamInputStream(istream* stream, int block_size = -1);
 ~IstreamInputStream();

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

 private:
 class LIBPROTOBUF_EXPORT CopyingIstreamInputStream : public CopyingInputStream {
 public:
 CopyingIstreamInputStream(istream* input);
 ~CopyingIstreamInputStream();

 // implements CopyingInputStream ---------------------------------
 int Read(void* buffer, int size);
 // (We use the default implementation of Skip().)

 private:
 // The stream.
 istream* input_;

 GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(CopyingIstreamInputStream);
 };

 CopyingIstreamInputStream copying_input_;
 CopyingInputStreamAdaptor impl_;

 GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(IstreamInputStream);
};

// ===================================================================

// A ZeroCopyOutputStream which writes to a C++ ostream.
//
// Note that for writing files (or anything represented by a file descriptor),
// FileOutputStream is more efficient.
class LIBPROTOBUF_EXPORT OstreamOutputStream : public ZeroCopyOutputStream {
 public:
 // Creates a stream that writes to the given C++ ostream.
 // If a block_size is given, it specifies the size of the buffers
 // that should be returned by Next(). Otherwise, a reasonable default
 // is used.
 explicit OstreamOutputStream(ostream* stream, int block_size = -1);
 ~OstreamOutputStream();

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

 private:
 class LIBPROTOBUF_EXPORT CopyingOstreamOutputStream : public CopyingOutputStream {
 public:
 CopyingOstreamOutputStream(ostream* output);
 ~CopyingOstreamOutputStream();

 // implements CopyingOutputStream --------------------------------
 bool Write(const void* buffer, int size);

 private:
 // The stream.
 ostream* output_;

 GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(CopyingOstreamOutputStream);
 };

 CopyingOstreamOutputStream copying_output_;
 CopyingOutputStreamAdaptor impl_;

 GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(OstreamOutputStream);
};

// ===================================================================

// A ZeroCopyInputStream which reads from several other streams in sequence.
// ConcatenatingInputStream is unable to distinguish between end-of-stream
// and read errors in the underlying streams, so it assumes any errors mean
// end-of-stream. So, if the underlying streams fail for any other reason,
// ConcatenatingInputStream may do odd things. It is suggested that you do
// not use ConcatenatingInputStream on streams that might produce read errors
// other than end-of-stream.
class LIBPROTOBUF_EXPORT ConcatenatingInputStream : public ZeroCopyInputStream {
 public:
 // All streams passed in as well as the array itself must remain valid
 // until the ConcatenatingInputStream is destroyed.
 ConcatenatingInputStream(ZeroCopyInputStream* const streams[], int count);
 ~ConcatenatingInputStream();

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


 private:
 // As streams are retired, streams_ is incremented and count_ is
 // decremented.
 ZeroCopyInputStream* const* streams_;
 int stream_count_;
 int64 bytes_retired_; // Bytes read from previous streams.

 GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ConcatenatingInputStream);
};

// ===================================================================

// A ZeroCopyInputStream which wraps some other stream and limits it to
// a particular byte count.
class LIBPROTOBUF_EXPORT LimitingInputStream : public ZeroCopyInputStream {
 public:
 LimitingInputStream(ZeroCopyInputStream* input, int64 limit);
 ~LimitingInputStream();

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


 private:
 ZeroCopyInputStream* input_;
 int64 limit_; // Decreases as we go, becomes negative if we overshoot.
 int64 prior_bytes_read_; // Bytes read on underlying stream at construction

 GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(LimitingInputStream);
};

// ===================================================================

} // namespace io
} // namespace protobuf

} // namespace google
#endif // GOOGLE_PROTOBUF_IO_ZERO_COPY_STREAM_IMPL_H__