zero_copy_stream_impl_lite.h

Go to the documentation of this file.

// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc. All rights reserved.
// https://developers.google.com/protocol-buffers/
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

// 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 included in the "lite" protobuf library.
// These implementations cover I/O on raw arrays and strings, as well as
// adaptors which make it easy to implement streams based on traditional
// streams. Of course, many users will probably want to write their own
// implementations of these interfaces specific to the particular I/O
// abstractions they prefer to use, but these should cover the most common
// cases.

#ifndef GOOGLE_PROTOBUF_IO_ZERO_COPY_STREAM_IMPL_LITE_H__
#define GOOGLE_PROTOBUF_IO_ZERO_COPY_STREAM_IMPL_LITE_H__

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


namespace google {
namespace protobuf {
namespace io {

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

// A ZeroCopyInputStream backed by an in-memory array of bytes.
class LIBPROTOBUF_EXPORT ArrayInputStream : public ZeroCopyInputStream {
 public:
 // Create an InputStream that returns the bytes pointed to by "data".
 // "data" remains the property of the caller but must remain valid until
 // the stream is destroyed. If a block_size is given, calls to Next()
 // will return data blocks no larger than the given size. Otherwise, the
 // first call to Next() returns the entire array. block_size is mainly
 // useful for testing; in production you would probably never want to set
 // it.
 ArrayInputStream(const void* data, int size, int block_size = -1);
 ~ArrayInputStream();

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


 private:
 const uint8* const data_; // The byte array.
 const int size_; // Total size of the array.
 const int block_size_; // How many bytes to return at a time.

 int position_;
 int last_returned_size_; // How many bytes we returned last time Next()
 // was called (used for error checking only).

 GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ArrayInputStream);
};

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

// A ZeroCopyOutputStream backed by an in-memory array of bytes.
class LIBPROTOBUF_EXPORT ArrayOutputStream : public ZeroCopyOutputStream {
 public:
 // Create an OutputStream that writes to the bytes pointed to by "data".
 // "data" remains the property of the caller but must remain valid until
 // the stream is destroyed. If a block_size is given, calls to Next()
 // will return data blocks no larger than the given size. Otherwise, the
 // first call to Next() returns the entire array. block_size is mainly
 // useful for testing; in production you would probably never want to set
 // it.
 ArrayOutputStream(void* data, int size, int block_size = -1);
 ~ArrayOutputStream();

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

 private:
 uint8* const data_; // The byte array.
 const int size_; // Total size of the array.
 const int block_size_; // How many bytes to return at a time.

 int position_;
 int last_returned_size_; // How many bytes we returned last time Next()
 // was called (used for error checking only).

 GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ArrayOutputStream);
};

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

// A ZeroCopyOutputStream which appends bytes to a string.
class LIBPROTOBUF_EXPORT StringOutputStream : public ZeroCopyOutputStream {
 public:
 // Create a StringOutputStream which appends bytes to the given string.
 // The string remains property of the caller, but it MUST NOT be accessed
 // in any way until the stream is destroyed.
 //
 // Hint: If you call target->reserve(n) before creating the stream,
 // the first call to Next() will return at least n bytes of buffer
 // space.
 explicit StringOutputStream(string* target);
 ~StringOutputStream();

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

 private:
 static const int kMinimumSize = 16;

 string* target_;

 GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(StringOutputStream);
};

// Note: There is no StringInputStream. Instead, just create an
// ArrayInputStream as follows:
// ArrayInputStream input(str.data(), str.size());

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

// A generic traditional input stream interface.
//
// Lots of traditional input streams (e.g. file descriptors, C stdio
// streams, and C++ iostreams) expose an interface where every read
// involves copying bytes into a buffer. If you want to take such an
// interface and make a ZeroCopyInputStream based on it, simply implement
// CopyingInputStream and then use CopyingInputStreamAdaptor.
//
// CopyingInputStream implementations should avoid buffering if possible.
// CopyingInputStreamAdaptor does its own buffering and will read data
// in large blocks.
class LIBPROTOBUF_EXPORT CopyingInputStream {
 public:
 virtual ~CopyingInputStream();

 // Reads up to "size" bytes into the given buffer. Returns the number of
 // bytes read. Read() waits until at least one byte is available, or
 // returns zero if no bytes will ever become available (EOF), or -1 if a
 // permanent read error occurred.
 virtual int Read(void* buffer, int size) = 0;

 // Skips the next "count" bytes of input. Returns the number of bytes
 // actually skipped. This will always be exactly equal to "count" unless
 // EOF was reached or a permanent read error occurred.
 //
 // The default implementation just repeatedly calls Read() into a scratch
 // buffer.
 virtual int Skip(int count);
};

// A ZeroCopyInputStream which reads from a CopyingInputStream. This is
// useful for implementing ZeroCopyInputStreams that read from traditional
// streams. Note that this class is not really zero-copy.
//
// If you want to read from file descriptors or C++ istreams, this is
// already implemented for you: use FileInputStream or IstreamInputStream
// respectively.
class LIBPROTOBUF_EXPORT CopyingInputStreamAdaptor : public ZeroCopyInputStream {
 public:
 // Creates a stream that reads from the given CopyingInputStream.
 // 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. The caller retains ownership of
 // copying_stream unless SetOwnsCopyingStream(true) is called.
 explicit CopyingInputStreamAdaptor(CopyingInputStream* copying_stream,
 int block_size = -1);
 ~CopyingInputStreamAdaptor();

 // Call SetOwnsCopyingStream(true) to tell the CopyingInputStreamAdaptor to
 // delete the underlying CopyingInputStream when it is destroyed.
 void SetOwnsCopyingStream(bool value) { owns_copying_stream_ = value; }

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

 private:
 // Insures that buffer_ is not NULL.
 void AllocateBufferIfNeeded();
 // Frees the buffer and resets buffer_used_.
 void FreeBuffer();

 // The underlying copying stream.
 CopyingInputStream* copying_stream_;
 bool owns_copying_stream_;

 // True if we have seen a permenant error from the underlying stream.
 bool failed_;

 // The current position of copying_stream_, relative to the point where
 // we started reading.
 int64 position_;

 // Data is read into this buffer. It may be NULL if no buffer is currently
 // in use. Otherwise, it points to an array of size buffer_size_.
 scoped_array<uint8> buffer_;
 const int buffer_size_;

 // Number of valid bytes currently in the buffer (i.e. the size last
 // returned by Next()). 0 <= buffer_used_ <= buffer_size_.
 int buffer_used_;

 // Number of bytes in the buffer which were backed up over by a call to
 // BackUp(). These need to be returned again.
 // 0 <= backup_bytes_ <= buffer_used_
 int backup_bytes_;

 GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(CopyingInputStreamAdaptor);
};

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

// A generic traditional output stream interface.
//
// Lots of traditional output streams (e.g. file descriptors, C stdio
// streams, and C++ iostreams) expose an interface where every write
// involves copying bytes from a buffer. If you want to take such an
// interface and make a ZeroCopyOutputStream based on it, simply implement
// CopyingOutputStream and then use CopyingOutputStreamAdaptor.
//
// CopyingOutputStream implementations should avoid buffering if possible.
// CopyingOutputStreamAdaptor does its own buffering and will write data
// in large blocks.
class LIBPROTOBUF_EXPORT CopyingOutputStream {
 public:
 virtual ~CopyingOutputStream();

 // Writes "size" bytes from the given buffer to the output. Returns true
 // if successful, false on a write error.
 virtual bool Write(const void* buffer, int size) = 0;
};

// A ZeroCopyOutputStream which writes to a CopyingOutputStream. This is
// useful for implementing ZeroCopyOutputStreams that write to traditional
// streams. Note that this class is not really zero-copy.
//
// If you want to write to file descriptors or C++ ostreams, this is
// already implemented for you: use FileOutputStream or OstreamOutputStream
// respectively.
class LIBPROTOBUF_EXPORT CopyingOutputStreamAdaptor : 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 CopyingOutputStreamAdaptor(CopyingOutputStream* copying_stream,
 int block_size = -1);
 ~CopyingOutputStreamAdaptor();

 // Writes all pending data to the underlying stream. Returns false if a
 // write error occurred on the underlying stream. (The underlying
 // stream itself is not necessarily flushed.)
 bool Flush();

 // Call SetOwnsCopyingStream(true) to tell the CopyingOutputStreamAdaptor to
 // delete the underlying CopyingOutputStream when it is destroyed.
 void SetOwnsCopyingStream(bool value) { owns_copying_stream_ = value; }

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

 private:
 // Write the current buffer, if it is present.
 bool WriteBuffer();
 // Insures that buffer_ is not NULL.
 void AllocateBufferIfNeeded();
 // Frees the buffer.
 void FreeBuffer();

 // The underlying copying stream.
 CopyingOutputStream* copying_stream_;
 bool owns_copying_stream_;

 // True if we have seen a permenant error from the underlying stream.
 bool failed_;

 // The current position of copying_stream_, relative to the point where
 // we started writing.
 int64 position_;

 // Data is written from this buffer. It may be NULL if no buffer is
 // currently in use. Otherwise, it points to an array of size buffer_size_.
 scoped_array<uint8> buffer_;
 const int buffer_size_;

 // Number of valid bytes currently in the buffer (i.e. the size last
 // returned by Next()). When BackUp() is called, we just reduce this.
 // 0 <= buffer_used_ <= buffer_size_.
 int buffer_used_;

 GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(CopyingOutputStreamAdaptor);
};

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

// Return a pointer to mutable characters underlying the given string. The
// return value is valid until the next time the string is resized. We
// trust the caller to treat the return value as an array of length s->size().
inline char* mutable_string_data(string* s) {
#ifdef LANG_CXX11
 // This should be simpler & faster than string_as_array() because the latter
 // is guaranteed to return NULL when *s is empty, so it has to check for that.
 return &(*s)[0];
#else
 return string_as_array(s);
#endif
}

} // namespace io
} // namespace protobuf

} // namespace google
#endif // GOOGLE_PROTOBUF_IO_ZERO_COPY_STREAM_IMPL_LITE_H__