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Diffstat (limited to 'include/google/protobuf/io/zero_copy_stream.h')
| -rw-r--r-- | include/google/protobuf/io/zero_copy_stream.h | 260 |
1 files changed, 260 insertions, 0 deletions
diff --git a/include/google/protobuf/io/zero_copy_stream.h b/include/google/protobuf/io/zero_copy_stream.h new file mode 100644 index 0000000000..2041cbf648 --- /dev/null +++ b/include/google/protobuf/io/zero_copy_stream.h @@ -0,0 +1,260 @@ +// 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: kenton@google.com (Kenton Varda) +// Based on original Protocol Buffers design by +// Sanjay Ghemawat, Jeff Dean, and others. +// +// This file contains the ZeroCopyInputStream and ZeroCopyOutputStream +// interfaces, which represent abstract I/O streams to and from which +// protocol buffers can be read and written. For a few simple +// implementations of these interfaces, see zero_copy_stream_impl.h. +// +// These interfaces are different from classic I/O streams in that they +// try to minimize the amount of data copying that needs to be done. +// To accomplish this, responsibility for allocating buffers is moved to +// the stream object, rather than being the responsibility of the caller. +// So, the stream can return a buffer which actually points directly into +// the final data structure where the bytes are to be stored, and the caller +// can interact directly with that buffer, eliminating an intermediate copy +// operation. +// +// As an example, consider the common case in which you are reading bytes +// from an array that is already in memory (or perhaps an mmap()ed file). +// With classic I/O streams, you would do something like: +// char buffer[BUFFER_SIZE]; +// input->Read(buffer, BUFFER_SIZE); +// DoSomething(buffer, BUFFER_SIZE); +// Then, the stream basically just calls memcpy() to copy the data from +// the array into your buffer. With a ZeroCopyInputStream, you would do +// this instead: +// const void* buffer; +// int size; +// input->Next(&buffer, &size); +// DoSomething(buffer, size); +// Here, no copy is performed. The input stream returns a pointer directly +// into the backing array, and the caller ends up reading directly from it. +// +// If you want to be able to read the old-fashion way, you can create +// a CodedInputStream or CodedOutputStream wrapping these objects and use +// their ReadRaw()/WriteRaw() methods. These will, of course, add a copy +// step, but Coded*Stream will handle buffering so at least it will be +// reasonably efficient. +// +// ZeroCopyInputStream example: +// // Read in a file and print its contents to stdout. +// int fd = open("myfile", O_RDONLY); +// ZeroCopyInputStream* input = new FileInputStream(fd); +// +// const void* buffer; +// int size; +// while (input->Next(&buffer, &size)) { +// cout.write(buffer, size); +// } +// +// delete input; +// close(fd); +// +// ZeroCopyOutputStream example: +// // Copy the contents of "infile" to "outfile", using plain read() for +// // "infile" but a ZeroCopyOutputStream for "outfile". +// int infd = open("infile", O_RDONLY); +// int outfd = open("outfile", O_WRONLY); +// ZeroCopyOutputStream* output = new FileOutputStream(outfd); +// +// void* buffer; +// int size; +// while (output->Next(&buffer, &size)) { +// int bytes = read(infd, buffer, size); +// if (bytes < size) { +// // Reached EOF. +// output->BackUp(size - bytes); +// break; +// } +// } +// +// delete output; +// close(infd); +// close(outfd); + +#ifndef GOOGLE_PROTOBUF_IO_ZERO_COPY_STREAM_H__ +#define GOOGLE_PROTOBUF_IO_ZERO_COPY_STREAM_H__ + + +#include <google/protobuf/stubs/common.h> + + +// Must be included last. +#include <google/protobuf/port_def.inc> + +namespace google { +namespace protobuf { +namespace io { + +// Defined in this file. +class ZeroCopyInputStream; +class ZeroCopyOutputStream; + +// Abstract interface similar to an input stream but designed to minimize +// copying. +class PROTOBUF_EXPORT ZeroCopyInputStream { + public: + ZeroCopyInputStream() {} + virtual ~ZeroCopyInputStream() {} + + // Obtains a chunk of data from the stream. + // + // Preconditions: + // * "size" and "data" are not NULL. + // + // Postconditions: + // * If the returned value is false, there is no more data to return or + // an error occurred. All errors are permanent. + // * Otherwise, "size" points to the actual number of bytes read and "data" + // points to a pointer to a buffer containing these bytes. + // * Ownership of this buffer remains with the stream, and the buffer + // remains valid only until some other method of the stream is called + // or the stream is destroyed. + // * It is legal for the returned buffer to have zero size, as long + // as repeatedly calling Next() eventually yields a buffer with non-zero + // size. + virtual bool Next(const void** data, int* size) = 0; + + // Backs up a number of bytes, so that the next call to Next() returns + // data again that was already returned by the last call to Next(). This + // is useful when writing procedures that are only supposed to read up + // to a certain point in the input, then return. If Next() returns a + // buffer that goes beyond what you wanted to read, you can use BackUp() + // to return to the point where you intended to finish. + // + // This method can be called with `count = 0` to finalize (flush) any + // previously returned buffer. For example, a file output stream can + // flush buffers returned from a previous call to Next() upon such + // BackUp(0) invocations. ZeroCopyOutputStream callers should always + // invoke BackUp() after a final Next() call, even if there is no + // excess buffer data to be backed up to indicate a flush point. + // + // Preconditions: + // * The last method called must have been Next(). + // * count must be less than or equal to the size of the last buffer + // returned by Next(). + // + // Postconditions: + // * The last "count" bytes of the last buffer returned by Next() will be + // pushed back into the stream. Subsequent calls to Next() will return + // the same data again before producing new data. + virtual void BackUp(int count) = 0; + + // Skips a number of bytes. Returns false if the end of the stream is + // reached or some input error occurred. In the end-of-stream case, the + // stream is advanced to the end of the stream (so ByteCount() will return + // the total size of the stream). + virtual bool Skip(int count) = 0; + + // Returns the total number of bytes read since this object was created. + virtual int64_t ByteCount() const = 0; + + + private: + GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ZeroCopyInputStream); +}; + +// Abstract interface similar to an output stream but designed to minimize +// copying. +class PROTOBUF_EXPORT ZeroCopyOutputStream { + public: + ZeroCopyOutputStream() {} + virtual ~ZeroCopyOutputStream() {} + + // Obtains a buffer into which data can be written. Any data written + // into this buffer will eventually (maybe instantly, maybe later on) + // be written to the output. + // + // Preconditions: + // * "size" and "data" are not NULL. + // + // Postconditions: + // * If the returned value is false, an error occurred. All errors are + // permanent. + // * Otherwise, "size" points to the actual number of bytes in the buffer + // and "data" points to the buffer. + // * Ownership of this buffer remains with the stream, and the buffer + // remains valid only until some other method of the stream is called + // or the stream is destroyed. + // * Any data which the caller stores in this buffer will eventually be + // written to the output (unless BackUp() is called). + // * It is legal for the returned buffer to have zero size, as long + // as repeatedly calling Next() eventually yields a buffer with non-zero + // size. + virtual bool Next(void** data, int* size) = 0; + + // Backs up a number of bytes, so that the end of the last buffer returned + // by Next() is not actually written. This is needed when you finish + // writing all the data you want to write, but the last buffer was bigger + // than you needed. You don't want to write a bunch of garbage after the + // end of your data, so you use BackUp() to back up. + // + // Preconditions: + // * The last method called must have been Next(). + // * count must be less than or equal to the size of the last buffer + // returned by Next(). + // * The caller must not have written anything to the last "count" bytes + // of that buffer. + // + // Postconditions: + // * The last "count" bytes of the last buffer returned by Next() will be + // ignored. + virtual void BackUp(int count) = 0; + + // Returns the total number of bytes written since this object was created. + virtual int64_t ByteCount() const = 0; + + // Write a given chunk of data to the output. Some output streams may + // implement this in a way that avoids copying. Check AllowsAliasing() before + // calling WriteAliasedRaw(). It will GOOGLE_CHECK fail if WriteAliasedRaw() is + // called on a stream that does not allow aliasing. + // + // NOTE: It is caller's responsibility to ensure that the chunk of memory + // remains live until all of the data has been consumed from the stream. + virtual bool WriteAliasedRaw(const void* data, int size); + virtual bool AllowsAliasing() const { return false; } + + + private: + GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ZeroCopyOutputStream); +}; + +} // namespace io +} // namespace protobuf +} // namespace google + +#include <google/protobuf/port_undef.inc> + +#endif // GOOGLE_PROTOBUF_IO_ZERO_COPY_STREAM_H__ |