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+// 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 <string>
+#include <google/protobuf/stubs/common.h>
+
+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 LIBPROTOBUF_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.
+ //
+ // 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 ByteCount() const = 0;
+
+
+ private:
+ GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ZeroCopyInputStream);
+};
+
+// Abstract interface similar to an output stream but designed to minimize
+// copying.
+class LIBPROTOBUF_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 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
+#endif // GOOGLE_PROTOBUF_IO_ZERO_COPY_STREAM_H__