bspatch.cc - platform/external/bsdiff - Gitiles

 /*-
  * Copyright 2003-2005 Colin Percival
  * All rights reserved
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted providing that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. 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.
  *
  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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.
  */

 #if 0
 __FBSDID("$FreeBSD: src/usr.bin/bsdiff/bspatch/bspatch.c,v 1.1 2005/08/06 01:59:06 cperciva Exp $");
 #endif

 #include "bsdiff/bspatch.h"

 #include <errno.h>
 #include <fcntl.h>
 #include <inttypes.h>
 #include <stdio.h>
 #include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <unistd.h>

 #include <algorithm>
 #include <memory>
 #include <vector>

 #include "bsdiff/buffer_file.h"
 #include "bsdiff/control_entry.h"
 #include "bsdiff/extents.h"
 #include "bsdiff/extents_file.h"
 #include "bsdiff/file.h"
 #include "bsdiff/file_interface.h"
 #include "bsdiff/logging.h"
 #include "bsdiff/memory_file.h"
 #include "bsdiff/patch_reader.h"
 #include "bsdiff/sink_file.h"
 #include "bsdiff/utils.h"

 namespace {
 // Read the data in |stream| and write |size| decompressed data to |file|;
 // using the buffer in |buf| with size |buf_size|.
 // Returns 0 on success, 1 on I/O error and 2 on data error.
 int ReadStreamAndWriteAll(
     const std::unique_ptr<bsdiff::FileInterface>& file,
     size_t size,
     uint8_t* buf,
     size_t buf_size,
     const std::function<bool(uint8_t*, size_t)>& read_func) {
   while (size > 0) {
     size_t bytes_to_output = std::min(size, buf_size);
     if (!read_func(buf, bytes_to_output)) {
       LOG(ERROR) << "Failed to read stream.";
       return 2;
     }

     if (!WriteAll(file, buf, bytes_to_output)) {
       PLOG(ERROR) << "WriteAll() failed.";
       return 1;
     }
     size -= bytes_to_output;
   }
   return 0;
 }

 }  // namespace

 namespace bsdiff {

 bool ReadAll(const std::unique_ptr<FileInterface>& file,
              uint8_t* data,
              size_t size) {
   size_t offset = 0, read;
   while (offset < size) {
     if (!file->Read(data + offset, size - offset, &read) || read == 0)
       return false;
     offset += read;
   }
   return true;
 }

 bool WriteAll(const std::unique_ptr<FileInterface>& file,
               const uint8_t* data,
               size_t size) {
   size_t offset = 0, written;
   while (offset < size) {
     if (!file->Write(data + offset, size - offset, &written) || written == 0)
       return false;
     offset += written;
   }
   return true;
 }

 bool IsOverlapping(const char* old_filename,
                    const char* new_filename,
                    const std::vector<ex_t>& old_extents,
                    const std::vector<ex_t>& new_extents) {
   struct stat old_stat, new_stat;
   if (stat(new_filename, &new_stat) == -1) {
     if (errno == ENOENT)
       return false;
     PLOG(ERROR) << "Error stat the new file: " << new_filename;
     return true;
   }
   if (stat(old_filename, &old_stat) == -1) {
     PLOG(ERROR) << "Error stat the old file: " << old_filename;
     return true;
   }

   if (old_stat.st_dev != new_stat.st_dev || old_stat.st_ino != new_stat.st_ino)
     return false;

   if (old_extents.empty() && new_extents.empty())
     return true;

   for (ex_t old_ex : old_extents)
     for (ex_t new_ex : new_extents)
       if (static_cast<uint64_t>(old_ex.off) < new_ex.off + new_ex.len &&
           static_cast<uint64_t>(new_ex.off) < old_ex.off + old_ex.len)
         return true;

   return false;
 }

 // Patch |old_filename| with |patch_filename| and save it to |new_filename|.
 // |old_extents| and |new_extents| are comma-separated lists of "offset:length"
 // extents of |old_filename| and |new_filename|.
 // Returns 0 on success, 1 on I/O error and 2 on data error.
 int bspatch(const char* old_filename,
             const char* new_filename,
             const char* patch_filename,
             const char* old_extents,
             const char* new_extents) {
   std::unique_ptr<FileInterface> patch_file =
       File::FOpen(patch_filename, O_RDONLY);
   if (!patch_file) {
     PLOG(ERROR) << "Error opening the patch file: " << patch_filename;
     return 1;
   }
   uint64_t patch_size;
   patch_file->GetSize(&patch_size);
   std::vector<uint8_t> patch(patch_size);
   if (!ReadAll(patch_file, patch.data(), patch_size)) {
     PLOG(ERROR) << "Error reading the patch file: " << patch_filename;
     return 1;
   }
   patch_file.reset();

   return bspatch(old_filename, new_filename, patch.data(), patch_size,
                  old_extents, new_extents);
 }

 // Patch |old_filename| with |patch_data| and save it to |new_filename|.
 // |old_extents| and |new_extents| are comma-separated lists of "offset:length"
 // extents of |old_filename| and |new_filename|.
 // Returns 0 on success, 1 on I/O error and 2 on data error.
 int bspatch(const char* old_filename,
             const char* new_filename,
             const uint8_t* patch_data,
             size_t patch_size,
             const char* old_extents,
             const char* new_extents) {
   int using_extents = (old_extents != NULL || new_extents != NULL);

   // Open input file for reading.
   std::unique_ptr<FileInterface> old_file = File::FOpen(old_filename, O_RDONLY);
   if (!old_file) {
     PLOG(ERROR) << "Error opening the old file: " << old_filename;
     return 1;
   }

   std::vector<ex_t> parsed_old_extents;
   if (using_extents) {
     if (!ParseExtentStr(old_extents, &parsed_old_extents)) {
       LOG(ERROR) << "Error parsing the old extents.";
       return 2;
     }
     old_file.reset(new ExtentsFile(std::move(old_file), parsed_old_extents));
   }

   // Open output file for writing.
   std::unique_ptr<FileInterface> new_file =
       File::FOpen(new_filename, O_CREAT | O_WRONLY);
   if (!new_file) {
     PLOG(ERROR) << "Error opening the new file: " << new_filename;
     return 1;
   }

   std::vector<ex_t> parsed_new_extents;
   if (using_extents) {
     if (!ParseExtentStr(new_extents, &parsed_new_extents)) {
       LOG(ERROR) << "Error parsing the new extents.";
       return 2;
     }
     new_file.reset(new ExtentsFile(std::move(new_file), parsed_new_extents));
   }

   if (IsOverlapping(old_filename, new_filename, parsed_old_extents,
                     parsed_new_extents)) {
     // New and old file is overlapping, we can not stream output to new file,
     // cache it in a buffer and write to the file at the end.
     uint64_t newsize = ParseInt64(patch_data + 24);
     new_file.reset(new BufferFile(std::move(new_file), newsize));
   }

   return bspatch(old_file, new_file, patch_data, patch_size);
 }

 // Patch |old_data| with |patch_data| and save it by calling sink function.
 // Returns 0 on success, 1 on I/O error and 2 on data error.
 int bspatch(const uint8_t* old_data,
             size_t old_size,
             const uint8_t* patch_data,
             size_t patch_size,
             const sink_func& sink) {
   std::unique_ptr<FileInterface> old_file(new MemoryFile(old_data, old_size));
   std::unique_ptr<FileInterface> new_file(new SinkFile(sink));

   return bspatch(old_file, new_file, patch_data, patch_size);
 }

 // Patch |old_file| with |patch_data| and save it to |new_file|.
 // Returns 0 on success, 1 on I/O error and 2 on data error.
 int bspatch(const std::unique_ptr<FileInterface>& old_file,
             const std::unique_ptr<FileInterface>& new_file,
             const uint8_t* patch_data,
             size_t patch_size) {
   BsdiffPatchReader patch_reader;
   if (!patch_reader.Init(patch_data, patch_size)) {
     LOG(ERROR) << "Failed to initialize patch reader.";
     return 2;
   }

   uint64_t old_file_size;
   if (!old_file->GetSize(&old_file_size)) {
     LOG(ERROR) << "Cannot obtain the size of old file.";
     return 1;
   }

   // The oldpos can be negative, but the new pos is only incremented linearly.
   int64_t oldpos = 0;
   uint64_t newpos = 0;
   std::vector<uint8_t> old_buf(1024 * 1024);
   std::vector<uint8_t> new_buf(1024 * 1024);
   uint64_t old_file_pos = 0;
   while (newpos < patch_reader.new_file_size()) {
     ControlEntry control_entry(0, 0, 0);
     if (!patch_reader.ParseControlEntry(&control_entry)) {
       LOG(ERROR) << "Failed to read control stream.";
       return 2;
     }

     // Sanity-check.
     if (newpos + control_entry.diff_size > patch_reader.new_file_size()) {
       LOG(ERROR) << "Corrupt patch.";
       return 2;
     }

     int ret = 0;
     // Add old data to diff string. It is enough to fseek once, at
     // the beginning of the sequence, to avoid unnecessary overhead.
     int64_t seek_offset = oldpos;
     if (seek_offset < 0) {
       // Write diff block directly to new file without adding old data,
       // because we will skip part where |oldpos| < 0.
       ret = ReadStreamAndWriteAll(
           new_file, oldpos - old_file_size, new_buf.data(), new_buf.size(),
           std::bind(&BsdiffPatchReader::ReadDiffStream, &patch_reader,
                     std::placeholders::_1, std::placeholders::_2));
       if (ret)
         return ret;
       seek_offset = 0;
     }

     // We just checked that |seek_offset| is not negative.
     if (static_cast<uint64_t>(seek_offset) != old_file_pos &&
         !old_file->Seek(seek_offset)) {
       PLOG(ERROR) << "Error seeking input file to offset: " << seek_offset;
       return 1;
     }

     old_file_pos =
         std::min<uint64_t>(oldpos + control_entry.diff_size, old_file_size);
     size_t chunk_size = old_file_pos - seek_offset;
     while (chunk_size > 0) {
       size_t read_bytes;
       size_t bytes_to_read = std::min(chunk_size, old_buf.size());
       if (!old_file->Read(old_buf.data(), bytes_to_read, &read_bytes)) {
         PLOG(ERROR) << "Error reading from input file.";
         return 1;
       }
       if (!read_bytes) {
         LOG(ERROR) << "EOF reached while reading from input file.";
         return 2;
       }
       // Read same amount of bytes from diff block
       if (!patch_reader.ReadDiffStream(new_buf.data(), read_bytes)) {
         LOG(ERROR) << "Failed to read diff stream.";
         return 2;
       }
       // new_buf already has data from diff block, adds old data to it.
       for (size_t k = 0; k < read_bytes; k++)
         new_buf[k] += old_buf[k];
       if (!WriteAll(new_file, new_buf.data(), read_bytes)) {
         PLOG(ERROR) << "Error writing to new file.";
         return 1;
       }
       chunk_size -= read_bytes;
     }

     // Adjust pointers.
     newpos += control_entry.diff_size;
     if (oldpos > INT64_MAX - static_cast<int64_t>(control_entry.diff_size))
       return 2;
     oldpos += control_entry.diff_size;

     if (oldpos > static_cast<int64_t>(old_file_size)) {
       // Write diff block directly to new file without adding old data,
       // because we skipped part where |oldpos| > old_file_size.
       ret = ReadStreamAndWriteAll(
           new_file, oldpos - old_file_size, new_buf.data(), new_buf.size(),
           std::bind(&BsdiffPatchReader::ReadDiffStream, &patch_reader,
                     std::placeholders::_1, std::placeholders::_2));
       if (ret)
         return ret;
     }

     // Sanity-check.
     if (newpos + control_entry.extra_size > patch_reader.new_file_size()) {
       LOG(ERROR) << "Corrupt patch.";
       return 2;
     }

     // Read extra block.
     ret = ReadStreamAndWriteAll(
         new_file, control_entry.extra_size, new_buf.data(), new_buf.size(),
         std::bind(&BsdiffPatchReader::ReadExtraStream, &patch_reader,
                   std::placeholders::_1, std::placeholders::_2));
     if (ret)
       return ret;

     // Adjust pointers.
     newpos += control_entry.extra_size;
     if (control_entry.offset_increment > 0 &&
         oldpos > INT64_MAX - control_entry.offset_increment)
       return 2;
     oldpos += control_entry.offset_increment;
   }

   // Close input file.
   old_file->Close();

   if (!patch_reader.Finish()) {
     LOG(ERROR) << "Failed to finish the patch reader.";
     return 2;
   }

   if (!new_file->Close()) {
     PLOG(ERROR) << "Error closing new file.";
     return 1;
   }

   return 0;
 }

 }  // namespace bsdiff
	/*-
	* Copyright 2003-2005 Colin Percival
	* All rights reserved
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted providing that the following conditions
	* are met:
	* 1. Redistributions of source code must retain the above copyright
	* notice, this list of conditions and the following disclaimer.
	* 2. 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.
	*
	* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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.
	*/

	#if 0
	__FBSDID("$FreeBSD: src/usr.bin/bsdiff/bspatch/bspatch.c,v 1.1 2005/08/06 01:59:06 cperciva Exp $");
	#endif

	#include "bsdiff/bspatch.h"

	#include <errno.h>
	#include <fcntl.h>
	#include <inttypes.h>
	#include <stdio.h>
	#include <stdint.h>
	#include <stdlib.h>
	#include <string.h>
	#include <sys/stat.h>
	#include <sys/types.h>
	#include <unistd.h>

	#include <algorithm>
	#include <memory>
	#include <vector>

	#include "bsdiff/buffer_file.h"
	#include "bsdiff/control_entry.h"
	#include "bsdiff/extents.h"
	#include "bsdiff/extents_file.h"
	#include "bsdiff/file.h"
	#include "bsdiff/file_interface.h"
	#include "bsdiff/logging.h"
	#include "bsdiff/memory_file.h"
	#include "bsdiff/patch_reader.h"
	#include "bsdiff/sink_file.h"
	#include "bsdiff/utils.h"

	namespace {
	// Read the data in \|stream\| and write \|size\| decompressed data to \|file\|;
	// using the buffer in \|buf\| with size \|buf_size\|.
	// Returns 0 on success, 1 on I/O error and 2 on data error.
	int ReadStreamAndWriteAll(
	const std::unique_ptr<bsdiff::FileInterface>& file,
	size_t size,
	uint8_t* buf,
	size_t buf_size,
	const std::function<bool(uint8_t*, size_t)>& read_func) {
	while (size > 0) {
	size_t bytes_to_output = std::min(size, buf_size);
	if (!read_func(buf, bytes_to_output)) {
	LOG(ERROR) << "Failed to read stream.";
	return 2;
	}

	if (!WriteAll(file, buf, bytes_to_output)) {
	PLOG(ERROR) << "WriteAll() failed.";
	return 1;
	}
	size -= bytes_to_output;
	}
	return 0;
	}

	} // namespace

	namespace bsdiff {

	bool ReadAll(const std::unique_ptr<FileInterface>& file,
	uint8_t* data,
	size_t size) {
	size_t offset = 0, read;
	while (offset < size) {
	if (!file->Read(data + offset, size - offset, &read) \|\| read == 0)
	return false;
	offset += read;
	}
	return true;
	}

	bool WriteAll(const std::unique_ptr<FileInterface>& file,
	const uint8_t* data,
	size_t size) {
	size_t offset = 0, written;
	while (offset < size) {
	if (!file->Write(data + offset, size - offset, &written) \|\| written == 0)
	return false;
	offset += written;
	}
	return true;
	}

	bool IsOverlapping(const char* old_filename,
	const char* new_filename,
	const std::vector<ex_t>& old_extents,
	const std::vector<ex_t>& new_extents) {
	struct stat old_stat, new_stat;
	if (stat(new_filename, &new_stat) == -1) {
	if (errno == ENOENT)
	return false;
	PLOG(ERROR) << "Error stat the new file: " << new_filename;
	return true;
	}
	if (stat(old_filename, &old_stat) == -1) {
	PLOG(ERROR) << "Error stat the old file: " << old_filename;
	return true;
	}

	if (old_stat.st_dev != new_stat.st_dev \|\| old_stat.st_ino != new_stat.st_ino)
	return false;

	if (old_extents.empty() && new_extents.empty())
	return true;

	for (ex_t old_ex : old_extents)
	for (ex_t new_ex : new_extents)
	if (static_cast<uint64_t>(old_ex.off) < new_ex.off + new_ex.len &&
	static_cast<uint64_t>(new_ex.off) < old_ex.off + old_ex.len)
	return true;

	return false;
	}

	// Patch \|old_filename\| with \|patch_filename\| and save it to \|new_filename\|.
	// \|old_extents\| and \|new_extents\| are comma-separated lists of "offset:length"
	// extents of \|old_filename\| and \|new_filename\|.
	// Returns 0 on success, 1 on I/O error and 2 on data error.
	int bspatch(const char* old_filename,
	const char* new_filename,
	const char* patch_filename,
	const char* old_extents,
	const char* new_extents) {
	std::unique_ptr<FileInterface> patch_file =
	File::FOpen(patch_filename, O_RDONLY);
	if (!patch_file) {
	PLOG(ERROR) << "Error opening the patch file: " << patch_filename;
	return 1;
	}
	uint64_t patch_size;
	patch_file->GetSize(&patch_size);
	std::vector<uint8_t> patch(patch_size);
	if (!ReadAll(patch_file, patch.data(), patch_size)) {
	PLOG(ERROR) << "Error reading the patch file: " << patch_filename;
	return 1;
	}
	patch_file.reset();

	return bspatch(old_filename, new_filename, patch.data(), patch_size,
	old_extents, new_extents);
	}

	// Patch \|old_filename\| with \|patch_data\| and save it to \|new_filename\|.
	// \|old_extents\| and \|new_extents\| are comma-separated lists of "offset:length"
	// extents of \|old_filename\| and \|new_filename\|.
	// Returns 0 on success, 1 on I/O error and 2 on data error.
	int bspatch(const char* old_filename,
	const char* new_filename,
	const uint8_t* patch_data,
	size_t patch_size,
	const char* old_extents,
	const char* new_extents) {
	int using_extents = (old_extents != NULL \|\| new_extents != NULL);

	// Open input file for reading.
	std::unique_ptr<FileInterface> old_file = File::FOpen(old_filename, O_RDONLY);
	if (!old_file) {
	PLOG(ERROR) << "Error opening the old file: " << old_filename;
	return 1;
	}

	std::vector<ex_t> parsed_old_extents;
	if (using_extents) {
	if (!ParseExtentStr(old_extents, &parsed_old_extents)) {
	LOG(ERROR) << "Error parsing the old extents.";
	return 2;
	}
	old_file.reset(new ExtentsFile(std::move(old_file), parsed_old_extents));
	}

	// Open output file for writing.
	std::unique_ptr<FileInterface> new_file =
	File::FOpen(new_filename, O_CREAT \| O_WRONLY);
	if (!new_file) {
	PLOG(ERROR) << "Error opening the new file: " << new_filename;
	return 1;
	}

	std::vector<ex_t> parsed_new_extents;
	if (using_extents) {
	if (!ParseExtentStr(new_extents, &parsed_new_extents)) {
	LOG(ERROR) << "Error parsing the new extents.";
	return 2;
	}
	new_file.reset(new ExtentsFile(std::move(new_file), parsed_new_extents));
	}

	if (IsOverlapping(old_filename, new_filename, parsed_old_extents,
	parsed_new_extents)) {
	// New and old file is overlapping, we can not stream output to new file,
	// cache it in a buffer and write to the file at the end.
	uint64_t newsize = ParseInt64(patch_data + 24);
	new_file.reset(new BufferFile(std::move(new_file), newsize));
	}

	return bspatch(old_file, new_file, patch_data, patch_size);
	}

	// Patch \|old_data\| with \|patch_data\| and save it by calling sink function.
	// Returns 0 on success, 1 on I/O error and 2 on data error.
	int bspatch(const uint8_t* old_data,
	size_t old_size,
	const uint8_t* patch_data,
	size_t patch_size,
	const sink_func& sink) {
	std::unique_ptr<FileInterface> old_file(new MemoryFile(old_data, old_size));
	std::unique_ptr<FileInterface> new_file(new SinkFile(sink));

	return bspatch(old_file, new_file, patch_data, patch_size);
	}

	// Patch \|old_file\| with \|patch_data\| and save it to \|new_file\|.
	// Returns 0 on success, 1 on I/O error and 2 on data error.
	int bspatch(const std::unique_ptr<FileInterface>& old_file,
	const std::unique_ptr<FileInterface>& new_file,
	const uint8_t* patch_data,
	size_t patch_size) {
	BsdiffPatchReader patch_reader;
	if (!patch_reader.Init(patch_data, patch_size)) {
	LOG(ERROR) << "Failed to initialize patch reader.";
	return 2;
	}

	uint64_t old_file_size;
	if (!old_file->GetSize(&old_file_size)) {
	LOG(ERROR) << "Cannot obtain the size of old file.";
	return 1;
	}

	// The oldpos can be negative, but the new pos is only incremented linearly.
	int64_t oldpos = 0;
	uint64_t newpos = 0;
	std::vector<uint8_t> old_buf(1024 * 1024);
	std::vector<uint8_t> new_buf(1024 * 1024);
	uint64_t old_file_pos = 0;
	while (newpos < patch_reader.new_file_size()) {
	ControlEntry control_entry(0, 0, 0);
	if (!patch_reader.ParseControlEntry(&control_entry)) {
	LOG(ERROR) << "Failed to read control stream.";
	return 2;
	}

	// Sanity-check.
	if (newpos + control_entry.diff_size > patch_reader.new_file_size()) {
	LOG(ERROR) << "Corrupt patch.";
	return 2;
	}

	int ret = 0;
	// Add old data to diff string. It is enough to fseek once, at
	// the beginning of the sequence, to avoid unnecessary overhead.
	int64_t seek_offset = oldpos;
	if (seek_offset < 0) {
	// Write diff block directly to new file without adding old data,
	// because we will skip part where \|oldpos\| < 0.
	ret = ReadStreamAndWriteAll(
	new_file, oldpos - old_file_size, new_buf.data(), new_buf.size(),
	std::bind(&BsdiffPatchReader::ReadDiffStream, &patch_reader,
	std::placeholders::_1, std::placeholders::_2));
	if (ret)
	return ret;
	seek_offset = 0;
	}

	// We just checked that \|seek_offset\| is not negative.
	if (static_cast<uint64_t>(seek_offset) != old_file_pos &&
	!old_file->Seek(seek_offset)) {
	PLOG(ERROR) << "Error seeking input file to offset: " << seek_offset;
	return 1;
	}

	old_file_pos =
	std::min<uint64_t>(oldpos + control_entry.diff_size, old_file_size);
	size_t chunk_size = old_file_pos - seek_offset;
	while (chunk_size > 0) {
	size_t read_bytes;
	size_t bytes_to_read = std::min(chunk_size, old_buf.size());
	if (!old_file->Read(old_buf.data(), bytes_to_read, &read_bytes)) {
	PLOG(ERROR) << "Error reading from input file.";
	return 1;
	}
	if (!read_bytes) {
	LOG(ERROR) << "EOF reached while reading from input file.";
	return 2;
	}
	// Read same amount of bytes from diff block
	if (!patch_reader.ReadDiffStream(new_buf.data(), read_bytes)) {
	LOG(ERROR) << "Failed to read diff stream.";
	return 2;
	}
	// new_buf already has data from diff block, adds old data to it.
	for (size_t k = 0; k < read_bytes; k++)
	new_buf[k] += old_buf[k];
	if (!WriteAll(new_file, new_buf.data(), read_bytes)) {
	PLOG(ERROR) << "Error writing to new file.";
	return 1;
	}
	chunk_size -= read_bytes;
	}

	// Adjust pointers.
	newpos += control_entry.diff_size;
	if (oldpos > INT64_MAX - static_cast<int64_t>(control_entry.diff_size))
	return 2;
	oldpos += control_entry.diff_size;

	if (oldpos > static_cast<int64_t>(old_file_size)) {
	// Write diff block directly to new file without adding old data,
	// because we skipped part where \|oldpos\| > old_file_size.
	ret = ReadStreamAndWriteAll(
	new_file, oldpos - old_file_size, new_buf.data(), new_buf.size(),
	std::bind(&BsdiffPatchReader::ReadDiffStream, &patch_reader,
	std::placeholders::_1, std::placeholders::_2));
	if (ret)
	return ret;
	}

	// Sanity-check.
	if (newpos + control_entry.extra_size > patch_reader.new_file_size()) {
	LOG(ERROR) << "Corrupt patch.";
	return 2;
	}

	// Read extra block.
	ret = ReadStreamAndWriteAll(
	new_file, control_entry.extra_size, new_buf.data(), new_buf.size(),
	std::bind(&BsdiffPatchReader::ReadExtraStream, &patch_reader,
	std::placeholders::_1, std::placeholders::_2));
	if (ret)
	return ret;

	// Adjust pointers.
	newpos += control_entry.extra_size;
	if (control_entry.offset_increment > 0 &&
	oldpos > INT64_MAX - control_entry.offset_increment)
	return 2;
	oldpos += control_entry.offset_increment;
	}

	// Close input file.
	old_file->Close();

	if (!patch_reader.Finish()) {
	LOG(ERROR) << "Failed to finish the patch reader.";
	return 2;
	}

	if (!new_file->Close()) {
	PLOG(ERROR) << "Error closing new file.";
	return 1;
	}

	return 0;
	}

	} // namespace bsdiff