applypatch/applypatch.cpp - android_bootable_recovery - Gitiles

 /*
  * Copyright (C) 2008 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 #include "applypatch/applypatch.h"

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

 #include <algorithm>
 #include <functional>
 #include <memory>
 #include <string>
 #include <utility>
 #include <vector>

 #include <android-base/file.h>
 #include <android-base/logging.h>
 #include <android-base/parseint.h>
 #include <android-base/strings.h>
 #include <android-base/unique_fd.h>
 #include <openssl/sha.h>

 #include "edify/expr.h"
 #include "otautil/paths.h"
 #include "otautil/print_sha1.h"

 static int LoadPartitionContents(const std::string& filename, FileContents* file);
 static int GenerateTarget(const FileContents& source_file, const std::unique_ptr<Value>& patch,
                           const std::string& target_filename,
                           const uint8_t target_sha1[SHA_DIGEST_LENGTH], const Value* bonus_data);

 int LoadFileContents(const std::string& filename, FileContents* file) {
   // A special 'filename' beginning with "EMMC:" means to load the contents of a partition.
   if (android::base::StartsWith(filename, "EMMC:")) {
     return LoadPartitionContents(filename, file);
   }

   std::string data;
   if (!android::base::ReadFileToString(filename, &data)) {
     PLOG(ERROR) << "Failed to read \"" << filename << "\"";
     return -1;
   }

   file->data = std::vector<unsigned char>(data.begin(), data.end());
   SHA1(file->data.data(), file->data.size(), file->sha1);
   return 0;
 }

 // Loads the contents of an EMMC partition into the provided FileContents. filename should be a
 // string of the form "EMMC:<partition_device>:...". The smallest size_n bytes for which that prefix
 // of the partition contents has the corresponding sha1 hash will be loaded. It is acceptable for a
 // size value to be repeated with different sha1s. Returns 0 on success.
 //
 // This complexity is needed because if an OTA installation is interrupted, the partition might
 // contain either the source or the target data, which might be of different lengths. We need to
 // know the length in order to read from a partition (there is no "end-of-file" marker), so the
 // caller must specify the possible lengths and the hash of the data, and we'll do the load
 // expecting to find one of those hashes.
 static int LoadPartitionContents(const std::string& filename, FileContents* file) {
   std::vector<std::string> pieces = android::base::Split(filename, ":");
   if (pieces.size() < 4 || pieces.size() % 2 != 0 || pieces[0] != "EMMC") {
     LOG(ERROR) << "LoadPartitionContents called with bad filename \"" << filename << "\"";
     return -1;
   }

   size_t pair_count = (pieces.size() - 2) / 2;  // # of (size, sha1) pairs in filename
   std::vector<std::pair<size_t, std::string>> pairs;
   for (size_t i = 0; i < pair_count; ++i) {
     size_t size;
     if (!android::base::ParseUint(pieces[i * 2 + 2], &size) || size == 0) {
       LOG(ERROR) << "LoadPartitionContents called with bad size \"" << pieces[i * 2 + 2] << "\"";
       return -1;
     }
     pairs.push_back({ size, pieces[i * 2 + 3] });
   }

   // Sort the pairs array so that they are in order of increasing size.
   std::sort(pairs.begin(), pairs.end());

   const char* partition = pieces[1].c_str();
   android::base::unique_fd dev(open(partition, O_RDONLY));
   if (dev == -1) {
     PLOG(ERROR) << "Failed to open eMMC partition \"" << partition << "\"";
     return -1;
   }

   SHA_CTX sha_ctx;
   SHA1_Init(&sha_ctx);

   // Allocate enough memory to hold the largest size.
   std::vector<unsigned char> buffer(pairs[pair_count - 1].first);
   size_t offset = 0;  // # bytes read so far
   bool found = false;

   for (const auto& pair : pairs) {
     size_t current_size = pair.first;
     const std::string& current_sha1 = pair.second;

     // Read enough additional bytes to get us up to the next size. (Again,
     // we're trying the possibilities in order of increasing size).
     if (current_size - offset > 0) {
       if (!android::base::ReadFully(dev, buffer.data() + offset, current_size - offset)) {
         PLOG(ERROR) << "Failed to read " << current_size - offset << " bytes of data at offset "
                     << offset << " for partition " << partition;
         return -1;
       }

       SHA1_Update(&sha_ctx, buffer.data() + offset, current_size - offset);
       offset = current_size;
     }
     // Duplicate the SHA context and finalize the duplicate so we can
     // check it against this pair's expected hash.
     SHA_CTX temp_ctx;
     memcpy(&temp_ctx, &sha_ctx, sizeof(SHA_CTX));
     uint8_t sha_so_far[SHA_DIGEST_LENGTH];
     SHA1_Final(sha_so_far, &temp_ctx);

     uint8_t parsed_sha[SHA_DIGEST_LENGTH];
     if (ParseSha1(current_sha1, parsed_sha) != 0) {
       LOG(ERROR) << "Failed to parse SHA-1 \"" << current_sha1 << "\" in " << filename;
       return -1;
     }

     if (memcmp(sha_so_far, parsed_sha, SHA_DIGEST_LENGTH) == 0) {
       // We have a match. Stop reading the partition; we'll return the data we've read so far.
       LOG(INFO) << "Partition read matched size " << current_size << " SHA-1 " << current_sha1;
       found = true;
       break;
     }
   }

   if (!found) {
     // Ran off the end of the list of (size, sha1) pairs without finding a match.
     LOG(ERROR) << "Contents of partition \"" << partition << "\" didn't match " << filename;
     return -1;
   }

   SHA1_Final(file->sha1, &sha_ctx);

   buffer.resize(offset);
   file->data = std::move(buffer);

   return 0;
 }

 int SaveFileContents(const std::string& filename, const FileContents* file) {
   android::base::unique_fd fd(
       open(filename.c_str(), O_WRONLY | O_CREAT | O_TRUNC | O_SYNC, S_IRUSR | S_IWUSR));
   if (fd == -1) {
     PLOG(ERROR) << "Failed to open \"" << filename << "\" for write";
     return -1;
   }

   if (!android::base::WriteFully(fd, file->data.data(), file->data.size())) {
     PLOG(ERROR) << "Failed to write " << file->data.size() << " bytes of data to " << filename;
     return -1;
   }

   if (fsync(fd) != 0) {
     PLOG(ERROR) << "Failed to fsync \"" << filename << "\"";
     return -1;
   }

   if (close(fd.release()) != 0) {
     PLOG(ERROR) << "Failed to close \"" << filename << "\"";
     return -1;
   }

   return 0;
 }

 // Writes a memory buffer to 'target' partition, a string of the form
 // "EMMC:<partition_device>[:...]". The target name might contain multiple colons, but
 // WriteToPartition() only uses the first two and ignores the rest. Returns 0 on success.
 static int WriteToPartition(const unsigned char* data, size_t len, const std::string& target) {
   std::vector<std::string> pieces = android::base::Split(target, ":");
   if (pieces.size() < 2 || pieces[0] != "EMMC") {
     LOG(ERROR) << "WriteToPartition called with bad target \"" << target << "\"";
     return -1;
   }

   size_t start = 0;
   bool success = false;
   for (size_t attempt = 0; attempt < 2; ++attempt) {
     std::string partition = pieces[1];
     android::base::unique_fd fd(open(partition.c_str(), O_RDWR));
     if (fd == -1) {
       PLOG(ERROR) << "Failed to open \"" << partition << "\"";
       return -1;
     }

     if (TEMP_FAILURE_RETRY(lseek(fd, start, SEEK_SET)) == -1) {
       PLOG(ERROR) << "Failed to seek to " << start << " on \"" << partition << "\"";
       return -1;
     }

     if (!android::base::WriteFully(fd, data + start, len - start)) {
       PLOG(ERROR) << "Failed to write " << len - start << " bytes to \"" << partition << "\"";
       return -1;
     }

     if (fsync(fd) != 0) {
       PLOG(ERROR) << "Failed to sync \"" << partition << "\"";
       return -1;
     }
     if (close(fd.release()) != 0) {
       PLOG(ERROR) << "Failed to close \"" << partition << "\"";
       return -1;
     }

     fd.reset(open(partition.c_str(), O_RDONLY));
     if (fd == -1) {
       PLOG(ERROR) << "Failed to reopen \"" << partition << "\" for verification";
       return -1;
     }

     // Drop caches so our subsequent verification read won't just be reading the cache.
     sync();
     std::string drop_cache = "/proc/sys/vm/drop_caches";
     if (!android::base::WriteStringToFile("3\n", drop_cache)) {
       PLOG(ERROR) << "Failed to write to " << drop_cache;
     } else {
       LOG(INFO) << "  caches dropped";
     }
     sleep(1);

     // Verify.
     if (TEMP_FAILURE_RETRY(lseek(fd, 0, SEEK_SET)) == -1) {
       PLOG(ERROR) << "Failed to seek to 0 on " << partition;
       return -1;
     }

     unsigned char buffer[4096];
     start = len;
     for (size_t p = 0; p < len; p += sizeof(buffer)) {
       size_t to_read = len - p;
       if (to_read > sizeof(buffer)) {
         to_read = sizeof(buffer);
       }

       if (!android::base::ReadFully(fd, buffer, to_read)) {
         PLOG(ERROR) << "Failed to verify-read " << partition << " at " << p;
         return -1;
       }

       if (memcmp(buffer, data + p, to_read) != 0) {
         LOG(ERROR) << "Verification failed starting at " << p;
         start = p;
         break;
       }
     }

     if (start == len) {
       LOG(INFO) << "Verification read succeeded (attempt " << attempt + 1 << ")";
       success = true;
       break;
     }

     if (close(fd.release()) != 0) {
       PLOG(ERROR) << "Failed to close " << partition;
       return -1;
     }
   }

   if (!success) {
     LOG(ERROR) << "Failed to verify after all attempts";
     return -1;
   }

   sync();

   return 0;
 }

 int ParseSha1(const std::string& str, uint8_t* digest) {
   const char* ps = str.c_str();
   uint8_t* pd = digest;
   for (int i = 0; i < SHA_DIGEST_LENGTH * 2; ++i, ++ps) {
     int digit;
     if (*ps >= '0' && *ps <= '9') {
       digit = *ps - '0';
     } else if (*ps >= 'a' && *ps <= 'f') {
       digit = *ps - 'a' + 10;
     } else if (*ps >= 'A' && *ps <= 'F') {
       digit = *ps - 'A' + 10;
     } else {
       return -1;
     }
     if (i % 2 == 0) {
       *pd = digit << 4;
     } else {
       *pd |= digit;
       ++pd;
     }
   }
   if (*ps != '\0') return -1;
   return 0;
 }

 // Searches a vector of SHA-1 strings for one matching the given SHA-1. Returns the index of the
 // match on success, or -1 if no match is found.
 static int FindMatchingPatch(const uint8_t* sha1, const std::vector<std::string>& patch_sha1s) {
   for (size_t i = 0; i < patch_sha1s.size(); ++i) {
     uint8_t patch_sha1[SHA_DIGEST_LENGTH];
     if (ParseSha1(patch_sha1s[i], patch_sha1) == 0 &&
         memcmp(patch_sha1, sha1, SHA_DIGEST_LENGTH) == 0) {
       return i;
     }
   }
   return -1;
 }

 int applypatch_check(const std::string& filename, const std::vector<std::string>& sha1s) {
   if (!android::base::StartsWith(filename, "EMMC:")) {
     return 1;
   }

   // The check will pass if LoadPartitionContents is successful, because the filename already
   // encodes the desired SHA-1s.
   FileContents file;
   if (LoadPartitionContents(filename, &file) != 0) {
     LOG(INFO) << "\"" << filename << "\" doesn't have any of expected SHA-1 sums; checking cache";

     // If the partition is corrupted, it might be because we were killed in the middle of patching
     // it. A copy should have been made in cache_temp_source. If that file exists and matches the
     // SHA-1 we're looking for, the check still passes.
     if (LoadFileContents(Paths::Get().cache_temp_source(), &file) != 0) {
       LOG(ERROR) << "Failed to load cache file";
       return 1;
     }

     if (FindMatchingPatch(file.sha1, sha1s) < 0) {
       LOG(ERROR) << "The cache bits don't match any SHA-1 for \"" << filename << "\"";
       return 1;
     }
   }
   return 0;
 }

 int ShowLicenses() {
   ShowBSDiffLicense();
   return 0;
 }

 int applypatch(const char* source_filename, const char* target_filename,
                const char* target_sha1_str, size_t /* target_size */,
                const std::vector<std::string>& patch_sha1s,
                const std::vector<std::unique_ptr<Value>>& patch_data, const Value* bonus_data) {
   LOG(INFO) << "Patching " << source_filename;

   if (target_filename[0] == '-' && target_filename[1] == '\0') {
     target_filename = source_filename;
   }

   if (strncmp(target_filename, "EMMC:", 5) != 0) {
     LOG(ERROR) << "Supporting patching EMMC targets only";
     return 1;
   }

   uint8_t target_sha1[SHA_DIGEST_LENGTH];
   if (ParseSha1(target_sha1_str, target_sha1) != 0) {
     LOG(ERROR) << "Failed to parse target SHA-1 \"" << target_sha1_str << "\"";
     return 1;
   }

   // We try to load the target file into the source_file object.
   FileContents source_file;
   if (LoadFileContents(target_filename, &source_file) == 0) {
     if (memcmp(source_file.sha1, target_sha1, SHA_DIGEST_LENGTH) == 0) {
       // The early-exit case: the patch was already applied, this file has the desired hash, nothing
       // for us to do.
       LOG(INFO) << "  already " << short_sha1(target_sha1);
       return 0;
     }
   }

   if (source_file.data.empty() ||
       (target_filename != source_filename && strcmp(target_filename, source_filename) != 0)) {
     // Need to load the source file: either we failed to load the target file, or we did but it's
     // different from the expected.
     source_file.data.clear();
     LoadFileContents(source_filename, &source_file);
   }

   if (!source_file.data.empty()) {
     int to_use = FindMatchingPatch(source_file.sha1, patch_sha1s);
     if (to_use != -1) {
       return GenerateTarget(source_file, patch_data[to_use], target_filename, target_sha1,
                             bonus_data);
     }
   }

   LOG(INFO) << "Source file is bad; trying copy";

   FileContents copy_file;
   if (LoadFileContents(Paths::Get().cache_temp_source(), &copy_file) < 0) {
     LOG(ERROR) << "Failed to read copy file";
     return 1;
   }

   int to_use = FindMatchingPatch(copy_file.sha1, patch_sha1s);
   if (to_use == -1) {
     LOG(ERROR) << "The copy on /cache doesn't match source SHA-1s either";
     return 1;
   }

   return GenerateTarget(copy_file, patch_data[to_use], target_filename, target_sha1, bonus_data);
 }

 int applypatch_flash(const char* source_filename, const char* target_filename,
                      const char* target_sha1_str, size_t target_size) {
   LOG(INFO) << "Flashing " << target_filename;

   uint8_t target_sha1[SHA_DIGEST_LENGTH];
   if (ParseSha1(target_sha1_str, target_sha1) != 0) {
     LOG(ERROR) << "Failed to parse target SHA-1 \"" << target_sha1_str << "\"";
     return 1;
   }

   std::vector<std::string> pieces = android::base::Split(target_filename, ":");
   if (pieces.size() != 4 || pieces[0] != "EMMC") {
     LOG(ERROR) << "Invalid target name \"" << target_filename << "\"";
     return 1;
   }

   // Load the target into the source_file object to see if already applied.
   FileContents source_file;
   if (LoadPartitionContents(target_filename, &source_file) == 0 &&
       memcmp(source_file.sha1, target_sha1, SHA_DIGEST_LENGTH) == 0) {
     // The early-exit case: the image was already applied, this partition has the desired hash,
     // nothing for us to do.
     LOG(INFO) << "  already " << short_sha1(target_sha1);
     return 0;
   }

   if (LoadFileContents(source_filename, &source_file) == 0) {
     if (memcmp(source_file.sha1, target_sha1, SHA_DIGEST_LENGTH) != 0) {
       // The source doesn't have desired checksum.
       LOG(ERROR) << "source \"" << source_filename << "\" doesn't have expected SHA-1 sum";
       LOG(ERROR) << "expected: " << short_sha1(target_sha1)
                  << ", found: " << short_sha1(source_file.sha1);
       return 1;
     }
   }

   if (WriteToPartition(source_file.data.data(), target_size, target_filename) != 0) {
     LOG(ERROR) << "Failed to write copied data to " << target_filename;
     return 1;
   }
   return 0;
 }

 static int GenerateTarget(const FileContents& source_file, const std::unique_ptr<Value>& patch,
                           const std::string& target_filename,
                           const uint8_t target_sha1[SHA_DIGEST_LENGTH], const Value* bonus_data) {
   if (patch->type != Value::Type::BLOB) {
     LOG(ERROR) << "patch is not a blob";
     return 1;
   }

   const char* header = &patch->data[0];
   size_t header_bytes_read = patch->data.size();
   bool use_bsdiff = false;
   if (header_bytes_read >= 8 && memcmp(header, "BSDIFF40", 8) == 0) {
     use_bsdiff = true;
   } else if (header_bytes_read >= 8 && memcmp(header, "IMGDIFF2", 8) == 0) {
     use_bsdiff = false;
   } else {
     LOG(ERROR) << "Unknown patch file format";
     return 1;
   }

   CHECK(android::base::StartsWith(target_filename, "EMMC:"));

   // We write the original source to cache, in case the partition write is interrupted.
   if (!CheckAndFreeSpaceOnCache(source_file.data.size())) {
     LOG(ERROR) << "Not enough free space on /cache";
     return 1;
   }
   if (SaveFileContents(Paths::Get().cache_temp_source(), &source_file) < 0) {
     LOG(ERROR) << "Failed to back up source file";
     return 1;
   }

   // We store the decoded output in memory.
   std::string memory_sink_str;  // Don't need to reserve space.
   SHA_CTX ctx;
   SHA1_Init(&ctx);
   SinkFn sink = [&memory_sink_str, &ctx](const unsigned char* data, size_t len) {
     SHA1_Update(&ctx, data, len);
     memory_sink_str.append(reinterpret_cast<const char*>(data), len);
     return len;
   };

   int result;
   if (use_bsdiff) {
     result = ApplyBSDiffPatch(source_file.data.data(), source_file.data.size(), *patch, 0, sink);
   } else {
     result =
         ApplyImagePatch(source_file.data.data(), source_file.data.size(), *patch, sink, bonus_data);
   }

   if (result != 0) {
     LOG(ERROR) << "Failed to apply the patch: " << result;
     return 1;
   }

   uint8_t current_target_sha1[SHA_DIGEST_LENGTH];
   SHA1_Final(current_target_sha1, &ctx);
   if (memcmp(current_target_sha1, target_sha1, SHA_DIGEST_LENGTH) != 0) {
     LOG(ERROR) << "Patching did not produce the expected SHA-1 of " << short_sha1(target_sha1);

     LOG(ERROR) << "target size " << memory_sink_str.size() << " SHA-1 "
                << short_sha1(current_target_sha1);
     LOG(ERROR) << "source size " << source_file.data.size() << " SHA-1 "
                << short_sha1(source_file.sha1);

     uint8_t patch_digest[SHA_DIGEST_LENGTH];
     SHA1(reinterpret_cast<const uint8_t*>(patch->data.data()), patch->data.size(), patch_digest);
     LOG(ERROR) << "patch size " << patch->data.size() << " SHA-1 " << short_sha1(patch_digest);

     if (bonus_data != nullptr) {
       uint8_t bonus_digest[SHA_DIGEST_LENGTH];
       SHA1(reinterpret_cast<const uint8_t*>(bonus_data->data.data()), bonus_data->data.size(),
            bonus_digest);
       LOG(ERROR) << "bonus size " << bonus_data->data.size() << " SHA-1 "
                  << short_sha1(bonus_digest);
     }

     return 1;
   } else {
     LOG(INFO) << "  now " << short_sha1(target_sha1);
   }

   // Write back the temp file to the partition.
   if (WriteToPartition(reinterpret_cast<const unsigned char*>(memory_sink_str.c_str()),
                        memory_sink_str.size(), target_filename) != 0) {
     LOG(ERROR) << "Failed to write patched data to " << target_filename;
     return 1;
   }

   // Delete the backup copy of the source.
   unlink(Paths::Get().cache_temp_source().c_str());

   // Success!
   return 0;
 }
	/*
	* Copyright (C) 2008 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	#include "applypatch/applypatch.h"

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

	#include <algorithm>
	#include <functional>
	#include <memory>
	#include <string>
	#include <utility>
	#include <vector>

	#include <android-base/file.h>
	#include <android-base/logging.h>
	#include <android-base/parseint.h>
	#include <android-base/strings.h>
	#include <android-base/unique_fd.h>
	#include <openssl/sha.h>

	#include "edify/expr.h"
	#include "otautil/paths.h"
	#include "otautil/print_sha1.h"

	static int LoadPartitionContents(const std::string& filename, FileContents* file);
	static int GenerateTarget(const FileContents& source_file, const std::unique_ptr<Value>& patch,
	const std::string& target_filename,
	const uint8_t target_sha1[SHA_DIGEST_LENGTH], const Value* bonus_data);

	int LoadFileContents(const std::string& filename, FileContents* file) {
	// A special 'filename' beginning with "EMMC:" means to load the contents of a partition.
	if (android::base::StartsWith(filename, "EMMC:")) {
	return LoadPartitionContents(filename, file);
	}

	std::string data;
	if (!android::base::ReadFileToString(filename, &data)) {
	PLOG(ERROR) << "Failed to read \"" << filename << "\"";
	return -1;
	}

	file->data = std::vector<unsigned char>(data.begin(), data.end());
	SHA1(file->data.data(), file->data.size(), file->sha1);
	return 0;
	}

	// Loads the contents of an EMMC partition into the provided FileContents. filename should be a
	// string of the form "EMMC:<partition_device>:...". The smallest size_n bytes for which that prefix
	// of the partition contents has the corresponding sha1 hash will be loaded. It is acceptable for a
	// size value to be repeated with different sha1s. Returns 0 on success.
	//
	// This complexity is needed because if an OTA installation is interrupted, the partition might
	// contain either the source or the target data, which might be of different lengths. We need to
	// know the length in order to read from a partition (there is no "end-of-file" marker), so the
	// caller must specify the possible lengths and the hash of the data, and we'll do the load
	// expecting to find one of those hashes.
	static int LoadPartitionContents(const std::string& filename, FileContents* file) {
	std::vector<std::string> pieces = android::base::Split(filename, ":");
	if (pieces.size() < 4 \|\| pieces.size() % 2 != 0 \|\| pieces[0] != "EMMC") {
	LOG(ERROR) << "LoadPartitionContents called with bad filename \"" << filename << "\"";
	return -1;
	}

	size_t pair_count = (pieces.size() - 2) / 2; // # of (size, sha1) pairs in filename
	std::vector<std::pair<size_t, std::string>> pairs;
	for (size_t i = 0; i < pair_count; ++i) {
	size_t size;
	if (!android::base::ParseUint(pieces[i * 2 + 2], &size) \|\| size == 0) {
	LOG(ERROR) << "LoadPartitionContents called with bad size \"" << pieces[i * 2 + 2] << "\"";
	return -1;
	}
	pairs.push_back({ size, pieces[i * 2 + 3] });
	}

	// Sort the pairs array so that they are in order of increasing size.
	std::sort(pairs.begin(), pairs.end());

	const char* partition = pieces[1].c_str();
	android::base::unique_fd dev(open(partition, O_RDONLY));
	if (dev == -1) {
	PLOG(ERROR) << "Failed to open eMMC partition \"" << partition << "\"";
	return -1;
	}

	SHA_CTX sha_ctx;
	SHA1_Init(&sha_ctx);

	// Allocate enough memory to hold the largest size.
	std::vector<unsigned char> buffer(pairs[pair_count - 1].first);
	size_t offset = 0; // # bytes read so far
	bool found = false;

	for (const auto& pair : pairs) {
	size_t current_size = pair.first;
	const std::string& current_sha1 = pair.second;

	// Read enough additional bytes to get us up to the next size. (Again,
	// we're trying the possibilities in order of increasing size).
	if (current_size - offset > 0) {
	if (!android::base::ReadFully(dev, buffer.data() + offset, current_size - offset)) {
	PLOG(ERROR) << "Failed to read " << current_size - offset << " bytes of data at offset "
	<< offset << " for partition " << partition;
	return -1;
	}

	SHA1_Update(&sha_ctx, buffer.data() + offset, current_size - offset);
	offset = current_size;
	}
	// Duplicate the SHA context and finalize the duplicate so we can
	// check it against this pair's expected hash.
	SHA_CTX temp_ctx;
	memcpy(&temp_ctx, &sha_ctx, sizeof(SHA_CTX));
	uint8_t sha_so_far[SHA_DIGEST_LENGTH];
	SHA1_Final(sha_so_far, &temp_ctx);

	uint8_t parsed_sha[SHA_DIGEST_LENGTH];
	if (ParseSha1(current_sha1, parsed_sha) != 0) {
	LOG(ERROR) << "Failed to parse SHA-1 \"" << current_sha1 << "\" in " << filename;
	return -1;
	}

	if (memcmp(sha_so_far, parsed_sha, SHA_DIGEST_LENGTH) == 0) {
	// We have a match. Stop reading the partition; we'll return the data we've read so far.
	LOG(INFO) << "Partition read matched size " << current_size << " SHA-1 " << current_sha1;
	found = true;
	break;
	}
	}

	if (!found) {
	// Ran off the end of the list of (size, sha1) pairs without finding a match.
	LOG(ERROR) << "Contents of partition \"" << partition << "\" didn't match " << filename;
	return -1;
	}

	SHA1_Final(file->sha1, &sha_ctx);

	buffer.resize(offset);
	file->data = std::move(buffer);

	return 0;
	}

	int SaveFileContents(const std::string& filename, const FileContents* file) {
	android::base::unique_fd fd(
	open(filename.c_str(), O_WRONLY \| O_CREAT \| O_TRUNC \| O_SYNC, S_IRUSR \| S_IWUSR));
	if (fd == -1) {
	PLOG(ERROR) << "Failed to open \"" << filename << "\" for write";
	return -1;
	}

	if (!android::base::WriteFully(fd, file->data.data(), file->data.size())) {
	PLOG(ERROR) << "Failed to write " << file->data.size() << " bytes of data to " << filename;
	return -1;
	}

	if (fsync(fd) != 0) {
	PLOG(ERROR) << "Failed to fsync \"" << filename << "\"";
	return -1;
	}

	if (close(fd.release()) != 0) {
	PLOG(ERROR) << "Failed to close \"" << filename << "\"";
	return -1;
	}

	return 0;
	}

	// Writes a memory buffer to 'target' partition, a string of the form
	// "EMMC:<partition_device>[:...]". The target name might contain multiple colons, but
	// WriteToPartition() only uses the first two and ignores the rest. Returns 0 on success.
	static int WriteToPartition(const unsigned char* data, size_t len, const std::string& target) {
	std::vector<std::string> pieces = android::base::Split(target, ":");
	if (pieces.size() < 2 \|\| pieces[0] != "EMMC") {
	LOG(ERROR) << "WriteToPartition called with bad target \"" << target << "\"";
	return -1;
	}

	size_t start = 0;
	bool success = false;
	for (size_t attempt = 0; attempt < 2; ++attempt) {
	std::string partition = pieces[1];
	android::base::unique_fd fd(open(partition.c_str(), O_RDWR));
	if (fd == -1) {
	PLOG(ERROR) << "Failed to open \"" << partition << "\"";
	return -1;
	}

	if (TEMP_FAILURE_RETRY(lseek(fd, start, SEEK_SET)) == -1) {
	PLOG(ERROR) << "Failed to seek to " << start << " on \"" << partition << "\"";
	return -1;
	}

	if (!android::base::WriteFully(fd, data + start, len - start)) {
	PLOG(ERROR) << "Failed to write " << len - start << " bytes to \"" << partition << "\"";
	return -1;
	}

	if (fsync(fd) != 0) {
	PLOG(ERROR) << "Failed to sync \"" << partition << "\"";
	return -1;
	}
	if (close(fd.release()) != 0) {
	PLOG(ERROR) << "Failed to close \"" << partition << "\"";
	return -1;
	}

	fd.reset(open(partition.c_str(), O_RDONLY));
	if (fd == -1) {
	PLOG(ERROR) << "Failed to reopen \"" << partition << "\" for verification";
	return -1;
	}

	// Drop caches so our subsequent verification read won't just be reading the cache.
	sync();
	std::string drop_cache = "/proc/sys/vm/drop_caches";
	if (!android::base::WriteStringToFile("3\n", drop_cache)) {
	PLOG(ERROR) << "Failed to write to " << drop_cache;
	} else {
	LOG(INFO) << " caches dropped";
	}
	sleep(1);

	// Verify.
	if (TEMP_FAILURE_RETRY(lseek(fd, 0, SEEK_SET)) == -1) {
	PLOG(ERROR) << "Failed to seek to 0 on " << partition;
	return -1;
	}

	unsigned char buffer[4096];
	start = len;
	for (size_t p = 0; p < len; p += sizeof(buffer)) {
	size_t to_read = len - p;
	if (to_read > sizeof(buffer)) {
	to_read = sizeof(buffer);
	}

	if (!android::base::ReadFully(fd, buffer, to_read)) {
	PLOG(ERROR) << "Failed to verify-read " << partition << " at " << p;
	return -1;
	}

	if (memcmp(buffer, data + p, to_read) != 0) {
	LOG(ERROR) << "Verification failed starting at " << p;
	start = p;
	break;
	}
	}

	if (start == len) {
	LOG(INFO) << "Verification read succeeded (attempt " << attempt + 1 << ")";
	success = true;
	break;
	}

	if (close(fd.release()) != 0) {
	PLOG(ERROR) << "Failed to close " << partition;
	return -1;
	}
	}

	if (!success) {
	LOG(ERROR) << "Failed to verify after all attempts";
	return -1;
	}

	sync();

	return 0;
	}

	int ParseSha1(const std::string& str, uint8_t* digest) {
	const char* ps = str.c_str();
	uint8_t* pd = digest;
	for (int i = 0; i < SHA_DIGEST_LENGTH * 2; ++i, ++ps) {
	int digit;
	if (ps >= '0' && ps <= '9') {
	digit = *ps - '0';
	} else if (ps >= 'a' && ps <= 'f') {
	digit = *ps - 'a' + 10;
	} else if (ps >= 'A' && ps <= 'F') {
	digit = *ps - 'A' + 10;
	} else {
	return -1;
	}
	if (i % 2 == 0) {
	*pd = digit << 4;
	} else {
	*pd \|= digit;
	++pd;
	}
	}
	if (*ps != '\0') return -1;
	return 0;
	}

	// Searches a vector of SHA-1 strings for one matching the given SHA-1. Returns the index of the
	// match on success, or -1 if no match is found.
	static int FindMatchingPatch(const uint8_t* sha1, const std::vector<std::string>& patch_sha1s) {
	for (size_t i = 0; i < patch_sha1s.size(); ++i) {
	uint8_t patch_sha1[SHA_DIGEST_LENGTH];
	if (ParseSha1(patch_sha1s[i], patch_sha1) == 0 &&
	memcmp(patch_sha1, sha1, SHA_DIGEST_LENGTH) == 0) {
	return i;
	}
	}
	return -1;
	}

	int applypatch_check(const std::string& filename, const std::vector<std::string>& sha1s) {
	if (!android::base::StartsWith(filename, "EMMC:")) {
	return 1;
	}

	// The check will pass if LoadPartitionContents is successful, because the filename already
	// encodes the desired SHA-1s.
	FileContents file;
	if (LoadPartitionContents(filename, &file) != 0) {
	LOG(INFO) << "\"" << filename << "\" doesn't have any of expected SHA-1 sums; checking cache";

	// If the partition is corrupted, it might be because we were killed in the middle of patching
	// it. A copy should have been made in cache_temp_source. If that file exists and matches the
	// SHA-1 we're looking for, the check still passes.
	if (LoadFileContents(Paths::Get().cache_temp_source(), &file) != 0) {
	LOG(ERROR) << "Failed to load cache file";
	return 1;
	}

	if (FindMatchingPatch(file.sha1, sha1s) < 0) {
	LOG(ERROR) << "The cache bits don't match any SHA-1 for \"" << filename << "\"";
	return 1;
	}
	}
	return 0;
	}

	int ShowLicenses() {
	ShowBSDiffLicense();
	return 0;
	}

	int applypatch(const char* source_filename, const char* target_filename,
	const char* target_sha1_str, size_t /* target_size */,
	const std::vector<std::string>& patch_sha1s,
	const std::vector<std::unique_ptr<Value>>& patch_data, const Value* bonus_data) {
	LOG(INFO) << "Patching " << source_filename;

	if (target_filename[0] == '-' && target_filename[1] == '\0') {
	target_filename = source_filename;
	}

	if (strncmp(target_filename, "EMMC:", 5) != 0) {
	LOG(ERROR) << "Supporting patching EMMC targets only";
	return 1;
	}

	uint8_t target_sha1[SHA_DIGEST_LENGTH];
	if (ParseSha1(target_sha1_str, target_sha1) != 0) {
	LOG(ERROR) << "Failed to parse target SHA-1 \"" << target_sha1_str << "\"";
	return 1;
	}

	// We try to load the target file into the source_file object.
	FileContents source_file;
	if (LoadFileContents(target_filename, &source_file) == 0) {
	if (memcmp(source_file.sha1, target_sha1, SHA_DIGEST_LENGTH) == 0) {
	// The early-exit case: the patch was already applied, this file has the desired hash, nothing
	// for us to do.
	LOG(INFO) << " already " << short_sha1(target_sha1);
	return 0;
	}
	}

	if (source_file.data.empty() \|\|
	(target_filename != source_filename && strcmp(target_filename, source_filename) != 0)) {
	// Need to load the source file: either we failed to load the target file, or we did but it's
	// different from the expected.
	source_file.data.clear();
	LoadFileContents(source_filename, &source_file);
	}

	if (!source_file.data.empty()) {
	int to_use = FindMatchingPatch(source_file.sha1, patch_sha1s);
	if (to_use != -1) {
	return GenerateTarget(source_file, patch_data[to_use], target_filename, target_sha1,
	bonus_data);
	}
	}

	LOG(INFO) << "Source file is bad; trying copy";

	FileContents copy_file;
	if (LoadFileContents(Paths::Get().cache_temp_source(), &copy_file) < 0) {
	LOG(ERROR) << "Failed to read copy file";
	return 1;
	}

	int to_use = FindMatchingPatch(copy_file.sha1, patch_sha1s);
	if (to_use == -1) {
	LOG(ERROR) << "The copy on /cache doesn't match source SHA-1s either";
	return 1;
	}

	return GenerateTarget(copy_file, patch_data[to_use], target_filename, target_sha1, bonus_data);
	}

	int applypatch_flash(const char* source_filename, const char* target_filename,
	const char* target_sha1_str, size_t target_size) {
	LOG(INFO) << "Flashing " << target_filename;

	uint8_t target_sha1[SHA_DIGEST_LENGTH];
	if (ParseSha1(target_sha1_str, target_sha1) != 0) {
	LOG(ERROR) << "Failed to parse target SHA-1 \"" << target_sha1_str << "\"";
	return 1;
	}

	std::vector<std::string> pieces = android::base::Split(target_filename, ":");
	if (pieces.size() != 4 \|\| pieces[0] != "EMMC") {
	LOG(ERROR) << "Invalid target name \"" << target_filename << "\"";
	return 1;
	}

	// Load the target into the source_file object to see if already applied.
	FileContents source_file;
	if (LoadPartitionContents(target_filename, &source_file) == 0 &&
	memcmp(source_file.sha1, target_sha1, SHA_DIGEST_LENGTH) == 0) {
	// The early-exit case: the image was already applied, this partition has the desired hash,
	// nothing for us to do.
	LOG(INFO) << " already " << short_sha1(target_sha1);
	return 0;
	}

	if (LoadFileContents(source_filename, &source_file) == 0) {
	if (memcmp(source_file.sha1, target_sha1, SHA_DIGEST_LENGTH) != 0) {
	// The source doesn't have desired checksum.
	LOG(ERROR) << "source \"" << source_filename << "\" doesn't have expected SHA-1 sum";
	LOG(ERROR) << "expected: " << short_sha1(target_sha1)
	<< ", found: " << short_sha1(source_file.sha1);
	return 1;
	}
	}

	if (WriteToPartition(source_file.data.data(), target_size, target_filename) != 0) {
	LOG(ERROR) << "Failed to write copied data to " << target_filename;
	return 1;
	}
	return 0;
	}

	static int GenerateTarget(const FileContents& source_file, const std::unique_ptr<Value>& patch,
	const std::string& target_filename,
	const uint8_t target_sha1[SHA_DIGEST_LENGTH], const Value* bonus_data) {
	if (patch->type != Value::Type::BLOB) {
	LOG(ERROR) << "patch is not a blob";
	return 1;
	}

	const char* header = &patch->data[0];
	size_t header_bytes_read = patch->data.size();
	bool use_bsdiff = false;
	if (header_bytes_read >= 8 && memcmp(header, "BSDIFF40", 8) == 0) {
	use_bsdiff = true;
	} else if (header_bytes_read >= 8 && memcmp(header, "IMGDIFF2", 8) == 0) {
	use_bsdiff = false;
	} else {
	LOG(ERROR) << "Unknown patch file format";
	return 1;
	}

	CHECK(android::base::StartsWith(target_filename, "EMMC:"));

	// We write the original source to cache, in case the partition write is interrupted.
	if (!CheckAndFreeSpaceOnCache(source_file.data.size())) {
	LOG(ERROR) << "Not enough free space on /cache";
	return 1;
	}
	if (SaveFileContents(Paths::Get().cache_temp_source(), &source_file) < 0) {
	LOG(ERROR) << "Failed to back up source file";
	return 1;
	}

	// We store the decoded output in memory.
	std::string memory_sink_str; // Don't need to reserve space.
	SHA_CTX ctx;
	SHA1_Init(&ctx);
	SinkFn sink = [&memory_sink_str, &ctx](const unsigned char* data, size_t len) {
	SHA1_Update(&ctx, data, len);
	memory_sink_str.append(reinterpret_cast<const char*>(data), len);
	return len;
	};

	int result;
	if (use_bsdiff) {
	result = ApplyBSDiffPatch(source_file.data.data(), source_file.data.size(), *patch, 0, sink);
	} else {
	result =
	ApplyImagePatch(source_file.data.data(), source_file.data.size(), *patch, sink, bonus_data);
	}

	if (result != 0) {
	LOG(ERROR) << "Failed to apply the patch: " << result;
	return 1;
	}

	uint8_t current_target_sha1[SHA_DIGEST_LENGTH];
	SHA1_Final(current_target_sha1, &ctx);
	if (memcmp(current_target_sha1, target_sha1, SHA_DIGEST_LENGTH) != 0) {
	LOG(ERROR) << "Patching did not produce the expected SHA-1 of " << short_sha1(target_sha1);

	LOG(ERROR) << "target size " << memory_sink_str.size() << " SHA-1 "
	<< short_sha1(current_target_sha1);
	LOG(ERROR) << "source size " << source_file.data.size() << " SHA-1 "
	<< short_sha1(source_file.sha1);

	uint8_t patch_digest[SHA_DIGEST_LENGTH];
	SHA1(reinterpret_cast<const uint8_t*>(patch->data.data()), patch->data.size(), patch_digest);
	LOG(ERROR) << "patch size " << patch->data.size() << " SHA-1 " << short_sha1(patch_digest);

	if (bonus_data != nullptr) {
	uint8_t bonus_digest[SHA_DIGEST_LENGTH];
	SHA1(reinterpret_cast<const uint8_t*>(bonus_data->data.data()), bonus_data->data.size(),
	bonus_digest);
	LOG(ERROR) << "bonus size " << bonus_data->data.size() << " SHA-1 "
	<< short_sha1(bonus_digest);
	}

	return 1;
	} else {
	LOG(INFO) << " now " << short_sha1(target_sha1);
	}

	// Write back the temp file to the partition.
	if (WriteToPartition(reinterpret_cast<const unsigned char*>(memory_sink_str.c_str()),
	memory_sink_str.size(), target_filename) != 0) {
	LOG(ERROR) << "Failed to write patched data to " << target_filename;
	return 1;
	}

	// Delete the backup copy of the source.
	unlink(Paths::Get().cache_temp_source().c_str());

	// Success!
	return 0;
	}