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-rw-r--r--src/leveldb/db/log_reader.cc259
1 files changed, 259 insertions, 0 deletions
diff --git a/src/leveldb/db/log_reader.cc b/src/leveldb/db/log_reader.cc
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+++ b/src/leveldb/db/log_reader.cc
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+// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file. See the AUTHORS file for names of contributors.
+
+#include "db/log_reader.h"
+
+#include <stdio.h>
+#include "leveldb/env.h"
+#include "util/coding.h"
+#include "util/crc32c.h"
+
+namespace leveldb {
+namespace log {
+
+Reader::Reporter::~Reporter() {
+}
+
+Reader::Reader(SequentialFile* file, Reporter* reporter, bool checksum,
+ uint64_t initial_offset)
+ : file_(file),
+ reporter_(reporter),
+ checksum_(checksum),
+ backing_store_(new char[kBlockSize]),
+ buffer_(),
+ eof_(false),
+ last_record_offset_(0),
+ end_of_buffer_offset_(0),
+ initial_offset_(initial_offset) {
+}
+
+Reader::~Reader() {
+ delete[] backing_store_;
+}
+
+bool Reader::SkipToInitialBlock() {
+ size_t offset_in_block = initial_offset_ % kBlockSize;
+ uint64_t block_start_location = initial_offset_ - offset_in_block;
+
+ // Don't search a block if we'd be in the trailer
+ if (offset_in_block > kBlockSize - 6) {
+ offset_in_block = 0;
+ block_start_location += kBlockSize;
+ }
+
+ end_of_buffer_offset_ = block_start_location;
+
+ // Skip to start of first block that can contain the initial record
+ if (block_start_location > 0) {
+ Status skip_status = file_->Skip(block_start_location);
+ if (!skip_status.ok()) {
+ ReportDrop(block_start_location, skip_status);
+ return false;
+ }
+ }
+
+ return true;
+}
+
+bool Reader::ReadRecord(Slice* record, std::string* scratch) {
+ if (last_record_offset_ < initial_offset_) {
+ if (!SkipToInitialBlock()) {
+ return false;
+ }
+ }
+
+ scratch->clear();
+ record->clear();
+ bool in_fragmented_record = false;
+ // Record offset of the logical record that we're reading
+ // 0 is a dummy value to make compilers happy
+ uint64_t prospective_record_offset = 0;
+
+ Slice fragment;
+ while (true) {
+ uint64_t physical_record_offset = end_of_buffer_offset_ - buffer_.size();
+ const unsigned int record_type = ReadPhysicalRecord(&fragment);
+ switch (record_type) {
+ case kFullType:
+ if (in_fragmented_record) {
+ // Handle bug in earlier versions of log::Writer where
+ // it could emit an empty kFirstType record at the tail end
+ // of a block followed by a kFullType or kFirstType record
+ // at the beginning of the next block.
+ if (scratch->empty()) {
+ in_fragmented_record = false;
+ } else {
+ ReportCorruption(scratch->size(), "partial record without end(1)");
+ }
+ }
+ prospective_record_offset = physical_record_offset;
+ scratch->clear();
+ *record = fragment;
+ last_record_offset_ = prospective_record_offset;
+ return true;
+
+ case kFirstType:
+ if (in_fragmented_record) {
+ // Handle bug in earlier versions of log::Writer where
+ // it could emit an empty kFirstType record at the tail end
+ // of a block followed by a kFullType or kFirstType record
+ // at the beginning of the next block.
+ if (scratch->empty()) {
+ in_fragmented_record = false;
+ } else {
+ ReportCorruption(scratch->size(), "partial record without end(2)");
+ }
+ }
+ prospective_record_offset = physical_record_offset;
+ scratch->assign(fragment.data(), fragment.size());
+ in_fragmented_record = true;
+ break;
+
+ case kMiddleType:
+ if (!in_fragmented_record) {
+ ReportCorruption(fragment.size(),
+ "missing start of fragmented record(1)");
+ } else {
+ scratch->append(fragment.data(), fragment.size());
+ }
+ break;
+
+ case kLastType:
+ if (!in_fragmented_record) {
+ ReportCorruption(fragment.size(),
+ "missing start of fragmented record(2)");
+ } else {
+ scratch->append(fragment.data(), fragment.size());
+ *record = Slice(*scratch);
+ last_record_offset_ = prospective_record_offset;
+ return true;
+ }
+ break;
+
+ case kEof:
+ if (in_fragmented_record) {
+ ReportCorruption(scratch->size(), "partial record without end(3)");
+ scratch->clear();
+ }
+ return false;
+
+ case kBadRecord:
+ if (in_fragmented_record) {
+ ReportCorruption(scratch->size(), "error in middle of record");
+ in_fragmented_record = false;
+ scratch->clear();
+ }
+ break;
+
+ default: {
+ char buf[40];
+ snprintf(buf, sizeof(buf), "unknown record type %u", record_type);
+ ReportCorruption(
+ (fragment.size() + (in_fragmented_record ? scratch->size() : 0)),
+ buf);
+ in_fragmented_record = false;
+ scratch->clear();
+ break;
+ }
+ }
+ }
+ return false;
+}
+
+uint64_t Reader::LastRecordOffset() {
+ return last_record_offset_;
+}
+
+void Reader::ReportCorruption(size_t bytes, const char* reason) {
+ ReportDrop(bytes, Status::Corruption(reason));
+}
+
+void Reader::ReportDrop(size_t bytes, const Status& reason) {
+ if (reporter_ != NULL &&
+ end_of_buffer_offset_ - buffer_.size() - bytes >= initial_offset_) {
+ reporter_->Corruption(bytes, reason);
+ }
+}
+
+unsigned int Reader::ReadPhysicalRecord(Slice* result) {
+ while (true) {
+ if (buffer_.size() < kHeaderSize) {
+ if (!eof_) {
+ // Last read was a full read, so this is a trailer to skip
+ buffer_.clear();
+ Status status = file_->Read(kBlockSize, &buffer_, backing_store_);
+ end_of_buffer_offset_ += buffer_.size();
+ if (!status.ok()) {
+ buffer_.clear();
+ ReportDrop(kBlockSize, status);
+ eof_ = true;
+ return kEof;
+ } else if (buffer_.size() < kBlockSize) {
+ eof_ = true;
+ }
+ continue;
+ } else if (buffer_.size() == 0) {
+ // End of file
+ return kEof;
+ } else {
+ size_t drop_size = buffer_.size();
+ buffer_.clear();
+ ReportCorruption(drop_size, "truncated record at end of file");
+ return kEof;
+ }
+ }
+
+ // Parse the header
+ const char* header = buffer_.data();
+ const uint32_t a = static_cast<uint32_t>(header[4]) & 0xff;
+ const uint32_t b = static_cast<uint32_t>(header[5]) & 0xff;
+ const unsigned int type = header[6];
+ const uint32_t length = a | (b << 8);
+ if (kHeaderSize + length > buffer_.size()) {
+ size_t drop_size = buffer_.size();
+ buffer_.clear();
+ ReportCorruption(drop_size, "bad record length");
+ return kBadRecord;
+ }
+
+ if (type == kZeroType && length == 0) {
+ // Skip zero length record without reporting any drops since
+ // such records are produced by the mmap based writing code in
+ // env_posix.cc that preallocates file regions.
+ buffer_.clear();
+ return kBadRecord;
+ }
+
+ // Check crc
+ if (checksum_) {
+ uint32_t expected_crc = crc32c::Unmask(DecodeFixed32(header));
+ uint32_t actual_crc = crc32c::Value(header + 6, 1 + length);
+ if (actual_crc != expected_crc) {
+ // Drop the rest of the buffer since "length" itself may have
+ // been corrupted and if we trust it, we could find some
+ // fragment of a real log record that just happens to look
+ // like a valid log record.
+ size_t drop_size = buffer_.size();
+ buffer_.clear();
+ ReportCorruption(drop_size, "checksum mismatch");
+ return kBadRecord;
+ }
+ }
+
+ buffer_.remove_prefix(kHeaderSize + length);
+
+ // Skip physical record that started before initial_offset_
+ if (end_of_buffer_offset_ - buffer_.size() - kHeaderSize - length <
+ initial_offset_) {
+ result->clear();
+ return kBadRecord;
+ }
+
+ *result = Slice(header + kHeaderSize, length);
+ return type;
+ }
+}
+
+} // namespace log
+} // namespace leveldb