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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.
+
+#ifndef STORAGE_LEVELDB_DB_LOG_READER_H_
+#define STORAGE_LEVELDB_DB_LOG_READER_H_
+
+#include <stdint.h>
+
+#include "db/log_format.h"
+#include "leveldb/slice.h"
+#include "leveldb/status.h"
+
+namespace leveldb {
+
+class SequentialFile;
+
+namespace log {
+
+class Reader {
+ public:
+ // Interface for reporting errors.
+ class Reporter {
+ public:
+ virtual ~Reporter();
+
+ // Some corruption was detected. "size" is the approximate number
+ // of bytes dropped due to the corruption.
+ virtual void Corruption(size_t bytes, const Status& status) = 0;
+ };
+
+ // Create a reader that will return log records from "*file".
+ // "*file" must remain live while this Reader is in use.
+ //
+ // If "reporter" is non-NULL, it is notified whenever some data is
+ // dropped due to a detected corruption. "*reporter" must remain
+ // live while this Reader is in use.
+ //
+ // If "checksum" is true, verify checksums if available.
+ //
+ // The Reader will start reading at the first record located at physical
+ // position >= initial_offset within the file.
+ Reader(SequentialFile* file, Reporter* reporter, bool checksum,
+ uint64_t initial_offset);
+
+ ~Reader();
+
+ // Read the next record into *record. Returns true if read
+ // successfully, false if we hit end of the input. May use
+ // "*scratch" as temporary storage. The contents filled in *record
+ // will only be valid until the next mutating operation on this
+ // reader or the next mutation to *scratch.
+ bool ReadRecord(Slice* record, std::string* scratch);
+
+ // Returns the physical offset of the last record returned by ReadRecord.
+ //
+ // Undefined before the first call to ReadRecord.
+ uint64_t LastRecordOffset();
+
+ private:
+ SequentialFile* const file_;
+ Reporter* const reporter_;
+ bool const checksum_;
+ char* const backing_store_;
+ Slice buffer_;
+ bool eof_; // Last Read() indicated EOF by returning < kBlockSize
+
+ // Offset of the last record returned by ReadRecord.
+ uint64_t last_record_offset_;
+ // Offset of the first location past the end of buffer_.
+ uint64_t end_of_buffer_offset_;
+
+ // Offset at which to start looking for the first record to return
+ uint64_t const initial_offset_;
+
+ // Extend record types with the following special values
+ enum {
+ kEof = kMaxRecordType + 1,
+ // Returned whenever we find an invalid physical record.
+ // Currently there are three situations in which this happens:
+ // * The record has an invalid CRC (ReadPhysicalRecord reports a drop)
+ // * The record is a 0-length record (No drop is reported)
+ // * The record is below constructor's initial_offset (No drop is reported)
+ kBadRecord = kMaxRecordType + 2
+ };
+
+ // Skips all blocks that are completely before "initial_offset_".
+ //
+ // Returns true on success. Handles reporting.
+ bool SkipToInitialBlock();
+
+ // Return type, or one of the preceding special values
+ unsigned int ReadPhysicalRecord(Slice* result);
+
+ // Reports dropped bytes to the reporter.
+ // buffer_ must be updated to remove the dropped bytes prior to invocation.
+ void ReportCorruption(uint64_t bytes, const char* reason);
+ void ReportDrop(uint64_t bytes, const Status& reason);
+
+ // No copying allowed
+ Reader(const Reader&);
+ void operator=(const Reader&);
+};
+
+} // namespace log
+} // namespace leveldb
+
+#endif // STORAGE_LEVELDB_DB_LOG_READER_H_