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112 linhas
3.7 KiB
112 linhas
3.7 KiB
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file. See the AUTHORS file for names of contributors.
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#ifndef STORAGE_LEVELDB_DB_LOG_READER_H_
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#define STORAGE_LEVELDB_DB_LOG_READER_H_
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#include <cstdint>
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#include "db/log_format.h"
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#include "leveldb/slice.h"
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#include "leveldb/status.h"
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namespace leveldb {
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class SequentialFile;
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namespace log {
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class Reader {
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public:
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// Interface for reporting errors.
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class Reporter {
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public:
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virtual ~Reporter();
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// Some corruption was detected. "size" is the approximate number
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// of bytes dropped due to the corruption.
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virtual void Corruption(size_t bytes, const Status& status) = 0;
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};
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// Create a reader that will return log records from "*file".
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// "*file" must remain live while this Reader is in use.
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//
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// If "reporter" is non-null, it is notified whenever some data is
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// dropped due to a detected corruption. "*reporter" must remain
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// live while this Reader is in use.
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//
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// If "checksum" is true, verify checksums if available.
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//
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// The Reader will start reading at the first record located at physical
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// position >= initial_offset within the file.
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Reader(SequentialFile* file, Reporter* reporter, bool checksum,
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uint64_t initial_offset);
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Reader(const Reader&) = delete;
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Reader& operator=(const Reader&) = delete;
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~Reader();
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// Read the next record into *record. Returns true if read
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// successfully, false if we hit end of the input. May use
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// "*scratch" as temporary storage. The contents filled in *record
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// will only be valid until the next mutating operation on this
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// reader or the next mutation to *scratch.
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bool ReadRecord(Slice* record, std::string* scratch);
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// Returns the physical offset of the last record returned by ReadRecord.
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//
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// Undefined before the first call to ReadRecord.
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uint64_t LastRecordOffset();
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private:
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// Extend record types with the following special values
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enum {
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kEof = kMaxRecordType + 1,
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// Returned whenever we find an invalid physical record.
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// Currently there are three situations in which this happens:
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// * The record has an invalid CRC (ReadPhysicalRecord reports a drop)
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// * The record is a 0-length record (No drop is reported)
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// * The record is below constructor's initial_offset (No drop is reported)
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kBadRecord = kMaxRecordType + 2
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};
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// Skips all blocks that are completely before "initial_offset_".
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//
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// Returns true on success. Handles reporting.
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bool SkipToInitialBlock();
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// Return type, or one of the preceding special values
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unsigned int ReadPhysicalRecord(Slice* result);
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// Reports dropped bytes to the reporter.
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// buffer_ must be updated to remove the dropped bytes prior to invocation.
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void ReportCorruption(uint64_t bytes, const char* reason);
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void ReportDrop(uint64_t bytes, const Status& reason);
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SequentialFile* const file_;
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Reporter* const reporter_;
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bool const checksum_;
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char* const backing_store_;
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Slice buffer_;
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bool eof_; // Last Read() indicated EOF by returning < kBlockSize
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// Offset of the last record returned by ReadRecord.
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uint64_t last_record_offset_;
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// Offset of the first location past the end of buffer_.
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uint64_t end_of_buffer_offset_;
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// Offset at which to start looking for the first record to return
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uint64_t const initial_offset_;
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// True if we are resynchronizing after a seek (initial_offset_ > 0). In
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// particular, a run of kMiddleType and kLastType records can be silently
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// skipped in this mode
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bool resyncing_;
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};
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} // namespace log
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} // namespace leveldb
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#endif // STORAGE_LEVELDB_DB_LOG_READER_H_
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