1 // Copyright (c) 2011 The LevelDB Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. See the AUTHORS file for names of contributors. 4 5 #ifndef STORAGE_LEVELDB_DB_LOG_READER_H_ 6 #define STORAGE_LEVELDB_DB_LOG_READER_H_ 7 8 #include <stdint.h> 9 10 #include "db/log_format.h" 11 #include "leveldb/slice.h" 12 #include "leveldb/status.h" 13 14 namespace leveldb { 15 16 class SequentialFile; 17 18 namespace log { 19 20 class Reader { 21 public: 22 // Interface for reporting errors. 23 class Reporter { 24 public: 25 virtual ~Reporter(); 26 27 // Some corruption was detected. "size" is the approximate number 28 // of bytes dropped due to the corruption. 29 virtual void Corruption(size_t bytes, const Status& status) = 0; 30 }; 31 32 // Create a reader that will return log records from "*file". 33 // "*file" must remain live while this Reader is in use. 34 // 35 // If "reporter" is non-NULL, it is notified whenever some data is 36 // dropped due to a detected corruption. "*reporter" must remain 37 // live while this Reader is in use. 38 // 39 // If "checksum" is true, verify checksums if available. 40 // 41 // The Reader will start reading at the first record located at physical 42 // position >= initial_offset within the file. 43 Reader(SequentialFile* file, Reporter* reporter, bool checksum, 44 uint64_t initial_offset); 45 46 ~Reader(); 47 48 // Read the next record into *record. Returns true if read 49 // successfully, false if we hit end of the input. May use 50 // "*scratch" as temporary storage. The contents filled in *record 51 // will only be valid until the next mutating operation on this 52 // reader or the next mutation to *scratch. 53 bool ReadRecord(Slice* record, std::string* scratch); 54 55 // Returns the physical offset of the last record returned by ReadRecord. 56 // 57 // Undefined before the first call to ReadRecord. 58 uint64_t LastRecordOffset(); 59 60 private: 61 SequentialFile* const file_; 62 Reporter* const reporter_; 63 bool const checksum_; 64 char* const backing_store_; 65 Slice buffer_; 66 bool eof_; // Last Read() indicated EOF by returning < kBlockSize 67 68 // Offset of the last record returned by ReadRecord. 69 uint64_t last_record_offset_; 70 // Offset of the first location past the end of buffer_. 71 uint64_t end_of_buffer_offset_; 72 73 // Offset at which to start looking for the first record to return 74 uint64_t const initial_offset_; 75 76 // Extend record types with the following special values 77 enum { 78 kEof = kMaxRecordType + 1, 79 // Returned whenever we find an invalid physical record. 80 // Currently there are three situations in which this happens: 81 // * The record has an invalid CRC (ReadPhysicalRecord reports a drop) 82 // * The record is a 0-length record (No drop is reported) 83 // * The record is below constructor's initial_offset (No drop is reported) 84 kBadRecord = kMaxRecordType + 2 85 }; 86 87 // Skips all blocks that are completely before "initial_offset_". 88 // 89 // Returns true on success. Handles reporting. 90 bool SkipToInitialBlock(); 91 92 // Return type, or one of the preceding special values 93 unsigned int ReadPhysicalRecord(Slice* result); 94 95 // Reports dropped bytes to the reporter. 96 // buffer_ must be updated to remove the dropped bytes prior to invocation. 97 void ReportCorruption(size_t bytes, const char* reason); 98 void ReportDrop(size_t bytes, const Status& reason); 99 100 // No copying allowed 101 Reader(const Reader&); 102 void operator=(const Reader&); 103 }; 104 105 } // namespace log 106 } // namespace leveldb 107 108 #endif // STORAGE_LEVELDB_DB_LOG_READER_H_ 109
