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       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         [ +  + ]:        4609 :   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(const Reader&) = delete;
      47                 :             :   Reader& operator=(const Reader&) = delete;
      48                 :             : 
      49                 :             :   ~Reader();
      50                 :             : 
      51                 :             :   // Read the next record into *record.  Returns true if read
      52                 :             :   // successfully, false if we hit end of the input.  May use
      53                 :             :   // "*scratch" as temporary storage.  The contents filled in *record
      54                 :             :   // will only be valid until the next mutating operation on this
      55                 :             :   // reader or the next mutation to *scratch.
      56                 :             :   bool ReadRecord(Slice* record, std::string* scratch);
      57                 :             : 
      58                 :             :   // Returns the physical offset of the last record returned by ReadRecord.
      59                 :             :   //
      60                 :             :   // Undefined before the first call to ReadRecord.
      61                 :             :   uint64_t LastRecordOffset();
      62                 :             : 
      63                 :             :  private:
      64                 :             :   // Extend record types with the following special values
      65                 :             :   enum {
      66                 :             :     kEof = kMaxRecordType + 1,
      67                 :             :     // Returned whenever we find an invalid physical record.
      68                 :             :     // Currently there are three situations in which this happens:
      69                 :             :     // * The record has an invalid CRC (ReadPhysicalRecord reports a drop)
      70                 :             :     // * The record is a 0-length record (No drop is reported)
      71                 :             :     // * The record is below constructor's initial_offset (No drop is reported)
      72                 :             :     kBadRecord = kMaxRecordType + 2
      73                 :             :   };
      74                 :             : 
      75                 :             :   // Skips all blocks that are completely before "initial_offset_".
      76                 :             :   //
      77                 :             :   // Returns true on success. Handles reporting.
      78                 :             :   bool SkipToInitialBlock();
      79                 :             : 
      80                 :             :   // Return type, or one of the preceding special values
      81                 :             :   unsigned int ReadPhysicalRecord(Slice* result);
      82                 :             : 
      83                 :             :   // Reports dropped bytes to the reporter.
      84                 :             :   // buffer_ must be updated to remove the dropped bytes prior to invocation.
      85                 :             :   void ReportCorruption(uint64_t bytes, const char* reason);
      86                 :             :   void ReportDrop(uint64_t bytes, const Status& reason);
      87                 :             : 
      88                 :             :   SequentialFile* const file_;
      89                 :             :   Reporter* const reporter_;
      90                 :             :   bool const checksum_;
      91                 :             :   char* const backing_store_;
      92                 :             :   Slice buffer_;
      93                 :             :   bool eof_;  // Last Read() indicated EOF by returning < kBlockSize
      94                 :             : 
      95                 :             :   // Offset of the last record returned by ReadRecord.
      96                 :             :   uint64_t last_record_offset_;
      97                 :             :   // Offset of the first location past the end of buffer_.
      98                 :             :   uint64_t end_of_buffer_offset_;
      99                 :             : 
     100                 :             :   // Offset at which to start looking for the first record to return
     101                 :             :   uint64_t const initial_offset_;
     102                 :             : 
     103                 :             :   // True if we are resynchronizing after a seek (initial_offset_ > 0). In
     104                 :             :   // particular, a run of kMiddleType and kLastType records can be silently
     105                 :             :   // skipped in this mode
     106                 :             :   bool resyncing_;
     107                 :             : };
     108                 :             : 
     109                 :             : }  // namespace log
     110                 :             : }  // namespace leveldb
     111                 :             : 
     112                 :             : #endif  // STORAGE_LEVELDB_DB_LOG_READER_H_