github.com/cellofellow/gopkg@v0.0.0-20140722061823-eec0544a62ad/database/leveldb.chai2010/include/db/log_reader.h (about)

     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_