ceph/src/rocksdb/utilities/blob_db/blob_log_reader.h

   1 //  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
   2 //  This source code is licensed under both the GPLv2 (found in the
   3 //  COPYING file in the root directory) and Apache 2.0 License
   4 //  (found in the LICENSE.Apache file in the root directory).
   5 //
   6 #pragma once
   7
   8 #ifndef ROCKSDB_LITE
   9
  10 #include <memory>
  11 #include <string>
  12
  13 #include "file/random_access_file_reader.h"
  14 #include "rocksdb/env.h"
  15 #include "rocksdb/slice.h"
  16 #include "rocksdb/statistics.h"
  17 #include "rocksdb/status.h"
  18 #include "utilities/blob_db/blob_log_format.h"
  19
  20 namespace ROCKSDB_NAMESPACE {
  21
  22 class SequentialFileReader;
  23 class Logger;
  24
  25 namespace blob_db {
  26
  27 /**
  28  * Reader is a general purpose log stream reader implementation. The actual job
  29  * of reading from the device is implemented by the SequentialFile interface.
  30  *
  31  * Please see Writer for details on the file and record layout.
  32  */
  33 class Reader {
  34  public:
  35   enum ReadLevel {
  36     kReadHeader,
  37     kReadHeaderKey,
  38     kReadHeaderKeyBlob,
  39   };
  40
  41   // Create a reader that will return log records from "*file".
  42   // "*file" must remain live while this Reader is in use.
  43   Reader(std::unique_ptr<RandomAccessFileReader>&& file_reader, Env* env,
  44          Statistics* statistics);
  45   // No copying allowed
  46   Reader(const Reader&) = delete;
  47   Reader& operator=(const Reader&) = delete;
  48
  49   ~Reader() = default;
  50
  51   Status ReadHeader(BlobLogHeader* header);
  52
  53   // Read the next record into *record.  Returns true if read
  54   // successfully, false if we hit end of the input.  May use
  55   // "*scratch" as temporary storage.  The contents filled in *record
  56   // will only be valid until the next mutating operation on this
  57   // reader or the next mutation to *scratch.
  58   // If blob_offset is non-null, return offset of the blob through it.
  59   Status ReadRecord(BlobLogRecord* record, ReadLevel level = kReadHeader,
  60                     uint64_t* blob_offset = nullptr);
  61
  62   void ResetNextByte() { next_byte_ = 0; }
  63
  64   uint64_t GetNextByte() const { return next_byte_; }
  65
  66  private:
  67   Status ReadSlice(uint64_t size, Slice* slice, char* buf);
  68
  69   const std::unique_ptr<RandomAccessFileReader> file_;
  70   Env* env_;
  71   Statistics* statistics_;
  72
  73   Slice buffer_;
  74   char header_buf_[BlobLogRecord::kHeaderSize];
  75
  76   // which byte to read next. For asserting proper usage
  77   uint64_t next_byte_;
  78 };
  79
  80 }  // namespace blob_db
  81 }  // namespace ROCKSDB_NAMESPACE
  82 #endif  // ROCKSDB_LITE