text: // Copyright (c) 2011 The LevelDB Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file. See the AUTHORS file for names of contributors.
  
  #ifndef STORAGE_LEVELDB_TABLE_BLOCK_BUILDER_H_
  #define STORAGE_LEVELDB_TABLE_BLOCK_BUILDER_H_
  
  #include <cstdint>
  #include <vector>
  
  #include "leveldb/slice.h"
  
  namespace leveldb {
  
  struct Options;
  
  // 用于 block 的写入
  class BlockBuilder {
   public:
    explicit BlockBuilder(const Options* options);
  
    BlockBuilder(const BlockBuilder&) = delete;
    BlockBuilder& operator=(const BlockBuilder&) = delete;
  
    // Reset the contents as if the BlockBuilder was just constructed.
    void Reset();
  
    // REQUIRES: Finish() has not been called since the last call to Reset().
    // REQUIRES: key is larger than any previously added key
    void Add(const Slice& key, const Slice& value);
  
    // Finish building the block and return a slice that refers to the
    // block contents.  The returned slice will remain valid for the
    // lifetime of this builder or until Reset() is called.
    Slice Finish();
  
    // Returns an estimate of the current (uncompressed) size of the block
    // we are building.
    size_t CurrentSizeEstimate() const;
  
    // Return true iff no entries have been added since the last Reset()
    bool empty() const { return buffer_.empty(); }
  
   private:
    const Options* options_;
    std::string buffer_;              // Destination buffer
    std::vector<uint32_t> restarts_;  // Restart points
    int counter_;                     // Number of entries emitted since restart
    bool finished_;                   // Has Finish() been called?
    std::string last_key_;
  };
  
  }  // namespace leveldb
  
  #endif  // STORAGE_LEVELDB_TABLE_BLOCK_BUILDER_H_
  