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_TABLE_FORMAT_H_ |
6 | #define STORAGE_LEVELDB_TABLE_FORMAT_H_ |
7 | |
8 | #include <cstdint> |
9 | #include <string> |
10 | |
11 | #include "leveldb/slice.h" |
12 | #include "leveldb/status.h" |
13 | #include "leveldb/table_builder.h" |
14 | |
15 | namespace leveldb { |
16 | |
17 | class Block; |
18 | class RandomAccessFile; |
19 | struct ReadOptions; |
20 | |
21 | // BlockHandle is a pointer to the extent of a file that stores a data |
22 | // block or a meta block. |
23 | class BlockHandle { |
24 | public: |
25 | // Maximum encoding length of a BlockHandle |
26 | enum { kMaxEncodedLength = 10 + 10 }; |
27 | |
28 | BlockHandle(); |
29 | |
30 | // The offset of the block in the file. |
31 | uint64_t offset() const { return offset_; } |
32 | void set_offset(uint64_t offset) { offset_ = offset; } |
33 | |
34 | // The size of the stored block |
35 | uint64_t size() const { return size_; } |
36 | void set_size(uint64_t size) { size_ = size; } |
37 | |
38 | void EncodeTo(std::string* dst) const; |
39 | Status DecodeFrom(Slice* input); |
40 | |
41 | private: |
42 | uint64_t offset_; |
43 | uint64_t size_; |
44 | }; |
45 | |
46 | // Footer encapsulates the fixed information stored at the tail |
47 | // end of every table file. |
48 | class { |
49 | public: |
50 | // Encoded length of a Footer. Note that the serialization of a |
51 | // Footer will always occupy exactly this many bytes. It consists |
52 | // of two block handles and a magic number. |
53 | enum { = 2 * BlockHandle::kMaxEncodedLength + 8 }; |
54 | |
55 | () = default; |
56 | |
57 | // The block handle for the metaindex block of the table |
58 | const BlockHandle& metaindex_handle() const { return metaindex_handle_; } |
59 | void set_metaindex_handle(const BlockHandle& h) { metaindex_handle_ = h; } |
60 | |
61 | // The block handle for the index block of the table |
62 | const BlockHandle& index_handle() const { return index_handle_; } |
63 | void set_index_handle(const BlockHandle& h) { index_handle_ = h; } |
64 | |
65 | void (std::string* dst) const; |
66 | Status (Slice* input); |
67 | |
68 | private: |
69 | BlockHandle metaindex_handle_; |
70 | BlockHandle index_handle_; |
71 | }; |
72 | |
73 | // kTableMagicNumber was picked by running |
74 | // echo http://code.google.com/p/leveldb/ | sha1sum |
75 | // and taking the leading 64 bits. |
76 | static const uint64_t kTableMagicNumber = 0xdb4775248b80fb57ull; |
77 | |
78 | // 1-byte type + 32-bit crc |
79 | static const size_t kBlockTrailerSize = 5; |
80 | |
81 | struct BlockContents { |
82 | Slice data; // Actual contents of data |
83 | bool cachable; // True iff data can be cached |
84 | bool heap_allocated; // True iff caller should delete[] data.data() |
85 | }; |
86 | |
87 | // Read the block identified by "handle" from "file". On failure |
88 | // return non-OK. On success fill *result and return OK. |
89 | Status ReadBlock(RandomAccessFile* file, const ReadOptions& options, |
90 | const BlockHandle& handle, BlockContents* result); |
91 | |
92 | // Implementation details follow. Clients should ignore, |
93 | |
94 | inline BlockHandle::BlockHandle() |
95 | : offset_(~static_cast<uint64_t>(0)), size_(~static_cast<uint64_t>(0)) {} |
96 | |
97 | } // namespace leveldb |
98 | |
99 | #endif // STORAGE_LEVELDB_TABLE_FORMAT_H_ |
100 | |