| // Copyright (c) 2012 The Chromium Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| // |
| // A read-only set implementation for |SBPrefix| items. Prefixes are |
| // sorted and stored as 16-bit deltas from the previous prefix. An |
| // index structure provides quick random access, and also handles |
| // cases where 16 bits cannot encode a delta. |
| // |
| // For example, the sequence {20, 25, 41, 65432, 150000, 160000} would |
| // be stored as: |
| // A pair {20, 0} in |index_|. |
| // 5, 16, 65391 in |deltas_|. |
| // A pair {150000, 3} in |index_|. |
| // 10000 in |deltas_|. |
| // |index_.size()| will be 2, |deltas_.size()| will be 4. |
| // |
| // This structure is intended for storage of sparse uniform sets of |
| // prefixes of a certain size. As of this writing, my safe-browsing |
| // database contains: |
| // 653132 add prefixes |
| // 6446 are duplicates (from different chunks) |
| // 24301 w/in 2^8 of the prior prefix |
| // 622337 w/in 2^16 of the prior prefix |
| // 47 further than 2^16 from the prior prefix |
| // For this input, the memory usage is approximately 2 bytes per |
| // prefix, a bit over 1.2M. The bloom filter used 25 bits per prefix, |
| // a bit over 1.9M on this data. |
| // |
| // Experimenting with random selections of the above data, storage |
| // size drops almost linearly as prefix count drops, until the index |
| // overhead starts to become a problem a bit under 200k prefixes. The |
| // memory footprint gets worse than storing the raw prefix data around |
| // 75k prefixes. Fortunately, the actual memory footprint also falls. |
| // If the prefix count increases the memory footprint should increase |
| // approximately linearly. The worst-case would be 2^16 items all |
| // 2^16 apart, which would need 512k (versus 256k to store the raw |
| // data). |
| // |
| // The on-disk format looks like: |
| // 4 byte magic number |
| // 4 byte version number |
| // 4 byte |index_.size()| |
| // 4 byte |deltas_.size()| |
| // n * 8 byte |&index_[0]..&index_[n]| |
| // m * 2 byte |&deltas_[0]..&deltas_[m]| |
| // 16 byte digest |
| |
| #ifndef COMPONENTS_SAFE_BROWSING_DB_PREFIX_SET_H_ |
| #define COMPONENTS_SAFE_BROWSING_DB_PREFIX_SET_H_ |
| |
| #include <stddef.h> |
| #include <stdint.h> |
| |
| #include <utility> |
| #include <vector> |
| |
| #include "base/gtest_prod_util.h" |
| #include "base/macros.h" |
| #include "base/memory/scoped_ptr.h" |
| #include "components/safe_browsing_db/util.h" |
| |
| namespace base { |
| class FilePath; |
| } |
| |
| namespace safe_browsing { |
| |
| class PrefixSet { |
| public: |
| ~PrefixSet(); |
| |
| // |true| if |hash| is in the hashes passed to the set's builder, or if |
| // |hash.prefix| is one of the prefixes passed to the set's builder. |
| bool Exists(const SBFullHash& hash) const; |
| |
| // Persist the set on disk. |
| static scoped_ptr<const PrefixSet> LoadFile( |
| const base::FilePath& filter_name); |
| bool WriteFile(const base::FilePath& filter_name) const; |
| |
| private: |
| friend class PrefixSetBuilder; |
| |
| friend class PrefixSetTest; |
| FRIEND_TEST_ALL_PREFIXES(PrefixSetTest, AllBig); |
| FRIEND_TEST_ALL_PREFIXES(PrefixSetTest, EdgeCases); |
| FRIEND_TEST_ALL_PREFIXES(PrefixSetTest, Empty); |
| FRIEND_TEST_ALL_PREFIXES(PrefixSetTest, FullHashBuild); |
| FRIEND_TEST_ALL_PREFIXES(PrefixSetTest, IntMinMax); |
| FRIEND_TEST_ALL_PREFIXES(PrefixSetTest, OneElement); |
| FRIEND_TEST_ALL_PREFIXES(PrefixSetTest, ReadWrite); |
| FRIEND_TEST_ALL_PREFIXES(PrefixSetTest, ReadWriteSigned); |
| FRIEND_TEST_ALL_PREFIXES(PrefixSetTest, Version3); |
| |
| FRIEND_TEST_ALL_PREFIXES(SafeBrowsingStoreFileTest, BasicStore); |
| FRIEND_TEST_ALL_PREFIXES(SafeBrowsingStoreFileTest, DeleteChunks); |
| FRIEND_TEST_ALL_PREFIXES(SafeBrowsingStoreFileTest, DetectsCorruption); |
| FRIEND_TEST_ALL_PREFIXES(SafeBrowsingStoreFileTest, Empty); |
| FRIEND_TEST_ALL_PREFIXES(SafeBrowsingStoreFileTest, PrefixMinMax); |
| FRIEND_TEST_ALL_PREFIXES(SafeBrowsingStoreFileTest, SubKnockout); |
| FRIEND_TEST_ALL_PREFIXES(SafeBrowsingStoreFileTest, Version7); |
| FRIEND_TEST_ALL_PREFIXES(SafeBrowsingStoreFileTest, Version8); |
| |
| // Maximum number of consecutive deltas to encode before generating |
| // a new index entry. This helps keep the worst-case performance |
| // for |Exists()| under control. |
| static const size_t kMaxRun = 100; |
| |
| // Helpers to make |index_| easier to deal with. |
| typedef std::pair<SBPrefix, uint32_t> IndexPair; |
| typedef std::vector<IndexPair> IndexVector; |
| static bool PrefixLess(const IndexPair& a, const IndexPair& b); |
| |
| // Helper to let |PrefixSetBuilder| add a run of data. |index_prefix| is |
| // added to |index_|, with the other elements added into |deltas_|. |
| void AddRun(SBPrefix index_prefix, |
| const uint16_t* run_begin, |
| const uint16_t* run_end); |
| |
| // |true| if |prefix| is one of the prefixes passed to the set's builder. |
| // Provided for testing purposes. |
| bool PrefixExists(SBPrefix prefix) const; |
| |
| // Regenerate the vector of prefixes passed to the constructor into |
| // |prefixes|. Prefixes will be added in sorted order. Useful for testing. |
| void GetPrefixes(std::vector<SBPrefix>* prefixes) const; |
| |
| // Used by |PrefixSetBuilder|. |
| PrefixSet(); |
| |
| // Helper for |LoadFile()|. Steals vector contents using |swap()|. |
| PrefixSet(IndexVector* index, |
| std::vector<uint16_t>* deltas, |
| std::vector<SBFullHash>* full_hashes); |
| |
| // Top-level index of prefix to offset in |deltas_|. Each pair |
| // indicates a base prefix and where the deltas from that prefix |
| // begin in |deltas_|. The deltas for a pair end at the next pair's |
| // index into |deltas_|. |
| IndexVector index_; |
| |
| // Deltas which are added to the prefix in |index_| to generate |
| // prefixes. Deltas are only valid between consecutive items from |
| // |index_|, or the end of |deltas_| for the last |index_| pair. |
| std::vector<uint16_t> deltas_; |
| |
| // Full hashes ordered by SBFullHashLess. |
| std::vector<SBFullHash> full_hashes_; |
| |
| DISALLOW_COPY_AND_ASSIGN(PrefixSet); |
| }; |
| |
| // Helper to incrementally build a PrefixSet from a stream of sorted prefixes. |
| class PrefixSetBuilder { |
| public: |
| PrefixSetBuilder(); |
| ~PrefixSetBuilder(); |
| |
| // Helper for unit tests and format conversion. |
| explicit PrefixSetBuilder(const std::vector<SBPrefix>& prefixes); |
| |
| // Add a prefix to the set. Prefixes must arrive in ascending order. |
| // Duplicate prefixes are dropped. |
| void AddPrefix(SBPrefix prefix); |
| |
| // Flush any buffered prefixes, and return the final PrefixSet instance. |
| // |hashes| are sorted and stored in |full_hashes_|. Any call other than the |
| // destructor is illegal after this call. |
| scoped_ptr<const PrefixSet> GetPrefixSet( |
| const std::vector<SBFullHash>& hashes); |
| |
| // Helper for clients which only track prefixes. Calls GetPrefixSet() with |
| // empty hash vector. |
| scoped_ptr<const PrefixSet> GetPrefixSetNoHashes(); |
| |
| private: |
| // Encode a run of deltas for |AddRun()|. The run is broken by a too-large |
| // delta, or kMaxRun, whichever comes first. |
| void EmitRun(); |
| |
| // Buffers prefixes until enough are avaliable to emit a run. |
| std::vector<SBPrefix> buffer_; |
| |
| // The PrefixSet being built. |
| scoped_ptr<PrefixSet> prefix_set_; |
| }; |
| |
| } // namespace safe_browsing |
| |
| #endif // COMPONENTS_SAFE_BROWSING_DB_PREFIX_SET_H_ |