Move prefix_set and parts of s_b_util into a new component safe_browsing_db.

chrome/browser/safe_browsing/prefix_set.h

-// 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 CHROME_BROWSER_SAFE_BROWSING_PREFIX_SET_H_
-#define CHROME_BROWSER_SAFE_BROWSING_PREFIX_SET_H_
-
-#include <utility>
-#include <vector>
-
-#include "base/gtest_prod_util.h"
-#include "base/memory/scoped_ptr.h"
-#include "chrome/browser/safe_browsing/safe_browsing_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> 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* run_begin, const uint16* 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>* 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> 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  // CHROME_BROWSER_SAFE_BROWSING_PREFIX_SET_H_