Index: sync/internal_api/public/base/unique_position.h |
diff --git a/sync/internal_api/public/base/unique_position.h b/sync/internal_api/public/base/unique_position.h |
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index 70e9b39e09d25ba8e480aff8a769b52cb5c2e56e..0000000000000000000000000000000000000000 |
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-// 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. |
- |
-#ifndef SYNC_INTERNAL_API_PUBLIC_BASE_UNIQUE_POSITION_H_ |
-#define SYNC_INTERNAL_API_PUBLIC_BASE_UNIQUE_POSITION_H_ |
- |
-#include <stddef.h> |
-#include <stdint.h> |
- |
-#include <string> |
- |
-#include "sync/base/sync_export.h" |
- |
-namespace sync_pb { |
-class UniquePosition; |
-} |
- |
-namespace syncer { |
- |
-// A class to represent positions. |
-// |
-// Valid UniquePosition objects have the following properties: |
-// |
-// - a < b and b < c implies a < c (transitivity); |
-// - exactly one of a < b, b < a and a = b holds (trichotomy); |
-// - if a < b, there is a UniquePosition such that a < x < b (density); |
-// - there are UniquePositions x and y such that x < a < y (unboundedness); |
-// - if a and b were constructed with different unique suffixes, then a != b. |
-// |
-// As long as all UniquePositions used to sort a list were created with unique |
-// suffixes, then if any item changes its position in the list, only its |
-// UniquePosition value has to change to represent the new order, and all other |
-// values can stay the same. |
-// |
-// Note that the unique suffixes must be exactly |kSuffixLength| bytes long. |
-// |
-// The cost for all these features is potentially unbounded space usage. In |
-// practice, however, most ordinals should be not much longer than the suffix. |
-// |
-// This class currently has several bookmarks-related assumptions built in, |
-// though it could be adapted to be more generally useful. |
-class SYNC_EXPORT UniquePosition { |
- public: |
- static const size_t kSuffixLength; |
- static const size_t kCompressBytesThreshold; |
- |
- static bool IsValidSuffix(const std::string& suffix); |
- static bool IsValidBytes(const std::string& bytes); |
- |
- // Returns a valid, but mostly random suffix. |
- // Avoid using this; it can lead to inconsistent sort orderings if misused. |
- static std::string RandomSuffix(); |
- |
- // Returns an invalid position. |
- static UniquePosition CreateInvalid(); |
- |
- // Converts from a 'sync_pb::UniquePosition' protobuf to a UniquePosition. |
- // This may return an invalid position if the parsing fails. |
- static UniquePosition FromProto(const sync_pb::UniquePosition& proto); |
- |
- // Creates a position with the given suffix. Ordering among positions created |
- // from this function is the same as that of the integer parameters that were |
- // passed in. |
- static UniquePosition FromInt64(int64_t i, const std::string& suffix); |
- |
- // Returns a valid position. Its ordering is not defined. |
- static UniquePosition InitialPosition(const std::string& suffix); |
- |
- // Returns positions compare smaller than, greater than, or between the input |
- // positions. |
- static UniquePosition Before(const UniquePosition& x, |
- const std::string& suffix); |
- static UniquePosition After(const UniquePosition& x, |
- const std::string& suffix); |
- static UniquePosition Between(const UniquePosition& before, |
- const UniquePosition& after, |
- const std::string& suffix); |
- |
- // This constructor creates an invalid value. |
- UniquePosition(); |
- |
- bool LessThan(const UniquePosition& other) const; |
- bool Equals(const UniquePosition& other) const; |
- |
- // Serializes the position's internal state to a protobuf. |
- void ToProto(sync_pb::UniquePosition* proto) const; |
- |
- // Serializes the protobuf representation of this object as a string. |
- void SerializeToString(std::string* blob) const; |
- |
- // Returns a human-readable representation of this item's internal state. |
- std::string ToDebugString() const; |
- |
- // Returns the suffix. |
- std::string GetSuffixForTest() const; |
- |
- // Performs a lossy conversion to an int64_t position. Positions converted to |
- // and from int64_ts using this and the FromInt64 function should maintain |
- // their |
- // relative orderings unless the int64_t values conflict. |
- int64_t ToInt64() const; |
- |
- bool IsValid() const; |
- |
- private: |
- friend class UniquePositionTest; |
- |
- // Returns a string X such that (X ++ |suffix|) < |str|. |
- // |str| must be a trailing substring of a valid ordinal. |
- // |suffix| must be a valid unique suffix. |
- static std::string FindSmallerWithSuffix(const std::string& str, |
- const std::string& suffix); |
- // Returns a string X such that (X ++ |suffix|) > |str|. |
- // |str| must be a trailing substring of a valid ordinal. |
- // |suffix| must be a valid unique suffix. |
- static std::string FindGreaterWithSuffix(const std::string& str, |
- const std::string& suffix); |
- // Returns a string X such that |before| < (X ++ |suffix|) < |after|. |
- // |before| and after must be a trailing substrings of valid ordinals. |
- // |suffix| must be a valid unique suffix. |
- static std::string FindBetweenWithSuffix(const std::string& before, |
- const std::string& after, |
- const std::string& suffix); |
- |
- // Expects a run-length compressed string as input. For internal use only. |
- explicit UniquePosition(const std::string& internal_rep); |
- |
- // Expects an uncompressed prefix and suffix as input. The |suffix| parameter |
- // must be a suffix of |uncompressed|. For internal use only. |
- UniquePosition(const std::string& uncompressed, const std::string& suffix); |
- |
- // Implementation of an order-preserving run-length compression scheme. |
- static std::string Compress(const std::string& input); |
- static std::string CompressImpl(const std::string& input); |
- static std::string Uncompress(const std::string& compressed); |
- static bool IsValidCompressed(const std::string& str); |
- |
- // The position value after it has been run through the custom compression |
- // algorithm. See Compress() and Uncompress() functions above. |
- std::string compressed_; |
- bool is_valid_; |
-}; |
- |
-} // namespace syncer |
- |
-#endif // SYNC_INTERNAL_API_PUBLIC_BASE_UNIQUE_POSITION_H_ |