Make all quota-exceeding messages in the storage API explain what the failure

chrome/browser/extensions/extensions_quota_service.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.
 
 // The ExtensionsQuotaService uses heuristics to limit abusive requests
 // made by extensions.  In this model 'items' (e.g individual bookmarks) are
 // represented by a 'Bucket' that holds state for that item for one single
 // interval of time.  The interval of time is defined as 'how long we need to
 // watch an item (for a particular heuristic) before making a decision about
 // quota violations'.  A heuristic is two functions: one mapping input
@@ skipping 34 matching lines @@
   // Some concrete heuristics (declared below) that ExtensionFunctions can
   // use to help the service make decisions about quota violations.
   class TimedLimit;
   class SustainedLimit;
 
   ExtensionsQuotaService();
   virtual ~ExtensionsQuotaService();
 
   // Decide whether the invocation of |function| with argument |args| by the
   // extension specified by |extension_id| results in a quota limit violation.
-  // Returns true if the request is fine and can proceed, false if the request
-  // should be throttled and an error returned to the extension.
-  bool Assess(const std::string& extension_id, ExtensionFunction* function,
-              const ListValue* args, const base::TimeTicks& event_time);
+  // Returns an error message representing the failure if quota was exceeded,
+  // or empty-string if the request is fine and can proceed.
+  std::string Assess(const std::string& extension_id,
+                     ExtensionFunction* function,
+                     const ListValue* args,
+                     const base::TimeTicks& event_time);
+
  private:
   friend class extensions::TestResetQuotaFunction;
   typedef std::string ExtensionId;
   typedef std::string FunctionName;
   // All QuotaLimitHeuristic instances in this map are owned by us.
   typedef std::map<FunctionName, QuotaLimitHeuristics> FunctionHeuristicsMap;
 
-  // Purge resets all accumulated data (except |violators_|) as if the service
-  // was just created. Called periodically so we don't consume an unbounded
-  // amount of memory while tracking quota.  Yes, this could mean an extension
-  // gets away with murder if it is timed right, but the extensions we are
-  // trying to limit are ones that consistently violate, so we'll converge
-  // to the correct set.
+  // Purge resets all accumulated data (except |violation_errors_|) as if the
+  // service was just created. Called periodically so we don't consume an
+  // unbounded amount of memory while tracking quota.  Yes, this could mean an
+  // extension gets away with murder if it is timed right, but the extensions
+  // we are trying to limit are ones that consistently violate, so we'll
+  // converge to the correct set.
   void Purge();
   void PurgeFunctionHeuristicsMap(FunctionHeuristicsMap* map);
   base::RepeatingTimer<ExtensionsQuotaService> purge_timer_;
 
   // Our quota tracking state for extensions that have invoked quota limited
   // functions.  Each extension is treated separately, so extension ids are the
   // key for the mapping.  As an extension invokes functions, the map keeps
   // track of which functions it has invoked and the heuristics for each one.
   // Each heuristic will be evaluated and ANDed together to get a final answer.
   std::map<ExtensionId, FunctionHeuristicsMap> function_heuristics_;
 
   // For now, as soon as an extension violates quota, we don't allow it to
   // make any more requests to quota limited functions.  This provides a quick
   // lookup for these extensions that is only stored in memory.
-  base::hash_set<std::string> violators_;
+  typedef std::map<std::string, std::string> ViolationErrorMap;
+  ViolationErrorMap violation_errors_;
 
   DISALLOW_COPY_AND_ASSIGN(ExtensionsQuotaService);
 };
 
 // A QuotaLimitHeuristic is two things: 1, A heuristic to map extension
 // function arguments to corresponding Buckets for each input arg, and 2) a
 // heuristic for determining if a new event involving a particular item
 // (represented by its Bucket) constitutes a quota violation.
 class QuotaLimitHeuristic {
  public:
@@ skipping 33 matching lines @@
     // The time at which the token count and next expiration should be reset,
     // via a call to Reset.
     const base::TimeTicks& expiration() { return expiration_; }
    private:
     base::TimeTicks expiration_;
     int64 num_tokens_;
     DISALLOW_COPY_AND_ASSIGN(Bucket);
   };
   typedef std::list<Bucket*> BucketList;
 
-  // A generic error message for quota violating requests.
-  static const char kGenericOverQuotaError[];
-
   // A helper interface to retrieve the bucket corresponding to |args| from
   // the set of buckets (which is typically stored in the BucketMapper itself)
   // for this QuotaLimitHeuristic.
   class BucketMapper {
    public:
     virtual ~BucketMapper() {}
     // In most cases, this should simply extract item IDs from the arguments
     // (e.g for bookmark operations involving an existing item). If a problem
     // occurs while parsing |args|, the function aborts - buckets may be non-
     // empty). The expectation is that invalid args and associated errors are
     // handled by the ExtensionFunction itself so we don't concern ourselves.
     virtual void GetBucketsForArgs(const ListValue* args,
                                    BucketList* buckets) = 0;
   };
 
   // Maps all calls to the same bucket, regardless of |args|, for this
   // QuotaLimitHeuristic.
   class SingletonBucketMapper : public BucketMapper {
    public:
     SingletonBucketMapper() {}
     virtual ~SingletonBucketMapper() {}
     virtual void GetBucketsForArgs(const ListValue* args,
                                    BucketList* buckets) OVERRIDE;
 
    private:
     Bucket bucket_;
     DISALLOW_COPY_AND_ASSIGN(SingletonBucketMapper);
   };
 
-  // Ownership of |mapper| is given to the new QuotaLimitHeuristic.
-  QuotaLimitHeuristic(const Config& config, BucketMapper* map);
+  // Ownership of |map| is given to the new QuotaLimitHeuristic.
+  QuotaLimitHeuristic(const Config& config,
+                      BucketMapper* map,
+                      const std::string& name);
   virtual ~QuotaLimitHeuristic();
 
   // Determines if sufficient quota exists (according to the Apply
   // implementation of a derived class) to perform an operation with |args|,
   // based on the history of similar operations with similar arguments (which
   // is retrieved using the BucketMapper).
   bool ApplyToArgs(const ListValue* args, const base::TimeTicks& event_time);
 
+  // Returns an error formatted according to this heuristic.
+  std::string GetError() const;
+
  protected:
   const Config& config() { return config_; }
 
   // Determine if the new event occurring at |event_time| involving |bucket|
   // constitutes a quota violation according to this heuristic.
   virtual bool Apply(Bucket* bucket, const base::TimeTicks& event_time) = 0;
 
  private:
   friend class QuotaLimitHeuristicTest;
 
   const Config config_;
 
-  // The mapper used in Map.  Cannot be NULL.
+  // The mapper used in Map. Cannot be NULL.
   scoped_ptr<BucketMapper> bucket_mapper_;
 
+  // The name of the heuristic for formatting error messages.
+  std::string name_;
+
   DISALLOW_COPY_AND_ASSIGN(QuotaLimitHeuristic);
 };
 
 // A simple per-item heuristic to limit the number of events that can occur in
 // a given period of time; e.g "no more than 100 events in an hour".
 class ExtensionsQuotaService::TimedLimit : public QuotaLimitHeuristic {
  public:
-  TimedLimit(const Config& config, BucketMapper* map)
-      : QuotaLimitHeuristic(config, map) {}
+  TimedLimit(const Config& config, BucketMapper* map, const std::string& name)
+      : QuotaLimitHeuristic(config, map, name) {}
   virtual bool Apply(Bucket* bucket,
                      const base::TimeTicks& event_time) OVERRIDE;
 };
 
 // A per-item heuristic to limit the number of events that can occur in a
 // period of time over a sustained longer interval. E.g "no more than two
 // events per minute, sustained over 10 minutes".
 class ExtensionsQuotaService::SustainedLimit : public QuotaLimitHeuristic {
  public:
   SustainedLimit(const base::TimeDelta& sustain,
                  const Config& config,
-                 BucketMapper* map);
+                 BucketMapper* map,
+                 const std::string& name);
   virtual bool Apply(Bucket* bucket,
                      const base::TimeTicks& event_time) OVERRIDE;
  private:
   // Specifies how long exhaustion of buckets is allowed to continue before
   // denying requests.
   const int64 repeat_exhaustion_allowance_;
   int64 num_available_repeat_exhaustions_;
 };
 
 #endif  // CHROME_BROWSER_EXTENSIONS_EXTENSIONS_QUOTA_SERVICE_H_