Add new API function: feedbackPrivate.readLogSource

chrome/browser/extensions/api/feedback_private/log_source_access_manager.h

+// Copyright 2017 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 CHROME_BROWSER_EXTENSIONS_API_FEEDBACK_PRIVATE_LOG_SOURCE_ACCESS_MANAGER_H_
+#define CHROME_BROWSER_EXTENSIONS_API_FEEDBACK_PRIVATE_LOG_SOURCE_ACCESS_MANAGER_H_
+
+#include <map>
+#include <set>
+#include <string>
+#include <utility>
+
+#include "base/callback.h"
+#include "base/macros.h"
+#include "base/memory/weak_ptr.h"
+#include "base/time/tick_clock.h"
+#include "base/time/time.h"
+#include "chrome/common/extensions/api/feedback_private.h"
+
+namespace extensions {
+
+// Provides bookkeepping for the rules of surrounding the use of
+// SingleLogSources:
+// - Each extension can have only one SingleLogSource for a particular source.
+// - A source may not be accessed too frequently by an extension.
+class LogSourceAccessManager {
+ public:
+  // Every source/extension_id pair is linked to a unique SingleLogSource.
+  struct SourceAndExtension {
+    explicit SourceAndExtension(api::feedback_private::LogSource source,
+                                const std::string& extension_id);
+
+    bool operator<(const SourceAndExtension& other) const {
+      return std::make_pair(source, extension_id) <
+             std::make_pair(other.source, other.extension_id);
+    }
+
+    api::feedback_private::LogSource source;
+    std::string extension_id;
+  };
+
+  LogSourceAccessManager();
+  ~LogSourceAccessManager();
+
+  // To override the default rate-limiting mechanism of this function, pass in
+  // a TimeDelta representing the desired minimum time between consecutive reads
+  // of a source from an extension. Does not take ownership of |timeout|. When
+  // done testing, call this function again with |timeout|=nullptr to reset to
+  // the default behavior.
+  static void SetRateLimitingTimeoutForTesting(const base::TimeDelta* timeout);
+
+  // Add a source/extension pair to |active_keys_|. Returns true if there was no
+  // existing entry, or false otherwise.
+  bool AddExtension(const SourceAndExtension& key);
+
+  // Removes a source/extension pair from |active_keys_|. Returns true if
+  // there an existing entry, or false otherwise.
+  bool RemoveExtension(const SourceAndExtension& key);
+
+  // Returns the number of entries in |active_keys_| with source=|source|.
+  size_t GetNumActiveExtensionsForSource(
+      api::feedback_private::LogSource source) const;
+
+  // Attempts to update the entry for |key| in |last_access_times_| to the
+  // current time, to record that the source is being accessed by the extension
+  // right now. If less than |min_time_between_reads_| has elapsed since the
+  // last successful read, do not update the timestamp in |last_access_times_|,
+  // and instead return false. Otherwise returns true.
+  //
+  // Creates a new entry in |last_access_times_| if it doesn't exist. Will not
+  // delete from |last_access_times_|.
+  bool AccessSourceFromExtension(const SourceAndExtension& key);
+
+  // Returns the last time that |key.source| was accessed by |key.extension|.
+  // If it was never accessed by the extension, returns an empty base::Time
+  // object.
+  base::TimeTicks GetLastExtensionAccessTime(
+      const SourceAndExtension& key) const;
+
+  // Returns a closure (callback with no args) that removes |key| from this
+  // LogSourceAccessManager. This so that when ApiResourceManager automatically
+  // deletes its entries that track SingleLogSources, it can update the
+  // bookkeeping entries in LogSourceAccessManager.
+  base::Closure GetUnregisterCallback(const SourceAndExtension& key);
+
+  // Takes ownership of |clock|.
+  void set_tick_clock(std::unique_ptr<base::TickClock> clock) {
+    tick_clock_.reset(clock.release());
+  }
+
+ private:
+  // Calls RemoveExtension() but discards the return value. Used to generate the
+  // closure that is returned by GetUnregisterCallback.
+  void RemoveExtensionNoReturn(const SourceAndExtension& key);
+
+  // Contains all source/extension pairs for which a SingleLogSource has been
+  // created and not yet destroyed (i.e. still in use).
+  std::set<SourceAndExtension> active_keys_;
+
+  // Keeps track of the last time each source was accessed by each extension.
+  // Does not get updated when the actual SingleLogSource is accessed. Instead,
+  // explicitly call AccessSourceFromExtension() at the time of accessing the
+  // SingleLogSource.
+  //
+  // This intentionally kept separate from |active_keys_| because entries can be
+  // removed from and re-added to |active_keys_|, but that should not erase the
+  // recorded access times.
+  std::map<SourceAndExtension, base::TimeTicks> last_access_times_;
+
+  // Provides a timer clock implementation for keeping track of access times.
+  // Can override the default clock for testing.
+  std::unique_ptr<base::TickClock> tick_clock_;
+
+  base::WeakPtrFactory<LogSourceAccessManager> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(LogSourceAccessManager);
+};
+
+}  // namespace extensions
+
+#endif  // CHROME_BROWSER_EXTENSIONS_API_FEEDBACK_PRIVATE_LOG_SOURCE_ACCESS_MANAGER_H_