Implementing EvictedDomainCookieCounter to keep user metrics on cookie eviction and reinstatement.

net/cookies/evicted_domain_cookie_counter.h

+// Copyright 2013 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 NET_COOKIES_EVICTED_DOMAIN_COOKIE_COUNTER_
+#define NET_COOKIES_EVICTED_DOMAIN_COOKIE_COUNTER_
+
+#include <map>
+#include <string>
+
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/time.h"
+#include "net/cookies/canonical_cookie.h"

[erikwright (departed), 2013/03/21 19:22:19]

forward-decl

[huangs, 2013/03/21 22:08:09]

Done.

+#include "net/cookies/cookie_monster.h"
+
+namespace net {
+
+// The Evicted Domain Cookie Counter generates statistics on "wrongly evicted"
+// cookies, i.e., cookies that were "evicted" (on reacking domain cookie limit)

[erikwright (departed), 2013/03/21 19:22:19]

typo

[huangs, 2013/03/21 22:08:09]

Done.

+// but are then "reinstated" later by a website because they were important.
+// Here is a specific scenario: a long-lived login session cookie gets evicted
+// due to its age, thereby forcing the user to lose session, and is reinstated
+// when the annoyed user reauthenticates.
+//
+// A solution to the above problem is the Cookie Priority Field, which gives
+// server a way to protect important cookies, thereby decreasing the chance
+// that these cookies are wrongly evicted. To measure the effictive of this
+// solution, we record eviction statistics before vs. after the fix.
+//
+// Specifically, we wish to record statistics on "reinstatement delay", i.e.,
+// the duration between eviction and reinstatement of cookie. We expect that
+// after the fix, average reinstantement delay will increase, since low priority
+// cookies are less likely to be reinstated after eviction.
+//
+// Statistics for Google domains are tracked separately.
+//
+class NET_EXPORT EvictedDomainCookieCounter : public CookieMonster::Delegate {
+ public:
+  // Structure to store sanitized (no cookie value) data from CanonicalCookie.

[erikwright (departed), 2013/03/21 19:22:19]

parenthetical is unnecessary

[huangs, 2013/03/21 22:08:09]

Done.

+  struct EvictedCookie {
+    base::Time eviction_time_;
+    base::Time expiry_time_;
+    bool is_google_;
+
+    EvictedCookie(base::Time eviction_time,
+                  base::Time expiry_time,
+                  bool is_google)
+        : eviction_time_(eviction_time),
+          expiry_time_(expiry_time),
+          is_google_(is_google) {}
+
+    void set_expired() {
+      expiry_time_ = base::Time::UnixEpoch();
+    }
+    bool is_expired(const base::Time& current) {
+      return !expiry_time_.is_null() && current >= expiry_time_;
+    }
+  };
+
+  class Delegate {
+   public:

[erikwright (departed), 2013/03/21 19:22:19]

Needs a virtual destructor.

[huangs, 2013/03/21 22:08:09]

Done.  Making it public instead of protected (else it won't compile due to
scoped_ptr<T> complaining).

+    // Called when a stored evicted cookie is reinstated.
+    virtual void Report(const EvictedCookie& dc,
+                        const base::Time& reinstatement_time) = 0;
+
+    // Getter of time is placed here to enable mocks.
+    virtual base::Time CurrentTime() = 0;
+  };
+
+  // Identifier of an evicted cookie. Can be obtained from GetKey().

[erikwright (departed), 2013/03/21 19:22:19]

These typedefs can be private, right?

[huangs, 2013/03/21 22:08:09]

Done.

+  typedef std::string EvictedCookieKey;
+
+  // Storage class of evicted cookie.
+  typedef std::map<EvictedCookieKey, EvictedCookie*> EvictedCookieMap;
+
+  explicit EvictedDomainCookieCounter(CookieMonster::Delegate* next_delegate);

[erikwright (departed), 2013/03/21 19:22:19]

make scoped_refptr<CookieMonster::Delegate>

[huangs, 2013/03/21 22:08:09]

Done.

+
+  EvictedDomainCookieCounter(
+      scoped_refptr<CookieMonster::Delegate> next_delegate,

[erikwright (departed), 2013/03/21 19:22:19]

ref_counted.h

[huangs, 2013/03/21 22:08:09]

Done.

+      scoped_ptr<Delegate> reporter,

[erikwright (departed), 2013/03/21 19:22:19]

scoped_ptr.h

[huangs, 2013/03/21 22:08:09]

Done.

+      size_t max_size,
+      size_t purge_count);
+
+  // Returns whether or not |cc| is a cookie from Google.
+  static bool IsGoogleCookie(const CanonicalCookie& cc);
+
+  // Returns the number of evicted cookies stored.
+  size_t GetStorageSize() const;
+
+  // CookieMonster::Delegate implementation.
+  virtual void OnCookieChanged(const CanonicalCookie& cc,
+                               bool removed,
+                               ChangeCause cause) OVERRIDE;

[erikwright (departed), 2013/03/21 19:22:19]

compiler_specific.h for OVERRIDE

[huangs, 2013/03/21 22:08:09]

Done.

+
+ private:
+  ~EvictedDomainCookieCounter();
+
+  // Computes a key for |cc| compatible with CanonicalCookie::IsEquivalent(),
+  // i.e., IsEquivalent(a, b) ==> GetKey(a) == GetKey(b).
+  static EvictedCookieKey GetKey(const CanonicalCookie& cc);
+
+  // Deallocates and removes an evicted cookie with given |key| if it is stored.
+  void FreeEvictedCookie(const EvictedCookieKey& key);
+
+  // Deallocates and removes all expired evicted cookies.
+  void FreeExpiredEvictedCookies(base::Time time_bound);
+
+  // If too many evicted cookies are stored, delete the expired oens, then
+  // delete cookies that were evicted the longest, until size limit reached.
+  void GarbageCollect(const base::Time& current);
+
+  // Called when a cookie is evicted. Adds the evicted cookie to storage,
+  // possibly replacing an existing evicted cookie.
+  void StoreEvictedCookie(const EvictedCookieKey& key,
+                          const CanonicalCookie& cc,
+                          const base::Time& current);
+
+  // Called when a new cookie is added, i.e., reinstatement may occur.
+  // Returns true iff the reinstatement takes place.
+  bool ProcessCookieReinstatement(const EvictedCookieKey& key,
+                                  const CanonicalCookie& cc,
+                                  const base::Time& current);
+
+  // For chaining the OnCookieChanged() event.
+  scoped_refptr<CookieMonster::Delegate> next_delegate_;
+
+  // On reinstatement, data are passed here to report reinstatement delay.
+  scoped_ptr<Delegate> reporter_;
+
+  // In-memory-only buffer to store sanitized (no cookie value) evicted cookies.
+  EvictedCookieMap evicted_cookies_;
+
+  // Capacity of the evicted cookie storage.
+  const size_t max_size_;
+
+  // Minimum amount to decrease evicted cookie storage, on garbage collection.
+  const size_t purge_count_;
+
+  DISALLOW_COPY_AND_ASSIGN(EvictedDomainCookieCounter);

[erikwright (departed), 2013/03/21 19:22:19]

basictypes.h

[huangs, 2013/03/21 22:08:09]

Done.

+};
+
+}  // namespace net
+
+#endif // NET_COOKIES_EVICTED_DOMAIN_COOKIE_COUNTER_