Certificate Transparency: Notify STH Observers of known STHs

net/cert/sth_distributor.h

Index: net/cert/sth_distributor.h
diff --git a/net/cert/sth_distributor.h b/net/cert/sth_distributor.h
index 3d9691cc56c029a47c627f6aee0987d7e2b5c3cf..c1ba65cfb4f9ab7bead94b9272f2520f4bd770e1 100644
--- a/net/cert/sth_distributor.h
+++ b/net/cert/sth_distributor.h
@@ -14,6 +14,16 @@ namespace net {
 
 namespace ct {
 
+namespace internal {
+
+// Compares SignedTreeHeads by their log ID, to facilitate creation of a
+// map of STHs where there's only one STH for each log.
+struct STHLogIDComparator {
+  bool operator()(const SignedTreeHead& first, const SignedTreeHead& second);
+};
+
+}  // namespace internal

[Ryan Sleevi, 2016/05/12 19:51:28]

DESIGN: You don't need to expose this in a public class.

[Eran Messeri, 2016/05/13 09:04:08]

Done.

+
 // A proxy for delegating new STH notifications to all registered
 // observers.
 // For each |observer| registered with RegisterObserver, the
@@ -28,10 +38,20 @@ class NET_EXPORT STHDistributor : public STHObserver, public STHReporter {
   void NewSTHObserved(const SignedTreeHead& sth) override;
 
   // STHReporter implementation
+  // Registers |observer| for new STH notifications and invokes the
+  // new STH notification of this |observer| with observed STHs (one
+  // per log).
   void RegisterObserver(STHObserver* observer) override;
+
+  // Unregisters |observer|, should only be called with observers
+  // that were previously registered  via RegisterObserver;
   void UnregisterObserver(STHObserver* observer) override;
 
  private:
+  // Set of unique STHs from logs.
+  std::set<SignedTreeHead, internal::STHLogIDComparator> observed_sths_;

[Ryan Sleevi, 2016/05/12 19:51:28]

DESIGN: An std::set<> is pretty inefficient for your problem case, as it forces
a lot of dynamic allocation (for the red-black tree), forces the design issue
you see above (the internal), and doesn't substantially gain benefits.

We're talking a value of N < 10. A linear scan over a vector is perfectly fine

[Eran Messeri, 2016/05/13 09:04:08]

Done.

+
+  // The observers for new STH notifications.
   base::ObserverList<STHObserver> observer_list_;
 };