Consistently suggest ephemeral port for QUIC client

net/quic/port_suggester.h

Index: net/quic/port_suggester.h
diff --git a/net/quic/port_suggester.h b/net/quic/port_suggester.h
new file mode 100644
index 0000000000000000000000000000000000000000..3eab184a050e9c04b530032b4122925f9f01abf5
--- /dev/null
+++ b/net/quic/port_suggester.h
@@ -0,0 +1,51 @@
+// 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_QUIC_PORT_SUGGESTER_H_
+#define NET_QUIC_PORT_SUGGESTER_H_
+
+#include "base/basictypes.h"
+#include "base/memory/ref_counted.h"
+#include "base/sha1.h"
+#include "net/base/net_export.h"
+
+namespace net {
+
+class HostPortPair;
+
+// We provide a pseudo-random number generator that is always seeded the same
+// way for a given destination host-port pair.  The generator is used to
+// consistently suggest (for that host-port pair) an ephemeral source port,
+// and hence increase the likelihood that a server's load balancer will direct
+// a repeated connection to the same server (with QUIC, further increasing the
+// chance of connection establishment with 0-RTT).
+class NET_EXPORT PortSuggester

[Ryan Hamilton, 2013/12/07 23:21:55]

Should this be NET_EXPORT or NET_EXPORT_PRIVATE?  If you do not intend to use it
outside of net/, I think you can make it PRIVATE.

[jar (doing other things), 2013/12/08 01:38:36]

Done.

+    : public base::RefCounted<PortSuggester> {

[Ryan Hamilton, 2013/12/07 23:21:55]

nit: I think this can all fit on a single line.  (Unless you make it private :>)

[jar (doing other things), 2013/12/08 01:38:36]

Made private... doesn't fit.

+ public:
+  // |per_profile_randomness| is used to seed the generator.
+  PortSuggester(const HostPortPair& server, uint64 per_profile_randomness);
+
+  // Generate a pseudo-random int in the inclusive range from |min| to |max|.
+  // Will (probably) return different numbers when called repeatedly.
+  int SuggestPort(int min, int max);
+
+  uint32 call_count() const { return call_count_; }
+  int previous_suggestion() const { return previous_suggestion_; }

[Ryan Hamilton, 2013/12/07 23:21:55]

if you decide to keep this method, should it DCHECK_LT(0u, call_count_)?

[jar (doing other things), 2013/12/08 01:38:36]

I can add that.  I gave it a init value of -1, so that it would be sure to fail
when compared with plausible ports that get use.

I'll add the DCHECK().

+
+ private:
+  friend class base::RefCounted<PortSuggester>;
+
+  virtual ~PortSuggester() {}
+
+  // We maintain the first 8 bytes of a hash as our seed_ state.
+  uint64  seed_;

[Ryan Hamilton, 2013/12/07 23:21:55]

nit: extra space before seed_;

[jar (doing other things), 2013/12/08 01:38:36]

Done.

+  uint32 call_count_;  // Number of suggestions made.
+  int previous_suggestion_;
+
+  DISALLOW_COPY_AND_ASSIGN(PortSuggester);
+};
+
+}  // namespace net
+
+#endif  // NET_QUIC_PORT_SUGGESTER_H_