Added support for an optimistic protocol message from the client.

This allows the client to avoid a round-trip to the server by preemptively sending the first message of its preferred protocol exchange. This functionality is required by the pairing authenticator, coming soon to a code review near you.

BUG=156182

Review URL: https://chromiumcodereview.appspot.com/15085018

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@199908 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 36 insertions, 11 deletions

diff --git a/remoting/protocol/negotiating_client_authenticator.cc b/remoting/protocol/negotiating_client_authenticator.cc
index 5ab0507..af5d56b 100644
--- a/remoting/protocol/negotiating_client_authenticator.cc
+++ b/remoting/protocol/negotiating_client_authenticator.cc
@@ -62,11 +62,13 @@ void NegotiatingClientAuthenticator::ProcessMessage(
     current_method_ = method;
     method_set_by_host_ = true;
     state_ = PROCESSING_MESSAGE;
+
     // Copy the message since the authenticator may process it asynchronously.
-    CreateAuthenticator(WAITING_MESSAGE, base::Bind(
+    base::Closure callback = base::Bind(
         &NegotiatingAuthenticatorBase::ProcessMessageInternal,
         base::Unretained(this), base::Owned(new buzz::XmlElement(*message)),
-        resume_callback));
+        resume_callback);
+    CreateAuthenticatorForCurrentMethod(WAITING_MESSAGE, callback);
     return;
   }
   ProcessMessageInternal(message, resume_callback);
@@ -76,12 +78,18 @@ scoped_ptr<buzz::XmlElement> NegotiatingClientAuthenticator::GetNextMessage() {
   DCHECK_EQ(state(), MESSAGE_READY);
   // This is the first message to the host, send a list of supported methods.
   if (!current_method_.is_valid()) {
-    // We currently send just an empty message with the supported list, but, in
-    // the future, the client may optimistically pick a method and send its
-    // first message, along with the supported methods. If the host doesn't
-    // support that method, it is free to ignore this first message and pick a
-    // different method from the supported list.
-    scoped_ptr<buzz::XmlElement> result = CreateEmptyAuthenticatorMessage();
+    // If no authentication method has been chosen, see if we can optimistically
+    // choose one.
+    scoped_ptr<buzz::XmlElement> result;
+    current_authenticator_ = CreatePreferredAuthenticator();
+    if (current_authenticator_) {
+      DCHECK(current_authenticator_->state() == MESSAGE_READY);
+      result = GetNextMessageInternal();
+    } else {
+      result = CreateEmptyAuthenticatorMessage();
+    }
+
+    // Include a list of supported methods.
     std::stringstream supported_methods(std::stringstream::out);
     for (std::vector<AuthenticationMethod>::iterator it = methods_.begin();
          it != methods_.end(); ++it) {
@@ -96,7 +104,7 @@ scoped_ptr<buzz::XmlElement> NegotiatingClientAuthenticator::GetNextMessage() {
   return GetNextMessageInternal();
 }
 
-void NegotiatingClientAuthenticator::CreateAuthenticator(
+void NegotiatingClientAuthenticator::CreateAuthenticatorForCurrentMethod(
     Authenticator::State preferred_initial_state,
     const base::Closure& resume_callback) {
   DCHECK(current_method_.is_valid());
@@ -115,6 +123,12 @@ void NegotiatingClientAuthenticator::CreateAuthenticator(
   }
 }
 
+scoped_ptr<Authenticator>
+NegotiatingClientAuthenticator::CreatePreferredAuthenticator() {
+  NOTIMPLEMENTED();
+  return scoped_ptr<Authenticator>();
+}
+
 void NegotiatingClientAuthenticator::CreateV2AuthenticatorWithSecret(
     Authenticator::State initial_state,
     const base::Closure& resume_callback,
diff --git a/remoting/protocol/negotiating_client_authenticator.h b/remoting/protocol/negotiating_client_authenticator.h
index d2047fe..995cf1dd 100644
--- a/remoting/protocol/negotiating_client_authenticator.h
+++ b/remoting/protocol/negotiating_client_authenticator.h
@@ -45,8 +45,19 @@ class NegotiatingClientAuthenticator : public NegotiatingAuthenticatorBase {
   // |current_authenticator_|. Authenticators that can be started in either
   // state will be created in |preferred_initial_state|.
   // |resume_callback| is called after |current_authenticator_| is set.
-  void CreateAuthenticator(Authenticator::State preferred_initial_state,
-                           const base::Closure& resume_callback);
+  void CreateAuthenticatorForCurrentMethod(
+      Authenticator::State preferred_initial_state,
+      const base::Closure& resume_callback);
+
+  // If possible, create a preferred authenticator ready to send an
+  // initial message optimistically to the host. The host is free to
+  // ignore the client's preferred authenticator and initial message
+  // and to instead reply with an alternative method. See the comments
+  // in negotiating_authenticator_base.h for more details.
+  //
+  // Returns the preferred authenticator if possible, or NULL otherwise.
+  scoped_ptr<Authenticator> CreatePreferredAuthenticator();
+
 
   // Creates a V2Authenticator in state |initial_state| with the given
   // |shared_secret|, then runs |resume_callback|.