Implement exponential backoff for failed Me2Me authentication attempts

remoting/protocol/session_manager.h

 // Copyright (c) 2012 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.
 
 // The purpose of SessionManager is to facilitate creation of chromotocol
 // sessions. Both host and client use it to establish chromotocol
 // sessions. JingleChromotocolServer implements this inteface using
 // libjingle.
 //
 // OUTGOING SESSIONS
@@ skipping 92 matching lines @@
 // Generic interface for Chromoting session manager.
 //
 // TODO(sergeyu): Split this into two separate interfaces: one for the
 // client side and one for the host side.
 class SessionManager : public base::NonThreadSafe {
  public:
   SessionManager() { }
   virtual ~SessionManager() { }
 
   enum IncomingSessionResponse {
+    // Accept the session.
     ACCEPT,
+
+    // Reject the session due to incompatible session configuration.
     INCOMPATIBLE,
+
+    // Reject the session because the host is currently disabled due
+    // to previous login attempts.
+    DISABLED,

[Wez, 2012/03/27 16:23:56]

nit: "DISABLED" seems like a bad name for this, since that's the term we
generally use when the host is stopped (i.e. not online).  "OVERLOAD" or
"UNAVAILABLE" might be better terms.

[Sergey Ulanov, 2012/03/27 18:00:52]

There is HOST_IS_OFFLINE error code that we use to indicate that the host is
offline, so I don't think HOST_IS_DISABLED can be confusing. IMHO distinction
between UNAVAILABLE and OFFLINE is even less clear. 
I've renamed this particular value to UNAVAILABLE, but kept HOST_IS_DISABLED
error code  - changing it now would require merging to the M19 branch as we use
these names for interaction between the client plugin and webapp. We can still
do if you feel strongly about it.

[Wez, 2012/03/27 19:49:41]

If we have "offline" and "disabled" then it's natural for a reader to assume
that DISABLED means the user explicitly disabled the host, and that OFFLINE
means that the host is enabled but not online for some reason.
I'd be fine with OVERLOAD[ED]. ;)

"unavailable" and "offline" have overlapping meanings, but "offline" is pretty
specific - it's saying the host is actually offline.  "unavailable" is more
specific, meaning it's online but not currently available - that might be
re-usable to mean that the host is in-use if we ever wanted to provide
floor-control for access to hosts.
I do think that HOST_IS_DISABLED is a very confusing name - it suggests that the
host is installed & configured, but not enabled right now, rather than that it
has automatically stopped accepting connections.

+
+    // Reject the session because the client is not allowed to connect
+    // to the host.
     DECLINE,
   };
 
   class Listener {
    public:
     Listener() { }
     ~Listener() { }
 
     // Called when the session manager is ready to create outgoing
     // sessions. May be called from Init() or after Init()
@@ skipping 46 matching lines @@
       scoped_ptr<AuthenticatorFactory> authenticator_factory) = 0;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(SessionManager);
 };
 
 }  // namespace protocol
 }  // namespace remoting
 
 #endif  // REMOTING_PROTOCOL_SESSION_MANAGER_H_