TODO

- Warning header takes a code (300-399) a hostname (not user agent) and a
  message. Class allows any code (100-999) and we use engine.user_agent
  for the hostname where we use this header in session.py

- 202 is deprecated (see https://tools.ietf.org/html/rfc6665#page-43)

- After ICE negotiation completed we do not save state and later re-INVITEs
  can fail, we must send re-INVITE or UPDATE with chosen candidate

+ Allow resume of failed file transfers (a=file-range SDP attribute)

+ combine account.uri and account.contact into account.uri.aor and
  account.uri.contact. This will also remove the confusion between
  account.contact and account.contact_manager

+ change settings so they store changes in a thread local container
  which is made public (accessible for all threads) when save is called.
  This will make changes be atomic inside a thread (everything from 
  attribute changes up to the save operation is contained in the thread
  and will not mix with changes done in parallel from other threads).

+ there is a race condition that can prevent an account to start if it is
  created while the start method of SIPApplication runs and it passed the
  point where it called AccountManager.start. A quick workaround is to
  never create an account before SIPApplicationDidStart is posted

+ SIPApplication.start attempts to be restartable in case of errors, but
  there are cases where it may enter into a state where it will raise
  exceptions perpetually, even if the condition that led to the exception
  was fixed.

- allow deleting transport on SIPURI

- modify Invitation/Request/Subscription to reset transport on request_uri

- in application.py it subscribes to notifications but doesn't remove them
  when it stops

- End a session while in accepting state (requires session serialization)

- Model file transfer after desktop sharing (use handlers on termination)
  have internal/external handlers (notifications based or file bridges)

- Use an ordered dict for keeping accounts in the AccountManager ?!?
  see http://code.activestate.com/recipes/576693/

- send notifications when local/remote party becomes focus
  SIPSessionLocalPartyIsFocus, SIPSessionRemotePartyIsFocus

- have higher level notifications on conference events


To fix this exception:

sip:nwpsefvl@10.0.0.1:52067 52067
sip:nwpsefvl@10.0.0.1:52067 52067
sip:nwpsefvl@10.0.0.1;transport=tcp None
Traceback (most recent call last):
  File "/usr/lib/python2.5/site-packages/twisted/internet/base.py", line 778, in runUntilCurrent
    call.func(*call.args, **call.kw)
  File "/usr/lib/pymodules/python2.5/eventlet/hubs/twistedr.py", line 158, in call_if_greenlet_alive
    return func(*args1, **kwargs1)
  File "/usr/lib/pymodules/python2.5/eventlet/proc.py", line 571, in _run
    result = function(*args, **kwargs)
  File "/home/dan/work/voip/python-sipsimple/sipsimple/account.py", line 683, in _handle_commands
    handler(command)
  File "/home/dan/work/voip/python-sipsimple/sipsimple/account.py", line 720, in _CH_register
    txtRecord=bonjour.TXTRecord(items=txtdata))
  File "/home/dan/work/voip/blink-qt/sipsimple/bonjour.py", line 1125, in DNSServiceRegister
TypeError: an integer is required

- Notification from SIPApplication when a transport is added/removed to the
  engine.
- SIPApplication should provide a list of supported transports that need to
  be used instead of the ones from settings because not everything enabled
  in settings may actually be available at runtime on the engine
- Build contacts on above notification instead of building them on the fly

- Use OpenH264 implementation
    - We need the binaries?!

- Ability to start stream deactivated / on-hold
    - VideoStream(direction='sendrecv') like MSRP?
    - Review stream API, s/deactivate/shutdown/ ?

- Open the camera at its native framerate