[tor-bugs] #4439 [Metrics Utilities]: Develop a Java/Python API that wraps relay descriptor sources and provides unified access to them

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#4439: Develop a Java/Python API that wraps relay descriptor sources and provides
unified access to them
-------------------------------+--------------------------------------------
 Reporter:  karsten            |          Owner:  karsten
     Type:  task               |         Status:  new    
 Priority:  normal             |      Milestone:         
Component:  Metrics Utilities  |        Version:         
 Keywords:                     |         Parent:         
   Points:                     |   Actualpoints:         
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Comment(by atagar):

 > Can you be more precise what parts you misunderstood?

 Since this was spawned by the alarming infrastructure ticket I thought in
 the initial comment that we were talking about an RPC for services (like
 the alarms) to request information from the metrics hosts, and that this
 was an API for that. So disregard, it's obvious that has nothing to do
 with this. :)

 > I don't think we're talking about completely distinct functionality, are
 we?

 Hmmm... now I think we've just had another misunderstanding. I'm saying
 that it *is* related functionality and I'd be happy to hack on it as part
 of stem.

 My plan was to have Relay objects which are a composite of three things...
 - fingerprint (constructor arg, always there)
 - consensus and descriptor data (lazily loaded, throws an exception or
 returns a default value if it can't be loaded)

 {{{
 Relay
 |- __init__(fingerprint, raise_exc = False, default = None)
 |- load_consensus() - eager fetch for consensus data, returning a boolen
 for if it succeeds or not
 |- load_descriptor() - same for the descriptor
 |- fingerprint()
 |- exit_policy()
 |- contact_info()
 +- ... etc, getters for the union of the descriptor and consensus

 created() => unix timestamp for when the currently accessible consensus
 was created
 valid_until() => unix timestamp for when this consensus expires
 get_relays() => list of all Relay instances
 get_relay(fingerprint) => provides Relay instance for the given
 fingerprint
 get_relay_dest(ip_address, port) => provides Relay at the given ip/port
 ... probably a few other things I haven't thought of yet...
 }}}

 It sounds like we then simply need a factory for the data source that has
 those methods. Something like...

 {{{
 class ConsensusFetcher:
   """
   Abstract parent for factories that retrieve consensus data.
   """

   def created(self): pass
   def valid_until(self): pass
   def get_relays(self): pass
   def get_relay(fingerprint): pass
   def get_relay_dest(ip_address, port): pass

 class CacheFetcher(ConsensusFetcher):
   def __init__(path):
     """
     Retrieves consensus data from the local filesystem, via cached
 consensus
     files. This raises an IOError if we're unable to read the given data
     directory.
     """

     if not os.path.exists(path): raise IOError("%s doesn't exist" % path)
     # etc for implementation details

 class ControlFetcher(ConsensusFetcher):
   def __init__(control_connection):
     # ... similar for the control connection. This is important because
 there
     # could be instances where we don't have read access to tor's data
     # directory, but can access the control socket.

 class DirectoryServerFetcher(ConsensusFetcher):
   def __init__(address, port):
     # ... similar for fetching directly from a directory authority or
 mirror.
     # This one would have a little more options compared to the others...

   def is_current(self):
     # True if we're working from the most recent consensus, False
 otherwise.

   def fetch(self):
     # Retrieves the new consensus, raising an IOError if unable to do so.
 }}}

 Does that jive with what you were thinking of?

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/4439#comment:5>
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