MicroDescriptor
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Parsing for Tor microdescriptors, which contain a distilled version of
a relay’s server descriptor. As of Tor version 0.2.3.3-alpha Tor no
longer downloads server descriptors by default, opting for
microdescriptors instead.

Unlike most descriptor documents these aren’t available on the metrics
site (since they don’t contain any information that the server
descriptors don’t).

The limited information in microdescriptors make them rather clunky to
use compared with server descriptors. For instance microdescriptors
lack the relay’s fingerprint, making it difficut to use them to look
up the relay’s other descriptors.

To do so you need to match the microdescriptor’s digest against its
corresponding router status entry. For added fun as of this writing
the controller doesn’t even surface those router status entries
(ticket 7953).

For instance, here’s an example that prints the nickname and
fingerprints of the exit relays.

   import os

   from stem.control import Controller
   from stem.descriptor import parse_file

   with Controller.from_port(port = 9051) as controller:
     controller.authenticate()

     exit_digests = set()
     data_dir = controller.get_conf('DataDirectory')

     for desc in controller.get_microdescriptors():
       if desc.exit_policy.is_exiting_allowed():
         exit_digests.add(desc.digest)

     print 'Exit Relays:'

     for desc in parse_file(os.path.join(data_dir, 'cached-microdesc-consensus')):
       if desc.digest in exit_digests:
         print '  %s (%s)' % (desc.nickname, desc.fingerprint)

Doing the same is trivial with server descriptors…

   from stem.descriptor import parse_file

   print 'Exit Relays:'

   for desc in parse_file('/home/atagar/.tor/cached-descriptors'):
     if desc.exit_policy.is_exiting_allowed():
       print '  %s (%s)' % (desc.nickname, desc.fingerprint)

**Module Overview:**

   Microdescriptor - Tor microdescriptor.
