MicroDescriptor
***************

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.

class stem.descriptor.microdescriptor.Microdescriptor(raw_contents, validate=False, annotations=None)

   Bases: "stem.descriptor.Descriptor"

   Microdescriptor (descriptor specification)

   Variables:
      * **onion_key** (*str*) – ***** key used to encrypt EXTEND
        cells

      * **ntor_onion_key** (*str*) – base64 key used to encrypt
        EXTEND in the ntor protocol

      * **or_addresses** (*list*) – ***** alternative for our
        address/or_port attributes, each entry is a tuple of the form
        (address (**str**), port (**int**), is_ipv6 (**bool**))

      * **family** (*list*) – ***** nicknames or fingerprints of
        declared family

      * **exit_policy** (*stem.exit_policy.MicroExitPolicy*) – *****
        relay’s exit policy

      * **exit_policy_v6** (*stem.exit_policy.MicroExitPolicy*) –
        ***** exit policy for IPv6

      * **identifiers** (*hash*) – mapping of key types (like
        rsa1024 or ed25519) to their base64 encoded identity, this is
        only used for collision prevention (ticket 11743)

      * **protocols** (*dict*) – mapping of protocols to their
        supported versions

      * **identifier** (*str*) – base64 encoded identity digest
        (**deprecated**, use identifiers instead)

      * **identifier_type** (*str*) – identity digest key type
        (**deprecated**, use identifiers instead)

   ***** attribute is required when we’re parsed with validation

   Changed in version 1.1.0: Added the identifier and identifier_type
   attributes.

   Changed in version 1.5.0: Added the identifiers attribute, and
   deprecated identifier and identifier_type since the field can now
   appear multiple times.

   Changed in version 1.6.0: Added the protocols attribute.

   Changed in version 1.8.0: Replaced our **digest** attribute with a
   much more flexible **digest()** method. Unfortunately I cannot do
   this in a backward compatible way because of the name conflict. The
   old digest had multiple problems (for instance, being hex rather
   than base64 encoded), so hopefully no one was using it. Very sorry
   if this causes trouble for anyone.

   TYPE_ANNOTATION_NAME = 'microdescriptor'

   classmethod content(attr=None, exclude=(), sign=False)

      Creates descriptor content with the given attributes. Mandatory
      fields are filled with dummy information unless data is
      supplied. This doesn’t yet create a valid signature.

      New in version 1.6.0.

      Parameters:
         * **attr** (*dict*) – keyword/value mappings to be included
           in the descriptor

         * **exclude** (*list*) – mandatory keywords to exclude from
           the descriptor, this results in an invalid descriptor

         * **sign** (*bool*) – includes cryptographic signatures and
           digests if True

      Returns:
         **str** with the content of a descriptor

      Raises:
         * **ImportError** if cryptography is unavailable and sign
           is True

         * **NotImplementedError** if not implemented for this
           descriptor type

   digest(hash_type='SHA256', encoding='BASE64')

      Digest of this microdescriptor. These are referenced by…

         * **Microdescriptor Consensus**

           * Referer: "RouterStatusEntryMicroV3" **digest**
             attribute

           * Format: **SHA256/BASE64**

      New in version 1.8.0.

      Parameters:
         * **hash_type** (*stem.descriptor.DigestHash*) – digest
           hashing algorithm

         * **encoding** (*stem.descriptor.DigestEncoding*) – digest
           encoding

      Returns:
         **hashlib.HASH** or **str** based on our encoding argument

   get_annotations

      Provides content that appeared prior to the descriptor. If this
      comes from the cached-microdescs then this commonly contains
      content like…

         @last-listed 2013-02-24 00:18:30

      Returns:
         **dict** with the key/value pairs in our annotations

   get_annotation_lines()

      Provides the lines of content that appeared prior to the
      descriptor. This is the same as the "get_annotations()" results,
      but with the unparsed lines and ordering retained.

      Returns:
         **list** with the lines of annotation that came before this
         descriptor
