This bug occurs because, in the function `bridgedb.Bridges.getConfigLine()`, the following lines determine ― when a request comes in ― the client's position in the hashring: ``` if not request: request = 'default' digest = get_hmac_fn('Order-Or-Addresses')(request) pos = long(digest[:8], 16) # lower 8 bytes -> long ``` Later on, in the same function, `pos` modulo the number of addresses this `Bridge` has, is used to index the collected/filtered addresses. Similarly, `pos` modulo the number of ports in the portlist is used to index the portlist: ``` # default ip, orport should get a chance at being selected if isinstance(self.ip, addressClass): addresses.insert(0,(self.ip, addr.PortList(self.orport))) if addresses: address,portlist = addresses[pos % len(addresses)] if isinstance(address, ipaddr.IPv6Address): ip = "[%s]"%address else: ip = "%s"%address orport = portlist[pos % len(portlist)] ``` Meaning that the fewer number of addresses/ports there are, the higher the chance that the `pos` will be modulo some small number which is a factor. For example, if there is only one address, this would be something like: ``` >>>from bridgedb import Bridges >>> digest = Bridges.get_hmac_fn('Order-Or-Addresses')('default') >>> pos = long(digest[:8], 16) >>> pos 3790090317L >>> pos % 1 0L ``` Which causes the following bug. What is extra strange is that the ValueError from trying to index these list-like things with a `0L` doesn't seem to occur on the addresses, only on the `orport = portlist[…` line. Though, it's also worth noting that the `'default'` value used in the hmac generation is usually a client's IP address, truncated to the /24. This means that this indexing-by-0L bug will occur rather indeterminately. ``` (bridgedb)∃!isisⒶwintermute:(fix/9462-refactor-netstatus-parsers_r9462C *+$=)~/code/torproject/bridgedb ∴ bridgedb Unhandled Error Traceback (most recent call last): File "/home/isis/.virtualenvs/bridgedb/local/lib/python2.7/site-packages/twisted/protocols/basic.py", line 571, in dataReceived why = self.lineReceived(line) File "/home/isis/.virtualenvs/bridgedb/local/lib/python2.7/site-packages/twisted/web/http.py", line 1619, in lineReceived self.allContentReceived() File "/home/isis/.virtualenvs/bridgedb/local/lib/python2.7/site-packages/twisted/web/http.py", line 1694, in allContentReceived req.requestReceived(command, path, version) File "/home/isis/.virtualenvs/bridgedb/local/lib/python2.7/site-packages/twisted/web/http.py", line 790, in requestReceived self.process() --- <exception caught here> --- File "/home/isis/.virtualenvs/bridgedb/local/lib/python2.7/site-packages/twisted/web/server.py", line 189, in process self.render(resrc) File "/home/isis/.virtualenvs/bridgedb/local/lib/python2.7/site-packages/twisted/web/server.py", line 238, in render body = resrc.render(self) File "/home/isis/.virtualenvs/bridgedb/local/lib/python2.7/site-packages/bridgedb-0.0.1_274_g594a221_dirty-py2.7.egg/bridgedb/HTTPServer.py", line 140, in render return self.getBridgeRequestAnswer(request) File "/home/isis/.virtualenvs/bridgedb/local/lib/python2.7/site-packages/bridgedb-0.0.1_274_g594a221_dirty-py2.7.egg/bridgedb/HTTPServer.py", line 218, in getBridgeRequestAnswer ) for b in bridges) File "/home/isis/.virtualenvs/bridgedb/local/lib/python2.7/site-packages/bridgedb-0.0.1_274_g594a221_dirty-py2.7.egg/bridgedb/HTTPServer.py", line 218, in <genexpr> ) for b in bridges) File "/home/isis/.virtualenvs/bridgedb/local/lib/python2.7/site-packages/bridgedb-0.0.1_274_g594a221_dirty-py2.7.egg/bridgedb/Bridges.py", line 192, in getConfigLine orport = portlist[pos % len(portlist)] File "/home/isis/.virtualenvs/bridgedb/local/lib/python2.7/site-packages/bridgedb-0.0.1_274_g594a221_dirty-py2.7.egg/bridgedb/parse/addr.py", line 372, in __getitem__ return portlist[portlist.index(port)] exceptions.ValueError: 0L is not in list ^C ```