unicode error in _got_announcement at startup

[warner]

user "Vladislav" on the mailing list reported an exception when starting a node with an I2P-based client:

>  File "/home/vlad/.virtualenvs/tahoe/local/lib/python2.7/site-packages/foolscap/eventual.py",
> line 26, in _turn
>    cb(*args, **kwargs)
>  File "/home/vlad/tahoe-lafs/src/allmydata/storage_client.py", line 144, in _got_announcement
>    precondition(isinstance(key_s, str), key_s)
>  File "/home/vlad/tahoe-lafs/src/allmydata/util/assertutil.py", line 39, in precondition
>    raise AssertionError, "".join(msgbuf)
> exceptions.AssertionError: precondition: u'v0-myl4clrthvchbjn77vkojeadtaprngcubxuyjxcfimyb6irvdola' <type 'unicode'>

This looks like we're feeding a unicode key_s server-identifier into a function that really wants a string. There are two pathways into _got_announcement(): one is when the IntroducerClient receives a new announcement, the other is at startup when the IntroducerClient is reading the introducer_cache.yaml entries and delivering them as if they were real-time announcements.

I suspect that this is the second case, and we're missing code to string-ify the server-id values on the way in.

[warner]

patch in ​https://github.com/tahoe-lafs/tahoe-lafs/pull/329 , waiting for tests to run now

[Brian Warner <warner@…>]

In a1594df0/trunk:

introclient: only give ascii key_s to storagebroker

This was triggered when the initial Introducer connection failed, so the
node read the introducer_cache.yaml from disk. That always returns
unicode strings, and the StorageFarmBroker? insisted that it's
server-IDs (aka "key_s") were bytestrings.

The tests were extended to exercise the code that loads from disk and
delivers to the StorageFarmBroker?, and more preconditions were put in
place to catch this sort of thing earlier next time.

closes ticket:2817