the windows (cygwin) buildslave has been failing the key generator test
it turns out that the time check on whether to refill the pool, and the
reactor, are interacting such that when the maybe_refill_pool call posted
on the reactor fires, the test on whether to fill the pool fails.
this adds a loop in the failure case to retry each 1s until it is time
to refill the pool, thus mitigating this timing accuracy problem on
windows.
previously there was an edge case in the timing of expected behaviour
of the key_generator (w.r.t. the refresh delay and twisted/foolscap
delivery). if it took >6s for a key to be generated, then it was
possible for the pool refresh delay to transpire _during_ the
synchronous creation of a key in remote_get_rsa_key_pair. this could
lead to the timer elapsing during key creation and hence the pool
being refilled before control returned to the client.
this change ensures that the time window from a get key request
until the key gen reactor blocks to refill the pool is the time
since a request was answered, not since a request was asked.
this causes the behaviour to match expectations, as embodied in
test_keygen, even if the delay window is dropped to 0.1s
this cleans up KeyGenerator to be a service (a subservice of the
KeyGeneratorService as instantiated by the key-generator.tac app)
this means that the timer which replenishes the keypool will be
shutdown cleanly when the service is stopped.
adds checks on the key_generator service and client into the system
test 'test_mutable' such that one of the nodes (clients[3]) uses
the key_generator service, and checks that mutable file creation
in that node, via a variety of means, are all consuming keys from
the key_generator.
this adds a new service to pre-generate RSA key pairs. This allows
the expensive (i.e. slow) key generation to be placed into a process
outside the node, so that the node's reactor will not block when it
needs a key pair, but instead can retrieve them from a pool of already
generated key pairs in the key-generator service.
it adds a tahoe create-key-generator command which initialises an
empty dir with a tahoe-key-generator.tac file which can then be run
via twistd. it stashes its .pem and portnum for furl stability and
writes the furl of the key gen service to key_generator.furl, also
printing it to stdout.
by placing a key_generator.furl file into the nodes config directory
(e.g. ~/.tahoe) a node will attempt to connect to such a service, and
will use that when creating mutable files (i.e. directories) whenever
possible. if the keygen service is unavailable, it will perform the
key generation locally instead, as before.
