This adds Node._create_tub(), which knows how to make a Tub with all the
right options and connection handlers that were specified in
tahoe.cfg (the connection handlers are disabled for now, but they'll get
implemented soon).
The new Node.create_main_tub() calls it. This main Tub is used:
* to connect to the Introducer
* to host the Helper (if enabled)
* to host the Storage Server (if enabled)
Node._create_tub() is also passed into the StorageFarmBroker, which
passes it into each NativeStorageServer, to create the (separate) Tub
for each server connection. _create_tub knows about the options, and
NativeStorageServer can override the connection handlers. This way we
don't need to pass tub options or default handlers into Client,
StorageFarmBroker, or NativeStorageServer.
A number of tests create NativeStorageServer objects: these were updated
to match the new arguments. test_storage_client was simplified because
we no longer need to mock out the Tub() constructor.
Many of the test cases would exercise two copies of each file: one with
k=3/N=10, and a second with k=127/N=255 (255 being the maximum supported
by zfec).
Large number of shares increases the overhead of the testing apparatus,
which is pushing those shares to lots of local servers.
I don't think the "max_shares" case is necessary, and it takes forever.
Because of it, "mutable.Update" was consuming 15% of the total test
runtime, and a third of that was just a single
function (test_replace_locations_max_shares, now deleted). On a
Raspberry Pi 3 (our "slow computer" benchmark), including branch
coverage, this one class took 42 minutes to complete, and requires
disabling a bunch of timeouts to finish at all.
The total number of shares in a file ("N") affects one thing: the
width (and thus height) of the share hash tree. This should be exercised
in test_hashtree.
The number of required shares ("k") affects one thing: the segment size
must be a multiple of k. I don't think we need to exercise this, but if
so, it could be exercised by a few small values for k, rather than 127.
Removing the max_shares cases saves 82% of the mutable.update
runtime (on top of the previous three-segment fix), reducing it from 64s
to 11.3s on my laptop.
