This is probably the cause of the very rare "loss of progress" bug. This is tested by unit tests. A recent patch changed this to errback instead of losing progress, and now this patch is changing it again to return a short read instead of errbacking. Returning a short read is what the uploader (in encode.py) is expecting, when it is reading the last block of the ciphertext, which might be shorter than the other blocks.
A test failed on draco (MacPPC) because it took 49 seconds to get around to running the test, and the node had already stopped itself when the hotline file was 40 seconds old.
It is currently hardcoded in setup.py to be 'allmydata-tahoe'. Ticket #556 is to make it configurable by a runtime command-line argument to setup.py: "--appname=foo", but I suddenly wondered if we really wanted that and at the same time realized that we don't need that for tahoe-1.3.0 release, so this patch just hardcodes it in setup.py.
setup.py inspects a file named 'src/allmydata/_appname.py' and assert that it contains the string "__appname__ = 'allmydata-tahoe'", and creates it if it isn't already present. src/allmydata/__init__.py import _appname and reads __appname__ from it. The rest of the Python code imports allmydata and inspects "allmydata.__appname__", although actually every use it uses "allmydata.__full_version__" instead, where "allmydata.__full_version__" is created in src/allmydata/__init__.py to be:
__full_version__ = __appname + '-' + str(__version__).
All the code that emits an "application version string" when describing what version of a protocol it supports (introducer server, storage server, upload helper), or when describing itself in general (introducer client), usese allmydata.__full_version__.
This fixes ticket #556 at least well enough for tahoe-1.3.0 release.
(There is a bug in the current DownUpConnector which can cause it to give more bytes than you asked for on one request, and then less on the next, effectively shifting some of the bytes to an earlier request, but I think this bug never gets triggered in practice.)
Obviously requiring the code under test to perform within some limit isn't very meaningful if we raise the limit whenever the test goes outside of it.
But I still don't want to remove the test code which measures how many writes (and, elsewhere, how many reads) a client does in order to fulfill these duties.
Let this number -- now 20 -- stand as an approximation of the inefficiency of our code divided by my mental model of how many operations are actually optimal for these duties.
