Client.init_tempdir clobbers global state in an annoying way

[exarkun]

    def init_tempdir(self):
        """
        Initialize/create a directory for temporary files.
        """
        tempdir_config = self.config.get_config("node", "tempdir", "tmp")
        if isinstance(tempdir_config, bytes):
            tempdir_config = tempdir_config.decode('utf-8')
        tempdir = self.config.get_config_path(tempdir_config)
        if not os.path.exists(tempdir):
            fileutil.make_dirs(tempdir)
        tempfile.tempdir = tempdir

This makes it impossible to have two Client instances in one process that are truly independent of each other. The last one to init will make all the rest share its temporary directory!

In the past this has caused a lot of problem for the test suite when the mutation doesn't get cleaned up. Some parts of the test suite nest more and more deeply into node temp dirs. Sometimes this blows up the OS path length limits. Other times it's just confusing. Most recently for ticket:2916 one test leaked a *unicode* value into tempfile.tempdir and broke some subsequent tests which suddenly got unicode temp directories instead of bytes temp directories.

The explanatory comment:

        # this should cause twisted.web.http (which uses
        # tempfile.TemporaryFile) to put large request bodies in the given
        # directory. Without this, the default temp dir is usually /tmp/,
        # which is frequently too small.

makes it seem as though this is *only* for Twisted Web intermediate files. We can fix these in a better way. Request.gotLength and Site.getContentFile both give us interfaces to control this behavior in a way that's localized to a single client.

[exarkun]

Duplicate of ​https://tahoe-lafs.org/trac/tahoe-lafs/ticket/1549#comment:5

[GitHub <noreply@…>]

In 152c04e/trunk:

Merge pull request #902 from tahoe-lafs/3512.localized-tempdir

Per-node web temp directory

Fixes: ticket:3512