[tahoe-lafs-trac-stream] [Tahoe-LAFS] #2533: magic-folder CLI parsing error

[Tahoe-LAFS]

#2533: magic-folder CLI parsing error
----------------------------------------+---------------------------
 Reporter:  warner                      |          Owner:  daira
     Type:  defect                      |         Status:  new
 Priority:  normal                      |      Milestone:  undecided
Component:  code-frontend-magic-folder  |        Version:  1.10.1
 Keywords:                              |  Launchpad Bug:
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 In a demo today, Zooko tried to join a magic-folder instance with the
 following (incorrect) command:

 {{{
 % tahoe magic-folder join
 "URI:DIR2-RO:geydj2tsjteoxiezxwxmff46jq:nfczfkluafttupukia2umqthm2mqh3lu5olouby4nxcdcc36s3fa+URI:DIR2:yy5l52jcuj7k5khumae7stbtry:feo2jnoqcnhktoyggewibqjbr26unjajnudogaa2sbxhafnlvidq"
 --basedir=c
 }}}

 This is wrong for two reasons:

 * the `--basedir` option needs to come between `magic-folder` and `join`,
 rather than at the end of the command
 * it lacks the `LOCALDIR` positional argument, which is supposed to come
 after the `INVITATION-CODE` pair-of-dircaps

 What happened was even worse:

 * the command modified tahoe.cfg in the default basedir (`~/.tahoe/`),
 rather than the intended `./c`
 * the command recorded `--basedir=c` as the name of the directory to sync.
 As in `./--basedir=c/files`.

 I'm somewhat surprised that twisted.python.usage (the argument parser) was
 willing to accept a `--` -prefixed string as a positional argument.. it's
 a legal (if ill-advised) pathname, so it makes sense that it "worked", but
 leads to bad failure modes like this one. Some argument parsers (maybe
 argparse?) remove all `--`-prefixed strings first, attempt to parser them
 as options, then use only the remaining arguments to fill the positional
 slots. Such a parser would reject that command twice: once for having no
 --basedir option (at that level of the subcommands), and again for failing
 to have a positional argument at the expected location (since
 `--basedir=c` would have been removed by that point).

 I'm not sure what tahoe can do about this, but it's tempting to make a
 rule that filenames must start with one of `[a-zA-Z0-9\.\/]`, or at least
 reject filenames that start with - or -- (and remind users to say `./-foo`
 if they really want that).

--
Ticket URL: <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/2533>
Tahoe-LAFS <https://Tahoe-LAFS.org>
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