Magic Folder: usability issues with 'tahoe magic-folder join'

[daira]

While manually testing Magic Folder, I ran the commands for Alice to create+join a folder, and to invite Bob. Then I accidentally had Alice use Bob's invite code to join again. This didn't cause an error; it just overwrote Alice's private/magic_folder_dircap and [magic_folder]local.directory entry.

This is an easy mistake to make and could cause data loss. Alice has lost her write cap to her DMD, and there is no way to get it back (only a read cap to that directory is linked from the collective directory). Also, Alice's magic folder db will be inconsistent with the DMD that she is now using.

The above problem is easy to fix by making it an error for a client to join a magic folder when it has one already configured. (Perhaps a tahoe magic-folder leave command could be added; this would disable magic folder and also delete the magic folder db.)

A related but trickier problem is that if the invite code is used twice, then two clients will be writing to the same DMD. There's no way to enforce that an invite code is single-use, because join is a strictly local operation that has no side effects on the collective directory. This has some advantages --if you lose state but retain the invite code then you can re-join-- but is also a little error-prone.

[dawuud]

I created a simple "leave" command... and taught the join command to only join if not already joined: ​https://github.com/david415/tahoe-lafs/tree/2568.make-join-useable.0

Please review.

[dawuud]

A missing feature from the above mentioned changeset is; the leave command must remove the magic-folder configuration section from the tahoe.cfg file.

Is there a set of helper functions for dealing with .cfg configuration files?

[dawuud]

teach leave to remove magic_folder section of config:

​https://github.com/david415/tahoe-lafs/tree/2568.make-join-useable.0 ​https://github.com/david415/tahoe-lafs/commit/52d730335bc2a60b1896ffb0b33efc8f2e6e7ed7

[daira]

Reviewing.

[dawuud]

i added a basic unit test for the "leave" command:

​https://github.com/david415/tahoe-lafs/tree/2568.make-join-useable.1 ​https://github.com/david415/tahoe-lafs/commit/3bdee00177691688bb81df0ac9ef0621fe6264d6

[dawuud]

added more join + leave unit tests in the same dev branch. These test might be sufficient. Review needed.

[dawuud]

i've made the corrections daira specified in this review: ​https://github.com/david415/tahoe-lafs/commit/63eec3bd871124a798b401ef0fc1ccc173299d60#commitcomment-14796066

changes pushed to my dev branch here: ​https://github.com/david415/tahoe-lafs/tree/2495.use-config-parser.0

please review

[dawuud]

use safe config parser: ​https://github.com/tahoe-lafs/tahoe-lafs/pull/208

[daira]

Replying to dawuud:

added more join + leave unit tests in the same dev branch. These test might be sufficient. Review needed.

LGTM modulo comments on the commits in ​https://github.com/tahoe-lafs/tahoe-lafs/compare/2568.make-join-useable.1...david415:2568.make-join-useable.1.

[dawuud]

more fixes in my dev branch: ​https://github.com/david415/tahoe-lafs/tree/2568.make-join-useable.1

please review added this pull request ​https://github.com/tahoe-lafs/tahoe-lafs/pull/214

[daira]

Please rebase the branch onto 2438.magic-folder-stable.5 and open a new PR.

[dawuud]

ok here's the new pull request ​https://github.com/tahoe-lafs/tahoe-lafs/pull/217

[daira]

Pushed to 2438.magic-folder-stable.5.wip .

[daira]

Pushed to 2438.magic-folder-stable.5 .

[Brian Warner <warner@…>]

In cd1c1667/trunk:

Improve the error reporting for 'tahoe magic-folder join/leave'. refs #2568

Signed-off-by: Daira Hopwood <daira@…>