Add --print-uri option to "tahoe backup" to dump resulting backup URI

[amontero]

When I do [scripted] backups to my grid, I would like to collect the resulting backup root URI to a file. I've added a "--printcap" option to "tahoe backup" to do it and works good, so far.

Off by default for backwards compatibility. Comes to mind someone using "tahoe backup" from a script piping the output to a file and mailing it. Other than this, looks like an trivial addition.

Code is at: ​https://github.com/tahoe-lafs/tahoe-lafs/pull/76

[amontero]

Also you can accomplish David Sarah's case at ticket:835#10 with this one-liner:

$ tahoe backup --ignore-timestamps --printcap ~/Documents/ `tahoe mkdir`

The mkdir'ed directory URI is completely ignored, we will just keep the --printcap'ed URI as the *immutable* backup root.

[markberger]

+1

It might be good to add this option to the docs in frontends/CLI.rst.

[amontero]

Also a doubt: Better to print the URI alone with no surrounding text (as it's done in "tahoe put" or "tahoe mkdir")? If there was a --quiet option it would make sense, but printed along the backup summary, I think it's not worth it.

[daira]

Replying to amontero:

Also a doubt: Better to print the URI alone with no surrounding text (as it's done in "tahoe put" or "tahoe mkdir")? If there was a --quiet option it would make sense, but printed along the backup summary, I think it's not worth it.

Yes, that's a problem for use in scripts. Maybe print the URI alone on stdout, and the backup summary on stderr when --printcap is used?

[amontero]

Great idea, +1. Also, it's low hanging fruit :)

Done it, stripped the "Resulting backup..." string. Sample console output below.

 4 files uploaded (0 reused), 0 files skipped, 0 directories created (1 reused), 0 directories skipped
 backup done, elapsed time: 0:00:18
URI:DIR2-CHK:35ge[...]3gze:rij[...]nka:1:2:1074

It's OK to also redirect the more verbose messages to stderr?

[amontero]

I mean this one:

            if self.verbosity >= 2:
                print >>stdout, (" %d files checked, %d directories checked"
                                 % (self.files_checked,
                                    self.directories_checked))

[daira]

Yes.

[amontero]

As discussed in IRC:

• Renamed --printcap to --print-uri
• Tentatively adding -U as option shortcut (-u conflicts with --node-url)
• All verbosity messages previously sent to stdout now are sent to stderr. Only resulting backup URI goes to stdout.

Updated the pull request accordingly for review.

Also, I proposed Daira to make --print-uri the default behavior to make it consistent with "tahoe put" and "tahoe mkdir". However, this could be a security issue for existing scripts. Needs further discussion.

[remyroy]

I'll review this patch/pull request.

[remyroy]

Great code so far. I feel this would be quite useful for scripting backups.

There is still 2 failing backup related tests from this patch/pull request. The cli--tahoe-backup--dump-backup-dircap-stdout--tests branch from ​https://github.com/pataquets/tahoe-lafs/ seems to have some attempt at fixing those failing tests but they are still present.

There should also be an additional test in allmydata.test.test_cli.Backup to test this new command option.

Reassigning back to amontero for patch changes.

[daira]

This could potentially get into 1.11 if the tests were fixed, but the core developers will be focussing on other things, so that depends on amontero.