redirect from branch/.bzr

[David Allouche]

Some people try checking bzr branches from the branch page on launchpad.net. We should provide an appropriate redirection.

If $URL is the canonical URL of a Branch in Launchpad (e.g. https://launchpad.net/people/bzrk/+branch/bzrk/dev), then $URL/.bzr should redirect to $TARGET/.bzr.

$TARGET would be BranchView.url (the Branch.url if it is set, fallback to the supermirror URL).

It's unclear what should be the correct redirection code. 303 was suggested at first, but I think 302 would be more appropriate. See http://www.w3.org/Protocols/HTTP/HTRESP.html for the documentation of the HTTP status codes.

Two pagetests would be needed: one for redirection from $URL/.bzr where Branch.url is set. One for redirection of $URL/.bzr where Branch.url is NULL.

It would be nice to also implement an end-to-end test to check that bzr correctly handles the redirection, but that would be much more complicated.

[James Henstridge (jamesh)]

Before implementing this, bzr would need to handle redirects correctly as described in bug 36004.

If $LPBRANCHURL/.bzr redirects to $TARGET/.bzr and that branch is inside a repository, bzr needs to look for the repository relative to $TARGET rather than $LPBRANCHURL or it won't be able to use the branch.

[James Henstridge (jamesh)]

I had an idea of how we can implement this without signficant burden on the app server with current releases of bzr. We only need to serve 3 files without any HTTP redirects:

 * .bzr/branch-format with contents "Bazaar-NG meta directory, format 1"
 * .bzr/branch/format with contents "Bazaar-NG Branch Reference Format 1"
 * .bzr/branch/location with the HTTP URL of the branch.

I just tried putting this simple file structure on a local web server, and I was able to branch from it successfully. The recorded parent branch was the real Bazaar branch rather than the branch reference I created.

So this should result in the bzr client making 3 requests to https://launchpad.net when creating the branch, with all further requests going to http://bazaar.launchpad.net/.

[David Allouche (ddaa)]

I love this idea. It should be quite simple to implement and give us all we need. Also, all the db schema prerequisites are now present. That would be a great one-afternoon hack to put toghether.

[James Henstridge (jamesh)]

Did up a quick implementation of this last night.

[David Allouche (ddaa)]

got cherrypicked in production just today