One of the things we’ve been working on for Launchpad is good integration with Bazaar. Launchpad provides a way to register or host Bazaar branches, and nominate a Bazaar branch as representing a particular product series.
For each registered branch, there is a branch information page. This leads to a bit of confusion since Bazaar uses URLs to identify branches, so people try running bzr branch on a branch information page. We also get people trying to branch the product or product series pages.
There were two ways we could address this problem: (1) do more to encourage people not to do this, or (2) make bzr branch do what the user meant it to do. The second option is the more user friendly, so that’s what we chose. This just left the problem of how to implement it efficiently.
The obvious way to get this to work is with a simple HTTP redirect for files under the .bzr/ directory. Unfortunately this would result in Bazaar hitting the Launchpad webapp for every file in the branch which is not desirable (each request results in a number of database accesses, which would add unnecessary load to the system). There is a Bazaar bug about improving this so that it would use the new location after the first redirect. This bug was the main reason for not implementing the feature previously.
While playing around with things a bit, I realised that Bazaar already had the features needed to implement the redirects and they have been there since 0.8.
In Bazaar 0.8, the concept of a lightweight checkout was introduced. This is just a working tree plus a reference to a branch stored elsewhere. You can perform most operations on the branch from the checkout directory that you can do from the real branch directory. So what happens if you publish the “branch reference” part of a lightweight checkout on the web? It turns out that they work fine, so that’s what I used for launchpad.net.
So with the change in place, the following commands will all give you a copy of the Bazaar webserve plugin:
bzr branch http://bazaar.launchpad.net/~bzr/bzr-webserve/webserve-dev bzr branch https://launchpad.net/people/bzr/+branch/bzr-webserve/webserve-dev bzr branch https://launchpad.net/products/bzr-webserve/trunk bzr branch https://launchpad.net/products/bzr-webserve
Furthermore, they will all record the http://bazaar.launchpad.net/ URL as the parent branch, so future bzr pull commands will go directly to the branch.