launchpadblog

After a few weeks of development and testing, we are proud to finally announce that Git protocol v2 is available at Launchpad! But what are the improvements in the protocol itself, and how can you benefit from that?

The git v2 protocol was released a while ago, in May 2018, with the intent of simplifying git over HTTP transfer protocol, allowing extensibility of git capabilities, and reducing the network usage in some operations.

For the end user, the main clear benefit is the bandwidth reduction: in the previous version of the protocol, when one does a “git pull origin master”, for example, even if you have no new commits to fetch from the remote origin, git server would first “advertise” to the client all refs (branches and tags) available. In big repositories with hundreds or thousands of refs, this simple handshake operation could consume a lot of bandwidth and time to communicate a bunch of data that would potentially be discarded by the client after.

In the v2 protocol, this waste is no longer present: the client now has the ability to filter which refs it wants to know about before the server starts advertising it.

The v2 protocol is not the default on git clients yet, but if you are using a git version higher than 2.19, you can use v2: simply run git config --global protocol.version 2, and you will be using the most recent protocol version when communicating with servers that support this version. Including Launchpad, of course.

And even if you have repositories hosted in a server that is not yet compatible with v2, don’t worry: the git client is backward compatible. If the server does not support v2, git client should fall back gracefully to the previous version and everything should continue to work as expected. We hope you enjoy the new feature. And let us know if you have any feedback!

We’ve had Git hosting support in Launchpad for a few years now. One thing that some users asked for, particularly larger users such as the Ubuntu kernel team, was the ability to set up per-branch push permissions for their repositories. Today we rolled out the last piece of this work.

Launchpad’s default behaviour is that repository owners may push anything to their own repositories, including creating new branches, force-pushing (rewriting history), and deleting branches, while nobody else may push anything. Repository owners can now also choose to protect branches or tags, either individually or using wildcard rules. If a branch is protected, then by default repository owners can only create or push it but cannot force-push or delete; if a tag is protected, then by default repository owners can create it but cannot move or delete it.

You can also allow selected contributors to push to protected branches or tags, so if you’re collaborating with somebody on a branch and just want to be able to quickly pair-program via git push, or you want a merge robot to be able to land merge proposals in your repository without having to add it to the team that owns the repository and thus give it privileges it doesn’t need, then this feature may be for you.

There’s some initial documentation on our help site, and here’s a screenshot of a repository that’s been set up to give a contributor push access to a single branch:

Launchpad has had Git-to-Bazaar code imports since 2009, along with imports from a few other systems.  These form part of Launchpad’s original mission to keep track of free software, regardless of where it’s hosted.  They’re also very useful for automatically building other artifacts, such as source package recipes or snap packages, from code hosted elsewhere.  Unfortunately they’re quite complicated: they need to be able to do a full round-trip conversion of every revision from the other version control system, which has made it difficult to add support for Git features such as signed commits or submodules.  Once one of these features is present anywhere in the history of a branch, importing it to Bazaar becomes impossible.  This has been a headache for many users.

We can do better nowadays.  As of last year, we have direct Git hosting support in Launchpad, and we can already build snaps and recipes straight from Git, so we can fulfil our basic goal more robustly now with a lot less code.  So, Launchpad now supports Git-to-Git code imports, also known as Git mirroring.  You can use this to replace many uses of Git-to-Bazaar imports (note that there’s no translations integration yet, and of course you won’t be able to branch the resulting import using bzr).

See our Git documentation for more details.

We just rolled out a new feature for Launchpad’s Git repository hosting: Git-based merge proposals can now be linked to Launchpad bugs.  This can be done manually from the web UI for the merge proposal, but normally you should just mention the Launchpad bug in the commit message of one of the commits you want to merge.  The required commit message text to link to bugs #XXX and #YYY looks like this:

LP: #XXX, #YYY

This is the same form used for Launchpad bug references in debian/changelog files in source packages, and the general approach of mentioning bugs in commit messages is similar to that of various other hosting sites.

Bugs are not automatically closed when merge proposals land, because the policy for when that should happen varies from project to project: for example, projects often only close bugs when they make releases, or when their code is deployed to production sites.

Users familiar with Bazaar on Launchpad should note that the model for Git bug linking is slightly different: bugs are linked to merge proposals rather than to individual branches.  This difference is mainly because individual branches within a Git repository are often much more ephemeral than Bazaar branches.

Documentation is here, along with other details of Launchpad’s Git hosting.