How does the Gerrit server intercept commits. Looking for technical details

Question

I understand that Gerrit receives git commits (using the update hook perhaps), and write them on a fake ref somewhere until the peer review is done, but how exactly does that process work in terms of the technical implementation? And what Git commands are involved?

Answer 1

You might reference the magic reference refs/for/<branch ref> which is used by user when pushing new commits.

To create new changes for review, simply push to the project’s magical refs/for/'branch' ref using any Git client tool:

git push ssh://sshusername@hostname:29418/projectname HEAD:refs/for/branch

E.g. john.doe can use git push to upload new changes for the experimental branch of project kernel/common, hosted at the git.example.com Gerrit server:

git push ssh://[email protected]:29418/kernel/common HEAD:refs/for/experimental

Each new commit uploaded by the git push client will be converted into a change record on the server.
The remote ref refs/for/experimental is not actually created by Gerrit, even though the client’s status messages may say otherwise.

---

Technically, this is managed by the cmd-receive-pack.

Invoked by 'git push' and updates the project's repository with the information fed from the 'git push' end.

It is implemented by gerrit/sshd/commands/Receive.java, which receives change upload over SSH using the Git receive-pack protocol.