Fake Git Server (FGS)

FGS is actually not a fake at all. It is a real web server that serves real Git repositories them over HTTP. FGS wraps around the vanilla git http-backend subcommand that comes with Git, calling it as a CGI executable. It supports both read (e.g., git clone, git fetch) and write (e.g., git push) operations against it.

FGS is used for integration tests. See TestClonerefs for an example.

Usage in Integration Testing

The fakegitserver.go file is built automatically by hack/prowimagebuilder, and we deploy it to the KIND cluster. Inside the cluster, it accepts web traffic at the endpoint http://fakegitserver.default (http://localhost/fakegitserver from outside of the KIND cluster).

There are 2 routes:

• /repo/<REPO_NAME>: endpoint for Git clients to interact (git clone, git fetch, git push). E.g., git clone http://fakegitserver.default/repo/foo. Internally, FGS serves all Git repo folders under -git-repos-parent-dir on disk and serves them for the /repo route with the git-http-backend CGI script.
• POST /setup-repo: endpoint for creating new Git repos on the server; you just need to send a JSON payload like this:

{
  "name": "foo",
  "overwrite": true,
  "script": "echo hello world > README; git add README; git commit -m update"
}

Here is a cURL example:

# mkFoo is a plaintext file containing the JSON from above.
$ curl http://localhost/fakegitserver/setup-repo -d @mkFoo
commit c1e4e5bb8ba0e5b16147450a75347a27e5980222
Author: abc <d@e.f>
Date:   Thu May 19 12:34:56 2022 +0000

    update

Notice how the server responds with a git log output of the just-created repo to ease debugging in case repos are not created the way you expect them to be created.

During integration tests, each test creates repo(s) using the /setup-repo endpoint as above. Care must be taken to not reuse the same repository name, as the test cases (e.g., the test cases in TestClonerefs) all run in parallel and can clobber each other’s repo creation setp.

Allowing Push Access

Although this is not (yet) used in tests, push access is enabled for all served repos. This is achieved by setting the http.receivepack Git configuration option to true for each repo found under -git-repos-parent-dir. This is because the git http-backend script does not by default allow anonymous push access unless the aforementioned option is set to true on a per-repo basis.

Allowing Fetching of Commit SHAs

By default the CGI script will only serve references that are “advertised” (such as those references under refs/heads/* or refs/pull/*/head). However, FGS also sets the uploadpack.allowAnySHA1InWant option to true to allow Git clients (such as clonerefs) to fetch commits by their SHA.

Local Usage (for debugging)

FGS has 2 requirements:

1. the path to the local git binary installation, and
2. the path to a folder containing Git repositories to be served (can be an empty directory, or pre-populated).

By default port 8888 is used, although this can also be configured with -port.

Example:

$ go run fakegitserver.go -h
Usage of /tmp/go-build2317700172/b001/exe/fakegitserver:
  -git-binary git
        Path to the git binary. (default "/usr/bin/git")
  -git-repos-parent-dir string
        Path to the parent folder containing all Git repos to serve over HTTP. (default "/git-repo")
  -port int
        Port to listen on. (default 8888)

$ go run fakegitserver.go -git-repos-parent-dir <PATH_TO_REPOS> -git-binary <PATH_TO_GIT>
{"component":"unset","file":"/home/someuser/go/src/sigs.k8s.io/prow/prow/test/integration/fakegitserver/fakegitserver.go:111","func":"main.main","level":"info","msg":"Start server","severity":"info","time":"2022-05-22T20:31:38-07:00"}

In this example, http://localhost:8888 is the HTTP address of FGS:

# Clone "foo" repo, assuming it exists locally under `-git-repos-parent-dir`.
$ git clone http://localhost:8888/repo/foo
$ cd foo
$ git log # or any other arbitrary Git command
# ... do some Git operations
$ git push

That’s it!

Local Usage with Docker and Ko (for debugging)

It may be helpful to run FGS in a containerized environment for debugging. First install ko itself. Then cd to the fakegitserver folder (same folder as this README.md file), and run:

# First CD to the root of the repo, because the .ko.yaml configuration (unfortunately)
# depends on relative paths that can only work from the root of the repo.
$ cd ${PATH_TO_REPO_ROOT}
$ docker run -it --entrypoint=sh -p 8123:8888 $(ko build --local sigs.k8s.io/prow/prow/test/integration/fakegitserver)

The -p 8123:8888 allows you to talk to the containerized instance of fakegitserver over port 8123 on the host.

Custom Base Image

To use a custom base image for FGS, change the baseImageOverrides entry for fakegitserver in .ko.yaml like this:

baseImageOverrides:
  # ... other entries ...
  sigs.k8s.io/prow/prow/test/integration/fakegitserver: gcr.io/my/base/image:tag

If you want ko to pick up a local Docker image on your machine, rename the image to have a ko.local prefix. For example, like this:

baseImageOverrides:
  sigs.k8s.io/prow/prow/test/integration/fakegitserver: ko.local/my/base/image:tag