We run a version control server for testing at vcs-test.golang.org.
The server can serve Bazaar, Fossil, Git, Mercurial, and Subversion repositories. The root of each repository is https://vcs-test.golang.org/VCS/REPONAME, where VCS is the version control system's command name (bzr for Bazaar, and so on), and REPONAME is the repository name.
To serve a particular repository, the server downloads gs://vcs-test/VCS/REPONAME.zip from Google Cloud Storage and unzips it into an empty directory. The result should be a valid repository directory for the given version control system. If the needed format of the zip file is unclear, download and inspect gs://vcs-test/VCS/hello.zip from https://vcs-test.storage.googleapis.com/VCS/hello.zip.
Google Cloud Storage imposes a default Cache-Control policy of 3600 seconds for publicly-readable objects; for instructions to disable caching per object, see gsutil setmeta. vcweb itself may serve stale data for up to five minutes after a zip file is updated. To force a rescan of Google Cloud Storage, fetch https://vcs-test.golang.org/VCS/REPONAME?vcweb-force-reload=1.
The URL space https://vcs-test.golang.org/go/NAME is served by static files, fetched from gs://vcs-test/go/NAME.zip. The main use for static files is to write redirect HTML. See gs://vcs-test/go/hello.zip for examples. Note that because the server uses http.DetectContentType to deduce the content type from file data, it is not necessary to name HTML files with a .html suffix.
The server fetches an HTTPS certificate on demand from Let's Encrypt, using golang.org/x/crypto/acme/autocert. It caches the certificates in gs://vcs-test-autocert using golang.org/x/build/autocertcache.