git-svnserver

git-svnserver behaves like svnserve -t: it speaks the SVN protocol (ra_svn) over its standard input/output, the way a real svnserve does when invoked over ssh for a svn+ssh:// URL. Instead of a real Subversion repository, though, it serves the content of a Git repository's main branch, mapping each of its commits to one SVN revision — so existing SVN clients and tooling can browse a Git repository's history as if it were an SVN one.

It is built on top of github.com/cespedes/svn (the ra_svn protocol implementation) and github.com/go-git/go-git (reading the Git repository itself).

This is a work in progress. Only one branch — the repository's HEAD — is exposed, and only a subset of ra_svn is implemented so far. There is no write support yet (SVN clients see a read-only repository): that depends on github.com/cespedes/svn gaining commit support on the server side first.

Status

svn subcommand	Works?
info / ls / cat / log (including log -v)	✅
checkout / update, of a whole connected repository or a subdirectory	✅
diff of two repository revisions, or of a working copy against one, of a whole repository, a directory, or a single file (nested or not)	✅
switch, between two repository locations that don't share any recorded copy history (e.g. trunk and branches/foo, added independently) -- needs --ignore-ancestry for that reason	✅
update/switch against a "mixed-revision" working copy (part of it pinned to an older revision, e.g. via svn update -r)	❌ (rejected with a clear error)
commit and any other write operation	❌ (not implemented yet: needs commit support in github.com/cespedes/svn first)

log -v's changed-paths list does not detect renames/copies: it comes from a plain Git tree diff with no rename detection, so a rename shows up as a delete plus an add on two different paths, rather than a single "copied from" entry. For the same reason, svn switch between two locations always needs --ignore-ancestry: a real svn client otherwise refuses to switch unless the destination is recorded as a copy of (or otherwise historically related to) the source, which nothing here ever reports.

How revisions map to commits

SVN revisions are consecutive integers; Git history (even on a single branch) is a DAG. To bridge the two, each commit reached by following a branch's first-parent history from its tip is numbered in order, oldest first: revision 1 is the first commit, revision 2 the next one on that chain, and so on. Revision 0 is the (implicit) empty repository, before the first commit.

This mapping is cached in a file named svnserver-revmap, inside the repository's .git directory: it is created the first time the repository is served, and extended (or, if the branch's history was rewritten, e.g. by a rebase, fully rebuilt) every time it is served again and the branch has moved.

Locating the repository

Like a real svnserve -t invoked without -r (no jailed root), the repository to serve isn't given on the command line: it comes from the path component of the URL the connecting client sends during the protocol handshake (e.g. the /home/user/repo in svn+ssh://host/home/user/repo). git-svnserver walks up from that path looking for the first ancestor directory that is a valid Git repository, the same way a real svnserve looks for the first ancestor that is a valid SVN repository; anything below that root (e.g. trunk/sub in svn+ssh://host/home/user/repo/trunk/sub) is treated as a path inside the repository, not as part of locating it. At each ancestor, a .git-suffixed version of that same directory (e.g. repo.git alongside repo) is also tried, since a bare repository's directory conventionally has that suffix on disk, but spelling it out in every SVN URL would be an odd, very un-SVN-like thing to force on every client.

Usage

git-svnserver is meant to be invoked as an SSH tunnel command, exactly like svnserve -t:

ssh user@host git-svnserver -t

To try it out locally without SSH, svn's own tunnel mechanism can point straight at the built binary:

go build -o git-svnserver .

svn info \
  --config-option=config:tunnels:gitsvnserver=$PWD/git-svnserver \
  svn+gitsvnserver://localhost/absolute/path/to/some/git/repo

Development

go build ./...
go test ./...

If git and svn are installed, go test ./... also runs integration tests that create a temporary Git repository and run a real svn client against it (through the tunnel mechanism above, without any network involved); they're skipped cleanly otherwise.

License

MIT