remote-helpers: add testgit helper

Currently the remote helper infrastructure is only used by the curl
helper, which does not give a good impression of how remote helpers
can be used to interact with foreign repositories. Since implementing
such a helper is non-trivial it would be good to have at least one
easy-to-follow example demonstrating how to implement a helper that
interacts with a foreign vcs using fast-import/fast-export.

The testgit helper can be used to interact with remote git
repositories by prefixing the url with "testgit::".

Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-remote-testgit.py

@@ -0,0 +1,233 @@
+#!/usr/bin/env python
+
+import hashlib
+import sys
+
+from git_remote_helpers.util import die, debug, warn
+from git_remote_helpers.git.repo import GitRepo
+from git_remote_helpers.git.exporter import GitExporter
+from git_remote_helpers.git.importer import GitImporter
+from git_remote_helpers.git.non_local import NonLocalGit
+
+def get_repo(alias, url):
+    """Returns a git repository object initialized for usage.
+    """
+
+    repo = GitRepo(url)
+    repo.get_revs()
+    repo.get_head()
+
+    hasher = hashlib.sha1()
+    hasher.update(repo.path)
+    repo.hash = hasher.hexdigest()
+
+    repo.get_base_path = lambda base: os.path.join(
+        base, 'info', 'fast-import', repo.hash)
+
+    prefix = 'refs/testgit/%s/' % alias
+    debug("prefix: '%s'", prefix)
+
+    repo.gitdir = ""
+    repo.alias = alias
+    repo.prefix = prefix
+
+    repo.exporter = GitExporter(repo)
+    repo.importer = GitImporter(repo)
+    repo.non_local = NonLocalGit(repo)
+
+    return repo
+
+
+def local_repo(repo, path):
+    """Returns a git repository object initalized for usage.
+    """
+
+    local = GitRepo(path)
+
+    local.non_local = None
+    local.gitdir = repo.gitdir
+    local.alias = repo.alias
+    local.prefix = repo.prefix
+    local.hash = repo.hash
+    local.get_base_path = repo.get_base_path
+    local.exporter = GitExporter(local)
+    local.importer = GitImporter(local)
+
+    return local
+
+
+def do_capabilities(repo, args):
+    """Prints the supported capabilities.
+    """
+
+    print "import"
+    print "export"
+    print "gitdir"
+    print "refspec refs/heads/*:%s*" % repo.prefix
+
+    print # end capabilities
+
+
+def do_list(repo, args):
+    """Lists all known references.
+
+    Bug: This will always set the remote head to master for non-local
+    repositories, since we have no way of determining what the remote
+    head is at clone time.
+    """
+
+    for ref in repo.revs:
+        debug("? refs/heads/%s", ref)
+        print "? refs/heads/%s" % ref
+
+    if repo.head:
+        debug("@refs/heads/%s HEAD" % repo.head)
+        print "@refs/heads/%s HEAD" % repo.head
+    else:
+        debug("@refs/heads/master HEAD")
+        print "@refs/heads/master HEAD"
+
+    print # end list
+
+
+def update_local_repo(repo):
+    """Updates (or clones) a local repo.
+    """
+
+    if repo.local:
+        return repo
+
+    path = repo.non_local.clone(repo.gitdir)
+    repo.non_local.update(repo.gitdir)
+    repo = local_repo(repo, path)
+    return repo
+
+
+def do_import(repo, args):
+    """Exports a fast-import stream from testgit for git to import.
+    """
+
+    if len(args) != 1:
+        die("Import needs exactly one ref")
+
+    if not repo.gitdir:
+        die("Need gitdir to import")
+
+    repo = update_local_repo(repo)
+    repo.exporter.export_repo(repo.gitdir)
+
+
+def do_export(repo, args):
+    """Imports a fast-import stream from git to testgit.
+    """
+
+    if not repo.gitdir:
+        die("Need gitdir to export")
+
+    dirname = repo.get_base_path(repo.gitdir)
+
+    if not os.path.exists(dirname):
+        os.makedirs(dirname)
+
+    path = os.path.join(dirname, 'testgit.marks')
+    print path
+    print path if os.path.exists(path) else ""
+    sys.stdout.flush()
+
+    update_local_repo(repo)
+    repo.importer.do_import(repo.gitdir)
+    repo.non_local.push(repo.gitdir)
+
+
+def do_gitdir(repo, args):
+    """Stores the location of the gitdir.
+    """
+
+    if not args:
+        die("gitdir needs an argument")
+
+    repo.gitdir = ' '.join(args)
+
+
+COMMANDS = {
+    'capabilities': do_capabilities,
+    'list': do_list,
+    'import': do_import,
+    'export': do_export,
+    'gitdir': do_gitdir,
+}
+
+
+def sanitize(value):
+    """Cleans up the url.
+    """
+
+    if value.startswith('testgit::'):
+        value = value[9:]
+
+    return value
+
+
+def read_one_line(repo):
+    """Reads and processes one command.
+    """
+
+    line = sys.stdin.readline()
+
+    cmdline = line
+
+    if not cmdline:
+        warn("Unexpected EOF")
+        return False
+
+    cmdline = cmdline.strip().split()
+    if not cmdline:
+        # Blank line means we're about to quit
+        return False
+
+    cmd = cmdline.pop(0)
+    debug("Got command '%s' with args '%s'", cmd, ' '.join(cmdline))
+
+    if cmd not in COMMANDS:
+        die("Unknown command, %s", cmd)
+
+    func = COMMANDS[cmd]
+    func(repo, cmdline)
+    sys.stdout.flush()
+
+    return True
+
+
+def main(args):
+    """Starts a new remote helper for the specified repository.
+    """
+
+    if len(args) != 3:
+        die("Expecting exactly three arguments.")
+        sys.exit(1)
+
+    if os.getenv("GIT_DEBUG_TESTGIT"):
+        import git_remote_helpers.util
+        git_remote_helpers.util.DEBUG = True
+
+    alias = sanitize(args[1])
+    url = sanitize(args[2])
+
+    if not alias.isalnum():
+        warn("non-alnum alias '%s'", alias)
+        alias = "tmp"
+
+    args[1] = alias
+    args[2] = url
+
+    repo = get_repo(alias, url)
+
+    debug("Got arguments %s", args[1:])
+
+    more = True
+
+    while (more):
+        more = read_one_line(repo)
+
+if __name__ == '__main__':
+    sys.exit(main(sys.argv))