1 files changed, 156 insertions, 0 deletions
diff --git a/git_mirror.py b/git_mirror.py
new file mode 100644
index 0000000..9b5b528
--- /dev/null
+++ b/git_mirror.py
@@ -0,0 +1,156 @@
+import sys, os, subprocess
+import configparser, itertools, json, re
+import email.mime.text, email.utils, smtplib
+
+class GitCommand:
+    def __getattr__(self, name):
+        def call(*args, capture_stderr = False, check = True):
+            '''If <capture_stderr>, return stderr merged with stdout. Otherwise, return stdout and forward stderr to our own.
+               If <check> is true, throw an exception of the process fails with non-zero exit code. Otherwise, do not.
+               In any case, return a pair of the captured output and the exit code.'''
+            cmd = ["git", name.replace('_', '-')] + list(args)
+            with subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.STDOUT if capture_stderr else None) as p:
+                (stdout, stderr) = p.communicate()
+                assert stderr is None
+                code = p.returncode
+                if check and code:
+                    raise Exception("Error running {0}: Non-zero exit code".format(cmd))
+            return (stdout.decode('utf-8').strip('\n'), code)
+        return call
+
+git = GitCommand()
+git_nullsha = 40*"0"
+
+def git_is_forced_update(oldsha, newsha):
+    out, code = git.merge_base("--is-ancestor", oldsha, newsha, check = False) # "Check if the first <commit> is an ancestor of the second <commit>"
+    assert not out
+    assert code in (0, 1)
+    return False if code == 0 else True # if oldsha is an ancestor of newsha, then this was a "good" (non-forced) update
+
+def read_config(fname, defSection = 'DEFAULT'):
+    '''Reads a config file that may have options outside of any section.'''
+    config = configparser.ConfigParser()
+    with open(fname) as file:
+        stream = itertools.chain(("["+defSection+"]\n",), file)
+        config.read_file(stream)
+    return config
+
+def send_mail(subject, text, receivers, sender='post+webhook@ralfj.de', replyTo=None):
+    assert isinstance(receivers, list)
+    if not len(receivers): return # nothing to do
+    # construct content
+    msg = email.mime.text.MIMEText(text.encode('UTF-8'), 'plain', 'UTF-8')
+    msg['Subject'] = subject
+    msg['Date'] = email.utils.formatdate(localtime=True)
+    msg['From'] = sender
+    msg['To'] = ', '.join(receivers)
+    if replyTo is not None:
+        msg['Reply-To'] = replyTo
+    # put into envelope and send
+    s = smtplib.SMTP('localhost')
+    s.sendmail(sender, receivers, msg.as_string())
+    s.quit()
+
+def get_github_payload():
+    '''Reeturn the github-style JSON encoded payload (as if we were called as a github webhook)'''
+    try:
+        data = sys.stdin.buffer.read()
+        data = json.loads(data.decode('utf-8'))
+        return data
+    except:
+        return {} # nothing read
+
+class Repo:
+    def __init__(self, name, conf):
+        '''Creates a repository from a section of the git-mirror configuration file'''
+        self.name = name
+        self.local = conf['local']
+        self.owner = conf['owner'] # email address to notify in case of problems
+        self.mirrors = {} # maps mirrors to their URLs
+        mirror_prefix = 'mirror-'
+        for name in filter(lambda s: s.startswith(mirror_prefix), conf.keys()):
+            mirror = name[len(mirror_prefix):]
+            self.mirrors[mirror] = conf[name]
+    
+    def mail_owner(self, msg):
+        send_mail("git-mirror {0}".format(self.name), msg, [self.owner])
+    
+    def find_mirror_by_url(self, match_urls):
+        for mirror, url in self.mirrors.items():
+            if url in match_urls:
+                return mirror
+        return None
+    
+    def update_mirrors(self, ref, oldsha, newsha, except_mirrors = [], suppress_stderr = False):
+        '''Update the <ref> from <oldsha> to <newsha> on all mirrors. The update must already have happened locally.'''
+        assert len(oldsha) == 40 and len(newsha) == 40, "These are not valid SHAs."
+        os.chdir(self.local)
+        # check for a forced update
+        is_forced = newsha != git_nullsha and oldsha != git_nullsha and git_is_forced_update(oldsha, newsha)
+        # tell all the mirrors
+        for mirror in self.mirrors:
+            if mirror in except_mirrors:
+                continue
+            # update this mirror
+            if is_forced:
+                # forcibly update ref remotely (someone already did a force push and hence accepted data loss)
+                git.push('--force', self.mirrors[mirror], newsha+":"+ref, capture_stderr = suppress_stderr)
+            else:
+                # nicely update ref remotely (this avoids data loss due to race conditions)
+                git.push(self.mirrors[mirror], newsha+":"+ref, capture_stderr = suppress_stderr)
+    
+    def update_ref_from_mirror(self, ref, oldsha, newsha, mirror, suppress_stderr = False):
+        '''Update the local version of this <ref> to what's currently on the given <mirror>. <oldsha> and <newsha> are checked. Then update all the other mirrors.'''
+        os.chdir(self.local)
+        url = self.mirrors[mirror]
+        # first check whether the remote really is at newsha
+        remote_state, code = git.ls_remote(url, ref)
+        if remote_state:
+            remote_sha = remote_state.split()[0]
+        else:
+            remote_sha = git_nullsha
+        assert newsha == remote_sha, "Someone lied about the new SHA, which should be {0}.".format(newsha)
+        # locally, we have to be at oldsha or newsha (the latter can happen if we already got this update, e.g. if it originated from us)
+        local_state, code = git.show_ref(ref, check=False)
+        if code == 0:
+            local_sha = local_state.split()[0]
+        else:
+            if len(local_state):
+                raise Exception("Something went wrong getting the local state of {0}.".format(ref))
+            local_sha = git_nullsha
+        assert local_sha in (oldsha, newsha), "Someone lied about the old SHA."
+        # if we are already at newsha locally, we also ran the local hooks, so we do not have to do anything
+        if local_sha == newsha:
+            return
+        # update local state from local_sha to newsha.
+        if newsha != git_nullsha:
+            # We *could* now fetch the remote ref and immediately update the local one. However, then we would have to
+            # decide whether we want to allow a force-update or not. Also, the ref could already have changed remotely,
+            # so that may update to some other commit.
+            # Instead, we just fetch without updating any local ref. If the remote side changed in such a way that
+            # <newsha> is not actually fetched, that's a race and will be noticed when updating the local ref.
+            git.fetch(url, ref, capture_stderr = suppress_stderr)
+            # now update the ref, checking the old value is still local_oldsha.
+            git.update_ref(ref, newsha, 40*"0" if local_sha is None else local_sha)
+        else:
+            # ref does not exist anymore. delete it.
+            assert local_sha != git_nullsha, "Why didn't we bail out earlier if there is nothing to do...?"
+            git.update_ref("-d", ref, local_sha) # this checks that the old value is still local_sha
+        # update all the mirrors
+        self.update_mirrors(ref, oldsha, newsha, [mirror], suppress_stderr)
+
+def find_repo_by_directory(repos, dir):
+    for (name, repo) in repos.items():
+        if dir == repo.local:
+            return name
+    return None
+
+def load_repos():
+    conffile = os.path.join(os.path.dirname(__file__), 'git-mirror.conf')
+    conf = read_config(conffile)
+    repos = {}
+    for name, section in conf.items():
+        if name != 'DEFAULT':
+            repos[name] = Repo(name, section)
+    return repos
+