Parse messages sent by the svn 'commit-email.pl' trigger.

def parse(self, m, prefix=None):
        """Parse messages sent by the svn 'commit-email.pl' trigger.
        """

        # The mail is sent from the person doing the checkin. Assume that the
        # local username is enough to identify them (this assumes a one-server
        # cvs-over-rsh environment rather than the server-dirs-shared-over-NFS
        # model)
        name, addr = parseaddr(m["from"])
        if not addr:
            return None  # no From means this message isn't from svn
        at = addr.find("@")
        if at == -1:
            author = addr  # might still be useful
        else:
            author = addr[:at]

        # we take the time of receipt as the time of checkin. Not correct (it
        # depends upon the email latency), but it avoids the
        # out-of-order-changes issue. Also syncmail doesn't give us anything
        # better to work with, unless you count pulling the v1-vs-v2
        # timestamp out of the diffs, which would be ugly. TODO: Pulling the
        # 'Date:' header from the mail is a possibility, and
        # email.utils.parsedate_tz may be useful. It should be configurable,
        # however, because there are a lot of broken clocks out there.
        when = util.now()

        files = []
        comments = ""
        lines = list(body_line_iterator(m))
        rev = None
        while lines:
            line = lines.pop(0)

            # "Author: jmason"
            match = re.search(r"^Author: (\S+)", line)
            if match:
                author = match.group(1)

            # "New Revision: 105955"
            match = re.search(r"^New Revision: (\d+)", line)
            if match:
                rev = match.group(1)

            # possible TODO: use "Date: ..." data here instead of time of
            # commit message receipt, above. however, this timestamp is
            # specified *without* a timezone, in the server's local TZ, so to
            # be accurate buildbot would need a config setting to specify the
            # source server's expected TZ setting! messy.

            # this stanza ends with the "Log:"
            if (line == "Log:\n"):
                break

        # commit message is terminated by the file-listing section
        while lines:
            line = lines.pop(0)
            if line in ("Modified:\n", "Added:\n", "Removed:\n"):
                break
            comments += line
        comments = comments.rstrip() + "\n"

        while lines:
            line = lines.pop(0)
            if line == "\n":
                break
            if line.find("Modified:\n") == 0:
                continue            # ignore this line
            if line.find("Added:\n") == 0:
                continue            # ignore this line
            if line.find("Removed:\n") == 0:
                continue            # ignore this line
            line = line.strip()

            thesefiles = line.split(" ")
            for f in thesefiles:
                if prefix:
                    # insist that the file start with the prefix: we may get
                    # changes we don't care about too
                    if f.startswith(prefix):
                        f = f[len(prefix):]
                    else:
                        log.msg("ignored file from svn commit: prefix '%s' "
                                "does not match filename '%s'" % (prefix, f))
                        continue

                # TODO: figure out how new directories are described, set
                # .isdir
                files.append(f)

        if not files:
            log.msg("no matching files found, ignoring commit")
            return None

        return ('svn', dict(author=author, files=files, comments=comments,
                            when=when, revision=rev))