@classmethod

    def _run_git_command(cls, cmd, cwd=None):

        """

        Runs given ``cmd`` as git command and returns output bytes in a tuple

        (stdout, stderr) ... or raise RepositoryError.

        :param cmd: git command to be executed

        :param cwd: passed directly to subprocess

        """

        # need to clean fix GIT_DIR !

        gitenv = dict(os.environ)

        gitenv.pop('GIT_DIR', None)

        gitenv['GIT_CONFIG_NOGLOBAL'] = '1'

        assert isinstance(cmd, list), cmd

        cmd = [settings.GIT_EXECUTABLE_PATH, '-c', 'core.quotepath=false'] + cmd

        try:

            p = subprocessio.SubprocessIOChunker(cmd, cwd=cwd, env=gitenv, shell=False)

        except (EnvironmentError, OSError) as err:

            # output from the failing process is in str(EnvironmentError)

            msg = ("Couldn't run git command %s.\n"

                   "Subprocess failed with '%s': %s\n" %

                   (cmd, type(err).__name__, err)

            ).strip()

            log.error(msg)

            raise RepositoryError(msg)

        try:

            stdout = b''.join(p.output)

            stderr = b''.join(p.error)

        finally:

            p.close()

        # TODO: introduce option to make commands fail if they have any stderr output?

        if stderr:

            log.debug('stderr from %s:\n%s', cmd, stderr)

        else:

            log.debug('stderr from %s: None', cmd)

        return stdout, stderr

    def run_git_command(self, cmd):

        """

        Runs given ``cmd`` as git command with cwd set to current repo.

        Returns stdout as unicode str ... or raise RepositoryError.

        """

        cwd = None

        if os.path.isdir(self.path):

            cwd = self.path

        stdout, _stderr = self._run_git_command(cmd, cwd=cwd)

        return safe_str(stdout)

    @staticmethod

    def _check_url(url):

        r"""

        Raise URLError if url doesn't seem like a valid safe Git URL. We

        only allow http, https, git, and ssh URLs.

        For http and https URLs, make a connection and probe to see if it is valid.

        >>> GitRepository._check_url('git://example.com/my%20fine repo')

        >>> GitRepository._check_url('http://example.com:65537/repo')

        Traceback (most recent call last):

        ...

        urllib.error.URLError: <urlopen error Error parsing URL: 'http://example.com:65537/repo'>

        >>> GitRepository._check_url('foo')

        Traceback (most recent call last):

        ...

        urllib.error.URLError: <urlopen error Unsupported protocol in URL 'foo'>

        >>> GitRepository._check_url('file:///repo')

        Traceback (most recent call last):

        ...

        urllib.error.URLError: <urlopen error Unsupported protocol in URL 'file:///repo'>

        >>> GitRepository._check_url('git+http://example.com/repo')

        Traceback (most recent call last):

        ...

        urllib.error.URLError: <urlopen error Unsupported protocol in URL 'git+http://example.com/repo'>

        >>> GitRepository._check_url('git://example.com/%09')

        Traceback (most recent call last):

        ...

        urllib.error.URLError: <urlopen error Invalid escape character in path: '%'>

        >>> GitRepository._check_url('git://example.com/%x00')

        Traceback (most recent call last):

        ...

        urllib.error.URLError: <urlopen error Invalid escape character in path: '%'>

        >>> GitRepository._check_url(r'git://example.com/\u0009')

        Traceback (most recent call last):

        ...

        urllib.error.URLError: <urlopen error Invalid escape character in path: '\'>

        >>> GitRepository._check_url(r'git://example.com/\t')

        Traceback (most recent call last):

        ...

        urllib.error.URLError: <urlopen error Invalid escape character in path: '\'>

        >>> GitRepository._check_url('git://example.com/\t')

        Traceback (most recent call last):

        ...

        urllib.error.URLError: <urlopen error Invalid whitespace character in path: '\t'>

        """

        try:

            parsed_url = urllib.parse.urlparse(url)

            parsed_url.port  # trigger netloc parsing which might raise ValueError

        except ValueError:

            raise urllib.error.URLError("Error parsing URL: %r" % url)

        # check first if it's not an local url

        if os.path.isabs(url) and os.path.isdir(url):

            return

        if parsed_url.scheme == 'git':

            # Mitigate problems elsewhere with incorrect handling of encoded paths.

            # Don't trust urllib.parse.unquote but be prepared for more flexible implementations elsewhere.

            # Space is the only allowed whitespace character - directly or % encoded. No other % or \ is allowed.

            for c in parsed_url.path.replace('%20', ' '):

                if c in '%\\':

                    raise urllib.error.URLError("Invalid escape character in path: '%s'" % c)

                if c.isspace() and c != ' ':

                    raise urllib.error.URLError("Invalid whitespace character in path: %r" % c)

            return

        if parsed_url.scheme not in ['http', 'https']:

            raise urllib.error.URLError("Unsupported protocol in URL %r" % url)

        url_obj = mercurial.util.url(safe_bytes(url))

        test_uri, handlers = get_urllib_request_handlers(url_obj)

        if not test_uri.endswith(b'info/refs'):

            test_uri = test_uri.rstrip(b'/') + b'/info/refs'

        url_obj.passwd = b'*****'

        cleaned_uri = str(url_obj)

        o = urllib.request.build_opener(*handlers)

        o.addheaders = [('User-Agent', 'git/1.7.8.0')]  # fake some git

        req = urllib.request.Request(

            "%s?%s" % (

                safe_str(test_uri),

                urllib.parse.urlencode({"service": 'git-upload-pack'})

            ))

        try:

            resp = o.open(req)

            if resp.code != 200:

                raise Exception('Return Code is not 200')

        except Exception as e:

            # means it cannot be cloned

            raise urllib.error.URLError("[%s] org_exc: %s" % (cleaned_uri, e))

        # now detect if it's proper git repo

        gitdata = resp.read()

        if b'service=git-upload-pack' not in gitdata:

            raise urllib.error.URLError(

                "url [%s] does not look like an git" % cleaned_uri)

    def _get_repo(self, create, src_url=None, update_after_clone=False,

                  bare=False):

        if create and os.path.exists(self.path):

            raise RepositoryError("Location already exist")

        if src_url and not create:

            raise RepositoryError("Create should be set to True if src_url is "

                                  "given (clone operation creates repository)")

        try:

            if create and src_url:

                GitRepository._check_url(src_url)

                self.clone(src_url, update_after_clone, bare)

                return Repo(self.path)

            elif create:

                os.makedirs(self.path)

                if bare:

                    return Repo.init_bare(self.path)

                else:

                    return Repo.init(self.path)

            else:

                return Repo(self.path)

        except (NotGitRepository, OSError) as err:

            raise RepositoryError(err)

    def _get_all_revisions(self):

        # we must check if this repo is not empty, since later command

        # fails if it is. And it's cheaper to ask than throw the subprocess

        # errors

        try:

            self._repo.head()

        except KeyError:

            return []

        rev_filter = settings.GIT_REV_FILTER

        cmd = ['rev-list', rev_filter, '--reverse', '--date-order']

        try:

            so = self.run_git_command(cmd)

        except RepositoryError:

            # Can be raised for empty repositories

            return []

        return so.splitlines()

    def _get_all_revisions2(self):

        # alternate implementation using dulwich

        includes = [ascii_str(sha) for key, (sha, type_) in self._parsed_refs.items()

                    if type_ != b'T']

        return [c.commit.id for c in self._repo.get_walker(include=includes)]

    def _get_revision(self, revision):

        """

        Given any revision identifier, returns a 40 char string with revision hash.

        """