shown. Defaults to ``3``. If negative value is passed-in, it will be

          set to ``0`` instead.

        """

        # Negative context values make no sense, and will result in

        # errors. Ensure this does not happen.

        if context < 0:

            context = 0

        if hasattr(rev1, 'raw_id'):

            rev1 = getattr(rev1, 'raw_id')

        if hasattr(rev2, 'raw_id'):

            rev2 = getattr(rev2, 'raw_id')

        # Check if given revisions are present at repository (may raise

        # ChangesetDoesNotExistError)

        if rev1 != self.EMPTY_CHANGESET:

            self.get_changeset(rev1)

        self.get_changeset(rev2)

        if path:

            file_filter = mercurial.match.exact([safe_bytes(path)])

        else:

            file_filter = None

        return b''.join(mercurial.patch.diff(self._repo, rev1, rev2, match=file_filter,

                          opts=mercurial.mdiff.diffopts(git=True,

                                        showfunc=True,

                                        ignorews=ignore_whitespace,

                                        context=context)))

    @staticmethod

    def _check_url(url, repoui=None):

        r"""

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

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

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

        On failures it'll raise urllib2.HTTPError, exception is also thrown

        when the return code is non 200

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

        >>> MercurialRepository._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'>

        """

        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

            # When creating repos, _get_url will use file protocol for local paths

            return

        url = safe_bytes(url)

        if parsed_url.scheme == 'ssh':

            # in case of invalid uri or authentication issues, sshpeer will

            # throw an exception.

            mercurial.sshpeer.instance(repoui or mercurial.ui.ui(), url, False).lookup(b'tip')

            return

        url_obj = mercurial.util.url(url)

        test_uri, handlers = get_urllib_request_handlers(url_obj)

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

        cleaned_uri = str(url_obj)

        o = urllib.request.build_opener(*handlers)

        o.addheaders = [('Content-Type', 'application/mercurial-0.1'),

                        ('Accept', 'application/mercurial-0.1')]

        req = urllib.request.Request(

            "%s?%s" % (

                safe_str(test_uri),

                urllib.parse.urlencode({

                    'cmd': 'between',

                    'pairs': "%s-%s" % ('0' * 40, '0' * 40),

                })

            ))

        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 check if it's a proper hg repo

            try:

                mercurial.httppeer.instance(repoui or mercurial.ui.ui(), url, False).lookup(b'tip')

            except Exception as e:

                raise urllib.error.URLError(

                    "url [%s] does not look like an hg repo org_exc: %s"

                    % (cleaned_uri, e))

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

        """

        Function will check for mercurial repository in given path and return

        a localrepo object. If there is no repository in that path it will

        raise an exception unless ``create`` parameter is set to True - in

        that case repository would be created and returned.

        If ``src_url`` is given, would try to clone repository from the

        location at given clone_point. Additionally it'll make update to

        working copy accordingly to ``update_after_clone`` flag

        """

        try:

            if src_url:

                url = self._get_url(src_url)

                opts = {}

                if not update_after_clone:

                    opts.update({'noupdate': True})

                MercurialRepository._check_url(url, self.baseui)

                mercurial.commands.clone(self.baseui, safe_bytes(url), safe_bytes(self.path), **opts)

                # Don't try to create if we've already cloned repo

                create = False

            return mercurial.localrepo.instance(self.baseui, safe_bytes(self.path), create=create)

        except (mercurial.error.Abort, mercurial.error.RepoError) as err:

            if create:

                msg = "Cannot create repository at %s. Original error was %s" \

                    % (self.name, err)

            else:

                msg = "Not valid repository at %s. Original error was %s" \

                    % (self.name, err)

            raise RepositoryError(msg)

    @LazyProperty

    def in_memory_changeset(self):

        return inmemory.MercurialInMemoryChangeset(self)

    @LazyProperty

    def description(self):

        _desc = self._repo.ui.config(b'web', b'description', None, untrusted=True)

        return safe_str(_desc or b'unknown')