git: update check for invalid URL characters to work with Python versions that include an attempt at fixing the very same problem

With changes like
https://github.com/python/cpython/commit/76cd81d60310d65d01f9d7b48a8985d8ab89c8b4
making it to Python 3.10 and being backported to previous Python versions, the
approach in a8a51a3bdb61 no longer works when combined with
urllib.parse.urlparse in d2f59de17bef: path will never contain the invalid
characters.

To catch this case anyway, add a new check to verify that the parsed URL can
roundtrip back to the original representation with urllib.parse.urlunparse .

The actual exception might vary, but one of them should always fire.

There is a risk that the new check will reject some URLs that somehow isn't
normalized. No such cases have been found yet.

kallithea/lib/vcs/backends/git/repository.py

@@ -1,819 +1,827 b''
 # -*- coding: utf-8 -*-
 """
     vcs.backends.git.repository
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
     Git repository implementation.
 
     :created_on: Apr 8, 2010
     :copyright: (c) 2010-2011 by Marcin Kuzminski, Lukasz Balcerzak.
 """
 
 import errno
 import logging
 import os
 import re
 import time
 import urllib.error
 import urllib.parse
 import urllib.request
 from collections import OrderedDict
 
 import mercurial.util  # import url as hg_url
 from dulwich.client import SubprocessGitClient
 from dulwich.config import ConfigFile
 from dulwich.objects import Tag
 from dulwich.repo import NotGitRepository, Repo
 from dulwich.server import update_server_info
 
 from kallithea.lib.vcs import subprocessio
 from kallithea.lib.vcs.backends.base import BaseRepository, CollectionGenerator
 from kallithea.lib.vcs.conf import settings
 from kallithea.lib.vcs.exceptions import (BranchDoesNotExistError, ChangesetDoesNotExistError, EmptyRepositoryError, RepositoryError, TagAlreadyExistError,
                                           TagDoesNotExistError)
 from kallithea.lib.vcs.utils import ascii_bytes, ascii_str, date_fromtimestamp, makedate, safe_bytes, safe_str
 from kallithea.lib.vcs.utils.helpers import get_urllib_request_handlers
 from kallithea.lib.vcs.utils.lazy import LazyProperty
 from kallithea.lib.vcs.utils.paths import abspath, get_user_home
 
 from . import changeset, inmemory, workdir
 
 
 SHA_PATTERN = re.compile(r'^([0-9a-fA-F]{12}|[0-9a-fA-F]{40})$')
 
 log = logging.getLogger(__name__)
 
 
 class GitRepository(BaseRepository):
     """
     Git repository backend.
     """
     DEFAULT_BRANCH_NAME = 'master'
     scm = 'git'
 
     def __init__(self, repo_path, create=False, src_url=None,
                  update_after_clone=False, bare=False, baseui=None):
         baseui  # unused
         self.path = abspath(repo_path)
         self.repo = self._get_repo(create, src_url, update_after_clone, bare)
         self.bare = self.repo.bare
 
     @property
     def _config_files(self):
         return [
             self.bare and abspath(self.path, 'config')
                       or abspath(self.path, '.git', 'config'),
              abspath(get_user_home(), '.gitconfig'),
          ]
 
     @property
     def _repo(self):
         return self.repo
 
     @property
     def head(self):
         try:
             return self._repo.head()
         except KeyError:
             return None
 
     @property
     def _empty(self):
         """
         Checks if repository is empty ie. without any changesets
         """
 
         try:
             self.revisions[0]
         except (KeyError, IndexError):
             return True
         return False
 
     @LazyProperty
     def revisions(self):
         """
         Returns list of revisions' ids, in ascending order.  Being lazy
         attribute allows external tools to inject shas from cache.
         """
         return self._get_all_revisions()
 
     @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 ...>
+
+        The failure above will be one of, depending on the level of WhatWG support:
         urllib.error.URLError: <urlopen error Invalid whitespace character in path: '\t'>
+        urllib.error.URLError: <urlopen error Invalid url: 'git://example.com/	' normalizes to 'git://example.com/'>
         """
         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
 
+        unparsed_url = urllib.parse.urlunparse(parsed_url)
+        if unparsed_url != url:
+            raise urllib.error.URLError("Invalid url: '%s' normalizes to '%s'" % (url, unparsed_url))
+
         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.
         """
         if self._empty:
             raise EmptyRepositoryError("There are no changesets yet")
 
         if revision in (None, '', 'tip', 'HEAD', 'head', -1):
             revision = -1
 
         if isinstance(revision, int):
             try:
                 return self.revisions[revision]
             except IndexError:
                 msg = "Revision %r does not exist for %s" % (revision, self.name)
                 raise ChangesetDoesNotExistError(msg)
 
         if isinstance(revision, str):
             if revision.isdigit() and (len(revision) < 12 or len(revision) == revision.count('0')):
                 try:
                     return self.revisions[int(revision)]
                 except IndexError:
                     msg = "Revision %r does not exist for %s" % (revision, self)
                     raise ChangesetDoesNotExistError(msg)
 
             # get by branch/tag name
             _ref_revision = self._parsed_refs.get(safe_bytes(revision))
             if _ref_revision:  # and _ref_revision[1] in [b'H', b'RH', b'T']:
                 return ascii_str(_ref_revision[0])
 
             if revision in self.revisions:
                 return revision
 
             # maybe it's a tag ? we don't have them in self.revisions
             if revision in self.tags.values():
                 return revision
 
             if SHA_PATTERN.match(revision):
                 msg = "Revision %r does not exist for %s" % (revision, self.name)
                 raise ChangesetDoesNotExistError(msg)
 
         raise ChangesetDoesNotExistError("Given revision %r not recognized" % revision)
 
     def get_ref_revision(self, ref_type, ref_name):
         """
         Returns ``GitChangeset`` object representing repository's
         changeset at the given ``revision``.
         """
         return self._get_revision(ref_name)
 
     def _get_archives(self, archive_name='tip'):
 
         for i in [('zip', '.zip'), ('gz', '.tar.gz'), ('bz2', '.tar.bz2')]:
             yield {"type": i[0], "extension": i[1], "node": archive_name}
 
     def _get_url(self, url):
         """
         Returns normalized url. If schema is not given, would fall to
         filesystem (``file:///``) schema.
         """
         if url != 'default' and '://' not in url:
             url = ':///'.join(('file', url))
         return url
 
     @LazyProperty
     def name(self):
         return os.path.basename(self.path)
 
     @LazyProperty
     def last_change(self):
         """
         Returns last change made on this repository as datetime object
         """
         return date_fromtimestamp(self._get_mtime(), makedate()[1])
 
     def _get_mtime(self):
         try:
             return time.mktime(self.get_changeset().date.timetuple())
         except RepositoryError:
             idx_loc = '' if self.bare else '.git'
             # fallback to filesystem
             in_path = os.path.join(self.path, idx_loc, "index")
             he_path = os.path.join(self.path, idx_loc, "HEAD")
             if os.path.exists(in_path):
                 return os.stat(in_path).st_mtime
             else:
                 return os.stat(he_path).st_mtime
 
     @LazyProperty
     def description(self):
         return safe_str(self._repo.get_description() or b'unknown')
 
     @property
     def branches(self):
         if not self.revisions:
             return {}
         _branches = [(safe_str(key), ascii_str(sha))
                      for key, (sha, type_) in self._parsed_refs.items() if type_ == b'H']
         return OrderedDict(sorted(_branches, key=(lambda ctx: ctx[0]), reverse=False))
 
     @LazyProperty
     def closed_branches(self):
         return {}
 
     @LazyProperty
     def tags(self):
         return self._get_tags()
 
     def _get_tags(self):
         if not self.revisions:
             return {}
         _tags = [(safe_str(key), ascii_str(sha))
                  for key, (sha, type_) in self._parsed_refs.items() if type_ == b'T']
         return OrderedDict(sorted(_tags, key=(lambda ctx: ctx[0]), reverse=True))
 
     def tag(self, name, user, revision=None, message=None, date=None,
             **kwargs):
         """
         Creates and returns a tag for the given ``revision``.
 
         :param name: name for new tag
         :param user: full username, i.e.: "Joe Doe <[e-mail]>"
         :param revision: changeset id for which new tag would be created
         :param message: message of the tag's commit
         :param date: date of tag's commit
 
         :raises TagAlreadyExistError: if tag with same name already exists
         """
         if name in self.tags:
             raise TagAlreadyExistError("Tag %s already exists" % name)
         changeset = self.get_changeset(revision)
         message = message or "Added tag %s for commit %s" % (name,
             changeset.raw_id)
         self._repo.refs[b"refs/tags/%s" % safe_bytes(name)] = changeset._commit.id
 
         self._parsed_refs = self._get_parsed_refs()
         self.tags = self._get_tags()
         return changeset
 
     def remove_tag(self, name, user, message=None, date=None):
         """
         Removes tag with the given ``name``.
 
         :param name: name of the tag to be removed
         :param user: full username, i.e.: "Joe Doe <[e-mail]>"
         :param message: message of the tag's removal commit
         :param date: date of tag's removal commit
 
         :raises TagDoesNotExistError: if tag with given name does not exists
         """
         if name not in self.tags:
             raise TagDoesNotExistError("Tag %s does not exist" % name)
         # self._repo.refs is a DiskRefsContainer, and .path gives the full absolute path of '.git'
         tagpath = os.path.join(safe_str(self._repo.refs.path), 'refs', 'tags', name)
         try:
             os.remove(tagpath)
             self._parsed_refs = self._get_parsed_refs()
             self.tags = self._get_tags()
         except OSError as e:
             raise RepositoryError(e.strerror)
 
     @LazyProperty
     def bookmarks(self):
         """
         Gets bookmarks for this repository
         """
         return {}
 
     @LazyProperty
     def _parsed_refs(self):
         return self._get_parsed_refs()
 
     def _get_parsed_refs(self):
         """Return refs as a dict, like:
         { b'v0.2.0': [b'599ba911aa24d2981225f3966eb659dfae9e9f30', b'T'] }
         """
         _repo = self._repo
         refs = _repo.get_refs()
         keys = [(b'refs/heads/', b'H'),
                 (b'refs/remotes/origin/', b'RH'),
                 (b'refs/tags/', b'T')]
         _refs = {}
         for ref, sha in refs.items():
             for k, type_ in keys:
                 if ref.startswith(k):
                     _key = ref[len(k):]
                     if type_ == b'T':
                         obj = _repo.get_object(sha)
                         if isinstance(obj, Tag):
                             sha = _repo.get_object(sha).object[1]
                     _refs[_key] = [sha, type_]
                     break
         return _refs
 
     def _heads(self, reverse=False):
         refs = self._repo.get_refs()
         heads = {}
 
         for key, val in refs.items():
             for ref_key in [b'refs/heads/', b'refs/remotes/origin/']:
                 if key.startswith(ref_key):
                     n = key[len(ref_key):]
                     if n not in [b'HEAD']:
                         heads[n] = val
 
         return heads if reverse else dict((y, x) for x, y in heads.items())
 
     def get_changeset(self, revision=None):
         """
         Returns ``GitChangeset`` object representing commit from git repository
         at the given revision or head (most recent commit) if None given.
         """
         if isinstance(revision, changeset.GitChangeset):
             return revision
         return changeset.GitChangeset(repository=self, revision=self._get_revision(revision))
 
     def get_changesets(self, start=None, end=None, start_date=None,
            end_date=None, branch_name=None, reverse=False, max_revisions=None):
         """
         Returns iterator of ``GitChangeset`` objects from start to end (both
         are inclusive), in ascending date order (unless ``reverse`` is set).
 
         :param start: changeset ID, as str; first returned changeset
         :param end: changeset ID, as str; last returned changeset
         :param start_date: if specified, changesets with commit date less than
           ``start_date`` would be filtered out from returned set
         :param end_date: if specified, changesets with commit date greater than
           ``end_date`` would be filtered out from returned set
         :param branch_name: if specified, changesets not reachable from given
           branch would be filtered out from returned set
         :param reverse: if ``True``, returned generator would be reversed
           (meaning that returned changesets would have descending date order)
 
         :raise BranchDoesNotExistError: If given ``branch_name`` does not
             exist.
         :raise ChangesetDoesNotExistError: If changeset for given ``start`` or
           ``end`` could not be found.
 
         """
         if branch_name and branch_name not in self.branches:
             raise BranchDoesNotExistError("Branch '%s' not found"
                                           % branch_name)
         # actually we should check now if it's not an empty repo to not spaw
         # subprocess commands
         if self._empty:
             raise EmptyRepositoryError("There are no changesets yet")
 
         # %H at format means (full) commit hash, initial hashes are retrieved
         # in ascending date order
         cmd = ['log', '--date-order', '--reverse', '--pretty=format:%H']
         if max_revisions:
             cmd += ['--max-count=%s' % max_revisions]
         if start_date:
             cmd += ['--since', start_date.strftime('%m/%d/%y %H:%M:%S')]
         if end_date:
             cmd += ['--until', end_date.strftime('%m/%d/%y %H:%M:%S')]
         if branch_name:
             cmd.append(branch_name)
         else:
             cmd.append(settings.GIT_REV_FILTER)
 
         revs = self.run_git_command(cmd).splitlines()
         start_pos = 0
         end_pos = len(revs)
         if start:
             _start = self._get_revision(start)
             try:
                 start_pos = revs.index(_start)
             except ValueError:
                 pass
 
         if end is not None:
             _end = self._get_revision(end)
             try:
                 end_pos = revs.index(_end)
             except ValueError:
                 pass
 
         if None not in [start, end] and start_pos > end_pos:
             raise RepositoryError('start cannot be after end')
 
         if end_pos is not None:
             end_pos += 1
 
         revs = revs[start_pos:end_pos]
         if reverse:
             revs.reverse()
 
         return CollectionGenerator(self, revs)
 
     def get_diff_changesets(self, org_rev, other_repo, other_rev):
         """
         Returns lists of changesets that can be merged from this repo @org_rev
         to other_repo @other_rev
         ... and the other way
         ... and the ancestors that would be used for merge
 
         :param org_rev: the revision we want our compare to be made
         :param other_repo: repo object, most likely the fork of org_repo. It has
             all changesets that we need to obtain
         :param other_rev: revision we want out compare to be made on other_repo
         """
         org_changesets = []
         ancestors = None
         if org_rev == other_rev:
             other_changesets = []
         elif self != other_repo:
             gitrepo = Repo(self.path)
             SubprocessGitClient(thin_packs=False).fetch(other_repo.path, gitrepo)
 
             gitrepo_remote = Repo(other_repo.path)
             SubprocessGitClient(thin_packs=False).fetch(self.path, gitrepo_remote)
 
             revs = [
                 ascii_str(x.commit.id)
                 for x in gitrepo_remote.get_walker(include=[ascii_bytes(other_rev)],
                                                    exclude=[ascii_bytes(org_rev)])
             ]
             other_changesets = [other_repo.get_changeset(rev) for rev in reversed(revs)]
             if other_changesets:
                 ancestors = [other_changesets[0].parents[0].raw_id]
             else:
                 # no changesets from other repo, ancestor is the other_rev
                 ancestors = [other_rev]
 
             gitrepo.close()
             gitrepo_remote.close()
 
         else:
             so = self.run_git_command(
                 ['log', '--reverse', '--pretty=format:%H',
                  '-s', '%s..%s' % (org_rev, other_rev)]
             )
             other_changesets = [self.get_changeset(cs)
                           for cs in re.findall(r'[0-9a-fA-F]{40}', so)]
             so = self.run_git_command(
                 ['merge-base', org_rev, other_rev]
             )
             ancestors = [re.findall(r'[0-9a-fA-F]{40}', so)[0]]
 
         return other_changesets, org_changesets, ancestors
 
     def get_diff(self, rev1, rev2, path=None, ignore_whitespace=False,
                  context=3):
         """
         Returns (git like) *diff*, as plain bytes text. Shows changes
         introduced by ``rev2`` since ``rev1``.
 
         :param rev1: Entry point from which diff is shown. Can be
           ``self.EMPTY_CHANGESET`` - in this case, patch showing all
           the changes since empty state of the repository until ``rev2``
         :param rev2: Until which revision changes should be shown.
         :param ignore_whitespace: If set to ``True``, would not show whitespace
           changes. Defaults to ``False``.
         :param context: How many lines before/after changed lines should be
           shown. Defaults to ``3``. Due to limitations in Git, if
           value passed-in is greater than ``2**31-1``
           (``2147483647``), it will be set to ``2147483647``
           instead. If negative value is passed-in, it will be set to
           ``0`` instead.
         """
 
         # Git internally uses a signed long int for storing context
         # size (number of lines to show before and after the
         # differences). This can result in integer overflow, so we
         # ensure the requested context is smaller by one than the
         # number that would cause the overflow. It is highly unlikely
         # that a single file will contain that many lines, so this
         # kind of change should not cause any realistic consequences.
         overflowed_long_int = 2**31
 
         if context >= overflowed_long_int:
             context = overflowed_long_int - 1
 
         # Negative context values make no sense, and will result in
         # errors. Ensure this does not happen.
         if context < 0:
             context = 0
 
         flags = ['-U%s' % context, '--full-index', '--binary', '-p', '-M', '--abbrev=40']
         if ignore_whitespace:
             flags.append('-w')
 
         if hasattr(rev1, 'raw_id'):
             rev1 = getattr(rev1, 'raw_id')
 
         if hasattr(rev2, 'raw_id'):
             rev2 = getattr(rev2, 'raw_id')
 
         if rev1 == self.EMPTY_CHANGESET:
             rev2 = self.get_changeset(rev2).raw_id
             cmd = ['show'] + flags + [rev2]
         else:
             rev1 = self.get_changeset(rev1).raw_id
             rev2 = self.get_changeset(rev2).raw_id
             cmd = ['diff'] + flags + [rev1, rev2]
 
         if path:
             cmd += ['--', path]
 
         stdout, stderr = self._run_git_command(cmd, cwd=self.path)
         # If we used 'show' command, strip first few lines (until actual diff
         # starts)
         if rev1 == self.EMPTY_CHANGESET:
             parts = stdout.split(b'\ndiff ', 1)
             if len(parts) > 1:
                 stdout = b'diff ' + parts[1]
         return stdout
 
     @LazyProperty
     def in_memory_changeset(self):
         """
         Returns ``GitInMemoryChangeset`` object for this repository.
         """
         return inmemory.GitInMemoryChangeset(self)
 
     def clone(self, url, update_after_clone=True, bare=False):
         """
         Tries to clone changes from external location.
 
         :param update_after_clone: If set to ``False``, git won't checkout
           working directory
         :param bare: If set to ``True``, repository would be cloned into
           *bare* git repository (no working directory at all).
         """
         url = self._get_url(url)
         cmd = ['clone', '-q']
         if bare:
             cmd.append('--bare')
         elif not update_after_clone:
             cmd.append('--no-checkout')
         cmd += ['--', url, self.path]
         # If error occurs run_git_command raises RepositoryError already
         self.run_git_command(cmd)
 
     def pull(self, url):
         """
         Tries to pull changes from external location.
         """
         url = self._get_url(url)
         cmd = ['pull', '--ff-only', url]
         # If error occurs run_git_command raises RepositoryError already
         self.run_git_command(cmd)
 
     def fetch(self, url):
         """
         Tries to pull changes from external location.
         """
         url = self._get_url(url)
         so = self.run_git_command(['ls-remote', '-h', url])
         cmd = ['fetch', url, '--']
         for line in so.splitlines():
             sha, ref = line.split('\t')
             cmd.append('+%s:%s' % (ref, ref))
         self.run_git_command(cmd)
 
     def _update_server_info(self):
         """
         runs gits update-server-info command in this repo instance
         """
         try:
             update_server_info(self._repo)
         except OSError as e:
             if e.errno not in [errno.ENOENT, errno.EROFS]:
                 raise
             # Workaround for dulwich crashing on for example its own dulwich/tests/data/repos/simple_merge.git/info/refs.lock
             log.error('Ignoring %s running update-server-info: %s', type(e).__name__, e)
 
     @LazyProperty
     def workdir(self):
         """
         Returns ``Workdir`` instance for this repository.
         """
         return workdir.GitWorkdir(self)
 
     def get_config_value(self, section, name, config_file=None):
         """
         Returns configuration value for a given [``section``] and ``name``.
 
         :param section: Section we want to retrieve value from
         :param name: Name of configuration we want to retrieve
         :param config_file: A path to file which should be used to retrieve
           configuration from (might also be a list of file paths)
         """
         if config_file is None:
             config_file = []
         elif isinstance(config_file, str):
             config_file = [config_file]
 
         def gen_configs():
             for path in config_file + self._config_files:
                 try:
                     yield ConfigFile.from_path(path)
                 except (IOError, OSError, ValueError):
                     continue
 
         for config in gen_configs():
             try:
                 value = config.get(section, name)
             except KeyError:
                 continue
             return None if value is None else safe_str(value)
         return None
 
     def get_user_name(self, config_file=None):
         """
         Returns user's name from global configuration file.
 
         :param config_file: A path to file which should be used to retrieve
           configuration from (might also be a list of file paths)
         """
         return self.get_config_value('user', 'name', config_file)
 
     def get_user_email(self, config_file=None):
         """
         Returns user's email from global configuration file.
 
         :param config_file: A path to file which should be used to retrieve
           configuration from (might also be a list of file paths)
         """
         return self.get_config_value('user', 'email', config_file)