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# Copyright (C) 2011 Canonical Ltd
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
"""Branch opening with URL-based restrictions."""
from __future__ import absolute_import
import threading
from bzrlib import (
errors,
urlutils,
)
from bzrlib.branch import Branch
from bzrlib.controldir import (
ControlDir,
)
class BadUrl(errors.BzrError):
_fmt = "Tried to access a branch from bad URL %(url)s."
class BranchReferenceForbidden(errors.BzrError):
_fmt = ("Trying to mirror a branch reference and the branch type "
"does not allow references.")
class BranchLoopError(errors.BzrError):
"""Encountered a branch cycle.
A URL may point to a branch reference or it may point to a stacked branch.
In either case, it's possible for there to be a cycle in these references,
and this exception is raised when we detect such a cycle.
"""
_fmt = "Encountered a branch cycle"""
class BranchOpenPolicy(object):
"""Policy on how to open branches.
In particular, a policy determines which branches are okay to open by
checking their URLs and deciding whether or not to follow branch
references.
"""
def should_follow_references(self):
"""Whether we traverse references when mirroring.
Subclasses must override this method.
If we encounter a branch reference and this returns false, an error is
raised.
:returns: A boolean to indicate whether to follow a branch reference.
"""
raise NotImplementedError(self.should_follow_references)
def transform_fallback_location(self, branch, url):
"""Validate, maybe modify, 'url' to be used as a stacked-on location.
:param branch: The branch that is being opened.
:param url: The URL that the branch provides for its stacked-on
location.
:return: (new_url, check) where 'new_url' is the URL of the branch to
actually open and 'check' is true if 'new_url' needs to be
validated by check_and_follow_branch_reference.
"""
raise NotImplementedError(self.transform_fallback_location)
def check_one_url(self, url):
"""Check a URL.
Subclasses must override this method.
:param url: The source URL to check.
:raise BadUrl: subclasses are expected to raise this or a subclass
when it finds a URL it deems to be unacceptable.
"""
raise NotImplementedError(self.check_one_url)
class _BlacklistPolicy(BranchOpenPolicy):
"""Branch policy that forbids certain URLs.
This doesn't cope with various alternative spellings of URLs,
with e.g. url encoding. It's mostly useful for tests.
"""
def __init__(self, should_follow_references, bad_urls=None):
if bad_urls is None:
bad_urls = set()
self._bad_urls = bad_urls
self._should_follow_references = should_follow_references
def should_follow_references(self):
return self._should_follow_references
def check_one_url(self, url):
if url in self._bad_urls:
raise BadUrl(url)
def transform_fallback_location(self, branch, url):
"""See `BranchOpenPolicy.transform_fallback_location`.
This class is not used for testing our smarter stacking features so we
just do the simplest thing: return the URL that would be used anyway
and don't check it.
"""
return urlutils.join(branch.base, url), False
class AcceptAnythingPolicy(_BlacklistPolicy):
"""Accept anything, to make testing easier."""
def __init__(self):
super(AcceptAnythingPolicy, self).__init__(True, set())
class WhitelistPolicy(BranchOpenPolicy):
"""Branch policy that only allows certain URLs."""
def __init__(self, should_follow_references, allowed_urls=None,
check=False):
if allowed_urls is None:
allowed_urls = []
self.allowed_urls = set(url.rstrip('/') for url in allowed_urls)
self.check = check
def should_follow_references(self):
return self._should_follow_references
def check_one_url(self, url):
if url.rstrip('/') not in self.allowed_urls:
raise BadUrl(url)
def transform_fallback_location(self, branch, url):
"""See `BranchOpenPolicy.transform_fallback_location`.
Here we return the URL that would be used anyway and optionally check
it.
"""
return urlutils.join(branch.base, url), self.check
class SingleSchemePolicy(BranchOpenPolicy):
"""Branch open policy that rejects URLs not on the given scheme."""
def __init__(self, allowed_scheme):
self.allowed_scheme = allowed_scheme
def should_follow_references(self):
return True
def transform_fallback_location(self, branch, url):
return urlutils.join(branch.base, url), True
def check_one_url(self, url):
"""Check that `url` is okay to open."""
if urlutils.URL.from_string(str(url)).scheme != self.allowed_scheme:
raise BadUrl(url)
class BranchOpener(object):
"""Branch opener which uses a URL policy.
All locations that are opened (stacked-on branches, references) are
checked against a policy object.
The policy object is expected to have the following methods:
* check_one_url
* should_follow_references
* transform_fallback_location
"""
_threading_data = threading.local()
def __init__(self, policy, probers=None):
"""Create a new BranchOpener.
:param policy: The opener policy to use.
:param probers: Optional list of probers to allow.
Defaults to local and remote bzr probers.
"""
self.policy = policy
self._seen_urls = set()
self.probers = probers
@classmethod
def install_hook(cls):
"""Install the ``transform_fallback_location`` hook.
This is done at module import time, but transform_fallback_locationHook
doesn't do anything unless the `_active_openers` threading.Local
object has a 'opener' attribute in this thread.
This is in a module-level function rather than performed at module
level so that it can be called in setUp for testing `BranchOpener`
as bzrlib.tests.TestCase.setUp clears hooks.
"""
Branch.hooks.install_named_hook(
'transform_fallback_location',
cls.transform_fallback_locationHook,
'BranchOpener.transform_fallback_locationHook')
def check_and_follow_branch_reference(self, url):
"""Check URL (and possibly the referenced URL).
This method checks that `url` passes the policy's `check_one_url`
method, and if `url` refers to a branch reference, it checks whether
references are allowed and whether the reference's URL passes muster
also -- recursively, until a real branch is found.
:param url: URL to check
:raise BranchLoopError: If the branch references form a loop.
:raise BranchReferenceForbidden: If this opener forbids branch
references.
"""
while True:
if url in self._seen_urls:
raise BranchLoopError()
self._seen_urls.add(url)
self.policy.check_one_url(url)
next_url = self.follow_reference(url)
if next_url is None:
return url
url = next_url
if not self.policy.should_follow_references():
raise BranchReferenceForbidden(url)
@classmethod
def transform_fallback_locationHook(cls, branch, url):
"""Installed as the 'transform_fallback_location' Branch hook.
This method calls `transform_fallback_location` on the policy object and
either returns the url it provides or passes it back to
check_and_follow_branch_reference.
"""
try:
opener = getattr(cls._threading_data, "opener")
except AttributeError:
return url
new_url, check = opener.policy.transform_fallback_location(branch, url)
if check:
return opener.check_and_follow_branch_reference(new_url)
else:
return new_url
def run_with_transform_fallback_location_hook_installed(
self, callable, *args, **kw):
if (self.transform_fallback_locationHook not in
Branch.hooks['transform_fallback_location']):
raise AssertionError("hook not installed")
self._threading_data.opener = self
try:
return callable(*args, **kw)
finally:
del self._threading_data.opener
# We reset _seen_urls here to avoid multiple calls to open giving
# spurious loop exceptions.
self._seen_urls = set()
def follow_reference(self, url):
"""Get the branch-reference value at the specified url.
This exists as a separate method only to be overriden in unit tests.
"""
bzrdir = ControlDir.open(url, probers=self.probers)
return bzrdir.get_branch_reference()
def open(self, url):
"""Open the Bazaar branch at url, first checking it.
What is acceptable means is defined by the policy's `follow_reference` and
`check_one_url` methods.
"""
if type(url) != str:
raise TypeError
url = self.check_and_follow_branch_reference(url)
def open_branch(url):
dir = ControlDir.open(url, probers=self.probers)
return dir.open_branch()
return self.run_with_transform_fallback_location_hook_installed(
open_branch, url)
def open_only_scheme(allowed_scheme, url):
"""Open the branch at `url`, only accessing URLs on `allowed_scheme`.
:raises BadUrl: An attempt was made to open a URL that was not on
`allowed_scheme`.
"""
return BranchOpener(SingleSchemePolicy(allowed_scheme)).open(url)
BranchOpener.install_hook()
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