/brz/remove-bazaar

# 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

"""Safe branch opening."""

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 safe 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 the safety of the source 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 unsafe.

        """

        raise NotImplementedError(self.check_one_url)

class BlacklistPolicy(BranchOpenPolicy):

    """Branch policy that forbids certain URLs."""

    def __init__(self, should_follow_references, unsafe_urls=None):

        if unsafe_urls is None:

            unsafe_urls = set()

        self._unsafe_urls = unsafe_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._unsafe_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 safe to open."""

        if urlutils.URL.from_string(str(url)).scheme != self.allowed_scheme:

            raise BadUrl(url)

class SafeBranchOpener(object):

    """Safe branch opener.

    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 SafeBranchOpener.

        :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 `SafeBranchOpener`

        as bzrlib.tests.TestCase.setUp clears hooks.

        """

        Branch.hooks.install_named_hook(

            'transform_fallback_location',

            cls.transform_fallback_locationHook,

            'SafeBranchOpener.transform_fallback_locationHook')

    def check_and_follow_branch_reference(self, url):

        """Check URL (and possibly the referenced URL) for safety.

        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):

        assert (self.transform_fallback_locationHook in

                Branch.hooks['transform_fallback_location'])

        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 for safety.

        What safety means is defined by a subclasses `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 safe_open(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 SafeBranchOpener(SingleSchemePolicy(allowed_scheme)).open(url)

SafeBranchOpener.install_hook()