annotate hgext/acl.py @ 27220:4374d819ccd5

mercurial: implement import hook for handling C/Python modules

There are a handful of modules that have both pure Python and C
extension implementations. Currently, setup.py copies files from
mercurial/pure/*.py to mercurial/ during the install process if C
extensions are not available. This way, "import mercurial.X" will
work whether C extensions are available or not.

This approach has a few drawbacks. First, there aren't run-time checks
verifying the C extensions are loaded when they should be. This could
lead to accidental use of the slower pure Python modules. Second, the
C extensions aren't compatible with PyPy and running Mercurial with
PyPy requires installing Mercurial - you can't run ./hg from a source
checkout. This makes developing while running PyPy somewhat difficult.

This patch implements a PEP-302 import hook for finding and loading the
modules with both C and Python implementations. When a module with dual
implementations is requested for import, its import is handled by our
import hook.

The importer has a mechanism that controls what types of modules we
allow to load. We call this loading behavior the "module load policy."
There are 3 settings:

* Only load C extensions
* Only load pure Python
* Try to load C and fall back to Python

An environment variable allows overriding this policy at run time. This
is mainly useful for developers and for performing actions against the
source checkout (such as installing), which require overriding the
default (strict) policy about requiring C extensions.

The default mode for now is to allow both. This isn't proper and is
technically backwards incompatible. However, it is necessary to
implement a sane patch series that doesn't break the world during
future bisections. The behavior will be corrected in future patch.

We choose the main mercurial/__init__.py module for this code out of
necessity: in a future world, if the custom module importer isn't
registered, we'll fail to find/import certain modules when running
from a pure installation. Without the magical import-time side-effects,
*any* importer of mercurial.* modules would be required to call a
function to register our importer. I'm not a fan of import time side
effects and I initially attempted to do this. However, I was foiled by
our own test harness, which has numerous `python` invoked scripts that
"import mercurial" and fail because the importer isn't registered.
Realizing this problem is probably present in random Python scripts
that have been written over the years, I decided that sacrificing
purity for backwards compatibility is necessary. Plus, if you are
programming Python, "import" should probably "just work."

It's worth noting that now that we have a custom module loader, it
would be possible to hook up demand module proxies at this level
instead of replacing __import__. We leave this work for another time,
if it's even desired.

This patch breaks importing in environments where Mercurial modules
are loaded from a zip file (such as py2exe distributions). This will
be addressed in a subsequent patch.

# acl.py - changeset access control for mercurial
#
# Copyright 2006 Vadim Gelfer <[e-mail]>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

'''hooks for controlling repository access

This hook makes it possible to allow or deny write access to given
branches and paths of a repository when receiving incoming changesets
via pretxnchangegroup and pretxncommit.

The authorization is matched based on the local user name on the
system where the hook runs, and not the committer of the original
changeset (since the latter is merely informative).

The acl hook is best used along with a restricted shell like hgsh,
preventing authenticating users from doing anything other than pushing
or pulling. The hook is not safe to use if users have interactive
shell access, as they can then disable the hook. Nor is it safe if
remote users share an account, because then there is no way to
distinguish them.

The order in which access checks are performed is:

1) Deny  list for branches (section ``acl.deny.branches``)
2) Allow list for branches (section ``acl.allow.branches``)
3) Deny  list for paths    (section ``acl.deny``)
4) Allow list for paths    (section ``acl.allow``)

The allow and deny sections take key-value pairs.

Branch-based Access Control
---------------------------

Use the ``acl.deny.branches`` and ``acl.allow.branches`` sections to
have branch-based access control. Keys in these sections can be
either:

- a branch name, or
- an asterisk, to match any branch;

The corresponding values can be either:

- a comma-separated list containing users and groups, or
- an asterisk, to match anyone;

You can add the "!" prefix to a user or group name to invert the sense
of the match.

Path-based Access Control
-------------------------

Use the ``acl.deny`` and ``acl.allow`` sections to have path-based
access control. Keys in these sections accept a subtree pattern (with
a glob syntax by default). The corresponding values follow the same
syntax as the other sections above.

Groups
------

Group names must be prefixed with an ``@`` symbol. Specifying a group
name has the same effect as specifying all the users in that group.

You can define group members in the ``acl.groups`` section.
If a group name is not defined there, and Mercurial is running under
a Unix-like system, the list of users will be taken from the OS.
Otherwise, an exception will be raised.

Example Configuration
---------------------

::

  [hooks]

  # Use this if you want to check access restrictions at commit time
  pretxncommit.acl = python:hgext.acl.hook

  # Use this if you want to check access restrictions for pull, push,
  # bundle and serve.
  pretxnchangegroup.acl = python:hgext.acl.hook

  [acl]
  # Allow or deny access for incoming changes only if their source is
  # listed here, let them pass otherwise. Source is "serve" for all
  # remote access (http or ssh), "push", "pull" or "bundle" when the
  # related commands are run locally.
  # Default: serve
  sources = serve

  [acl.deny.branches]

  # Everyone is denied to the frozen branch:
  frozen-branch = *

  # A bad user is denied on all branches:
  * = bad-user

  [acl.allow.branches]

  # A few users are allowed on branch-a:
  branch-a = user-1, user-2, user-3

  # Only one user is allowed on branch-b:
  branch-b = user-1

  # The super user is allowed on any branch:
  * = super-user

  # Everyone is allowed on branch-for-tests:
  branch-for-tests = *

  [acl.deny]
  # This list is checked first. If a match is found, acl.allow is not
  # checked. All users are granted access if acl.deny is not present.
  # Format for both lists: glob pattern = user, ..., @group, ...

  # To match everyone, use an asterisk for the user:
  # my/glob/pattern = *

  # user6 will not have write access to any file:
  ** = user6

  # Group "hg-denied" will not have write access to any file:
  ** = @hg-denied

  # Nobody will be able to change "DONT-TOUCH-THIS.txt", despite
  # everyone being able to change all other files. See below.
  src/main/resources/DONT-TOUCH-THIS.txt = *

  [acl.allow]
  # if acl.allow is not present, all users are allowed by default
  # empty acl.allow = no users allowed

  # User "doc_writer" has write access to any file under the "docs"
  # folder:
  docs/** = doc_writer

  # User "jack" and group "designers" have write access to any file
  # under the "images" folder:
  images/** = jack, @designers

  # Everyone (except for "user6" and "@hg-denied" - see acl.deny above)
  # will have write access to any file under the "resources" folder
  # (except for 1 file. See acl.deny):
  src/main/resources/** = *

  .hgtags = release_engineer

Examples using the "!" prefix
.............................

Suppose there's a branch that only a given user (or group) should be able to
push to, and you don't want to restrict access to any other branch that may
be created.

The "!" prefix allows you to prevent anyone except a given user or group to
push changesets in a given branch or path.

In the examples below, we will:
1) Deny access to branch "ring" to anyone but user "gollum"
2) Deny access to branch "lake" to anyone but members of the group "hobbit"
3) Deny access to a file to anyone but user "gollum"

::

  [acl.allow.branches]
  # Empty

  [acl.deny.branches]

  # 1) only 'gollum' can commit to branch 'ring';
  # 'gollum' and anyone else can still commit to any other branch.
  ring = !gollum

  # 2) only members of the group 'hobbit' can commit to branch 'lake';
  # 'hobbit' members and anyone else can still commit to any other branch.
  lake = !@hobbit

  # You can also deny access based on file paths:

  [acl.allow]
  # Empty

  [acl.deny]
  # 3) only 'gollum' can change the file below;
  # 'gollum' and anyone else can still change any other file.
  /misty/mountains/cave/ring = !gollum

'''

from mercurial.i18n import _
from mercurial import util, match, error
import getpass, urllib

# Note for extension authors: ONLY specify testedwith = 'internal' for
# extensions which SHIP WITH MERCURIAL. Non-mainline extensions should
# be specifying the version(s) of Mercurial they are tested with, or
# leave the attribute unspecified.
testedwith = 'internal'

def _getusers(ui, group):

    # First, try to use group definition from section [acl.groups]
    hgrcusers = ui.configlist('acl.groups', group)
    if hgrcusers:
        return hgrcusers

    ui.debug('acl: "%s" not defined in [acl.groups]\n' % group)
    # If no users found in group definition, get users from OS-level group
    try:
        return util.groupmembers(group)
    except KeyError:
        raise error.Abort(_("group '%s' is undefined") % group)

def _usermatch(ui, user, usersorgroups):

    if usersorgroups == '*':
        return True

    for ug in usersorgroups.replace(',', ' ').split():

        if ug.startswith('!'):
            # Test for excluded user or group. Format:
            # if ug is a user  name: !username
            # if ug is a group name: !@groupname
            ug = ug[1:]
            if not ug.startswith('@') and user != ug \
                or ug.startswith('@') and user not in _getusers(ui, ug[1:]):
                return True

        # Test for user or group. Format:
        # if ug is a user  name: username
        # if ug is a group name: @groupname
        elif user == ug \
             or ug.startswith('@') and user in _getusers(ui, ug[1:]):
            return True

    return False

def buildmatch(ui, repo, user, key):
    '''return tuple of (match function, list enabled).'''
    if not ui.has_section(key):
        ui.debug('acl: %s not enabled\n' % key)
        return None

    pats = [pat for pat, users in ui.configitems(key)
            if _usermatch(ui, user, users)]
    ui.debug('acl: %s enabled, %d entries for user %s\n' %
             (key, len(pats), user))

    # Branch-based ACL
    if not repo:
        if pats:
            # If there's an asterisk (meaning "any branch"), always return True;
            # Otherwise, test if b is in pats
            if '*' in pats:
                return util.always
            return lambda b: b in pats
        return util.never

    # Path-based ACL
    if pats:
        return match.match(repo.root, '', pats)
    return util.never

def hook(ui, repo, hooktype, node=None, source=None, **kwargs):
    if hooktype not in ['pretxnchangegroup', 'pretxncommit']:
        raise error.Abort(_('config error - hook type "%s" cannot stop '
                           'incoming changesets nor commits') % hooktype)
    if (hooktype == 'pretxnchangegroup' and
        source not in ui.config('acl', 'sources', 'serve').split()):
        ui.debug('acl: changes have source "%s" - skipping\n' % source)
        return

    user = None
    if source == 'serve' and 'url' in kwargs:
        url = kwargs['url'].split(':')
        if url[0] == 'remote' and url[1].startswith('http'):
            user = urllib.unquote(url[3])

    if user is None:
        user = getpass.getuser()

    ui.debug('acl: checking access for user "%s"\n' % user)

    # deprecated config: acl.config
    cfg = ui.config('acl', 'config')
    if cfg:
        ui.readconfig(cfg, sections=['acl.groups', 'acl.allow.branches',
            'acl.deny.branches', 'acl.allow', 'acl.deny'])

    allowbranches = buildmatch(ui, None, user, 'acl.allow.branches')
    denybranches = buildmatch(ui, None, user, 'acl.deny.branches')
    allow = buildmatch(ui, repo, user, 'acl.allow')
    deny = buildmatch(ui, repo, user, 'acl.deny')

    for rev in xrange(repo[node], len(repo)):
        ctx = repo[rev]
        branch = ctx.branch()
        if denybranches and denybranches(branch):
            raise error.Abort(_('acl: user "%s" denied on branch "%s"'
                               ' (changeset "%s")')
                               % (user, branch, ctx))
        if allowbranches and not allowbranches(branch):
            raise error.Abort(_('acl: user "%s" not allowed on branch "%s"'
                               ' (changeset "%s")')
                               % (user, branch, ctx))
        ui.debug('acl: branch access granted: "%s" on branch "%s"\n'
        % (ctx, branch))

        for f in ctx.files():
            if deny and deny(f):
                raise error.Abort(_('acl: user "%s" denied on "%s"'
                ' (changeset "%s")') % (user, f, ctx))
            if allow and not allow(f):
                raise error.Abort(_('acl: user "%s" not allowed on "%s"'
                ' (changeset "%s")') % (user, f, ctx))
        ui.debug('acl: path access granted: "%s"\n' % ctx)