view mercurial/statichttprepo.py @ 49000:dd6b67d5c256 stable

rust: fix unsound `OwningDirstateMap`

As per the previous patch, `OwningDirstateMap` is unsound. Self-referential
structs are difficult to implement correctly in Rust since the compiler is
free to move structs around as much as it wants to. They are also very rarely
needed in practice, so the state-of-the-art on how they should be done within
the Rust rules is still a bit new.

The crate `ouroboros` is an attempt at providing a safe way (in the Rust sense)
of declaring self-referential structs. It is getting a lot attention and was
improved very quickly when soundness issues were found in the past: rather than
relying on our own (limited) review circle, we might as well use the de-facto
common crate to fix this problem. This will give us a much better chance of
finding issues should any new ones be discovered as well as the benefit of
fewer `unsafe` APIs of our own.

I was starting to think about how I would present a safe API to the old struct
but soon realized that the callback-based approach was already done in
`ouroboros`, along with a lot more care towards refusing incorrect structs.

In short: we don't return a mutable reference to the `DirstateMap` anymore, we
expect users of its API to pass a `FnOnce` that takes the map as an argument.
This allows our `OwningDirstateMap` to control the input and output lifetimes
of the code that modifies it to prevent such issues.

Changing to `ouroboros` meant changing every API with it, but it is relatively
low churn in the end. It correctly identified the example buggy modification of
`copy_map_insert` outlined in the previous patch as violating the borrow rules.

Differential Revision: https://phab.mercurial-scm.org/D12429

# statichttprepo.py - simple http repository class for mercurial
#
# This provides read-only repo access to repositories exported via static http
#
# Copyright 2005-2007 Olivia Mackall <[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.

from __future__ import absolute_import

import errno

from .i18n import _
from .node import sha1nodeconstants
from . import (
    branchmap,
    changelog,
    error,
    localrepo,
    manifest,
    namespaces,
    pathutil,
    pycompat,
    requirements as requirementsmod,
    url,
    util,
    vfs as vfsmod,
)
from .utils import (
    urlutil,
)

urlerr = util.urlerr
urlreq = util.urlreq


class httprangereader(object):
    def __init__(self, url, opener):
        # we assume opener has HTTPRangeHandler
        self.url = url
        self.pos = 0
        self.opener = opener
        self.name = url

    def __enter__(self):
        return self

    def __exit__(self, exc_type, exc_value, traceback):
        self.close()

    def seek(self, pos):
        self.pos = pos

    def read(self, bytes=None):
        req = urlreq.request(pycompat.strurl(self.url))
        end = b''
        if bytes:
            end = self.pos + bytes - 1
        if self.pos or end:
            req.add_header('Range', 'bytes=%d-%s' % (self.pos, end))

        try:
            f = self.opener.open(req)
            data = f.read()
            code = f.code
        except urlerr.httperror as inst:
            num = inst.code == 404 and errno.ENOENT or None
            # Explicitly convert the exception to str as Py3 will try
            # convert it to local encoding and with as the HTTPResponse
            # instance doesn't support encode.
            raise IOError(num, str(inst))
        except urlerr.urlerror as inst:
            raise IOError(None, inst.reason)

        if code == 200:
            # HTTPRangeHandler does nothing if remote does not support
            # Range headers and returns the full entity. Let's slice it.
            if bytes:
                data = data[self.pos : self.pos + bytes]
            else:
                data = data[self.pos :]
        elif bytes:
            data = data[:bytes]
        self.pos += len(data)
        return data

    def readlines(self):
        return self.read().splitlines(True)

    def __iter__(self):
        return iter(self.readlines())

    def close(self):
        pass


# _RangeError and _HTTPRangeHandler were originally in byterange.py,
# which was itself extracted from urlgrabber. See the last version of
# byterange.py from history if you need more information.
class _RangeError(IOError):
    """Error raised when an unsatisfiable range is requested."""


class _HTTPRangeHandler(urlreq.basehandler):
    """Handler that enables HTTP Range headers.

    This was extremely simple. The Range header is a HTTP feature to
    begin with so all this class does is tell urllib2 that the
    "206 Partial Content" response from the HTTP server is what we
    expected.
    """

    def http_error_206(self, req, fp, code, msg, hdrs):
        # 206 Partial Content Response
        r = urlreq.addinfourl(fp, hdrs, req.get_full_url())
        r.code = code
        r.msg = msg
        return r

    def http_error_416(self, req, fp, code, msg, hdrs):
        # HTTP's Range Not Satisfiable error
        raise _RangeError(b'Requested Range Not Satisfiable')


def build_opener(ui, authinfo):
    # urllib cannot handle URLs with embedded user or passwd
    urlopener = url.opener(ui, authinfo)
    urlopener.add_handler(_HTTPRangeHandler())

    class statichttpvfs(vfsmod.abstractvfs):
        def __init__(self, base):
            self.base = base
            self.options = {}

        def __call__(self, path, mode=b'r', *args, **kw):
            if mode not in (b'r', b'rb'):
                raise IOError(b'Permission denied')
            f = b"/".join((self.base, urlreq.quote(path)))
            return httprangereader(f, urlopener)

        def join(self, path):
            if path:
                return pathutil.join(self.base, path)
            else:
                return self.base

    return statichttpvfs


class statichttppeer(localrepo.localpeer):
    def local(self):
        return None

    def canpush(self):
        return False


class statichttprepository(
    localrepo.localrepository, localrepo.revlogfilestorage
):
    supported = localrepo.localrepository._basesupported

    def __init__(self, ui, path):
        self._url = path
        self.ui = ui

        self.root = path
        u = urlutil.url(path.rstrip(b'/') + b"/.hg")
        self.path, authinfo = u.authinfo()

        vfsclass = build_opener(ui, authinfo)
        self.vfs = vfsclass(self.path)
        self.cachevfs = vfsclass(self.vfs.join(b'cache'))
        self._phasedefaults = []

        self.names = namespaces.namespaces()
        self.filtername = None
        self._extrafilterid = None
        self._wanted_sidedata = set()
        self.features = set()

        try:
            requirements = set(self.vfs.read(b'requires').splitlines())
        except IOError as inst:
            if inst.errno != errno.ENOENT:
                raise
            requirements = set()

            # check if it is a non-empty old-style repository
            try:
                fp = self.vfs(b"00changelog.i")
                fp.read(1)
                fp.close()
            except IOError as inst:
                if inst.errno != errno.ENOENT:
                    raise
                # we do not care about empty old-style repositories here
                msg = _(b"'%s' does not appear to be an hg repository") % path
                raise error.RepoError(msg)
        if requirementsmod.SHARESAFE_REQUIREMENT in requirements:
            storevfs = vfsclass(self.vfs.join(b'store'))
            requirements |= set(storevfs.read(b'requires').splitlines())

        supportedrequirements = localrepo.gathersupportedrequirements(ui)
        localrepo.ensurerequirementsrecognized(
            requirements, supportedrequirements
        )
        localrepo.ensurerequirementscompatible(ui, requirements)
        self.nodeconstants = sha1nodeconstants
        self.nullid = self.nodeconstants.nullid

        # setup store
        self.store = localrepo.makestore(requirements, self.path, vfsclass)
        self.spath = self.store.path
        self.svfs = self.store.opener
        self.sjoin = self.store.join
        self._filecache = {}
        self.requirements = requirements

        rootmanifest = manifest.manifestrevlog(self.nodeconstants, self.svfs)
        self.manifestlog = manifest.manifestlog(
            self.svfs, self, rootmanifest, self.narrowmatch()
        )
        self.changelog = changelog.changelog(self.svfs)
        self._tags = None
        self.nodetagscache = None
        self._branchcaches = branchmap.BranchMapCache()
        self._revbranchcache = None
        self.encodepats = None
        self.decodepats = None
        self._transref = None

    def _restrictcapabilities(self, caps):
        caps = super(statichttprepository, self)._restrictcapabilities(caps)
        return caps.difference([b"pushkey"])

    def url(self):
        return self._url

    def local(self):
        return False

    def peer(self):
        return statichttppeer(self)

    def wlock(self, wait=True):
        raise error.LockUnavailable(
            0,
            _(b'lock not available'),
            b'lock',
            _(b'cannot lock static-http repository'),
        )

    def lock(self, wait=True):
        raise error.LockUnavailable(
            0,
            _(b'lock not available'),
            b'lock',
            _(b'cannot lock static-http repository'),
        )

    def _writecaches(self):
        pass  # statichttprepository are read only


def instance(ui, path, create, intents=None, createopts=None):
    if create:
        raise error.Abort(_(b'cannot create new static-http repository'))
    return statichttprepository(ui, path[7:])