When updating from a mirror, just ignore out-of-date copies.

[zeroinstall/zeroinstall-mseaborn.git] / zeroinstall / injector / iface_cache.py

"""
Manages the feed cache.

@var iface_cache: A singleton cache object. You should normally use this rather than
creating new cache objects.
"""
# Copyright (C) 2008, Thomas Leonard
# See the README file for details, or visit http://0install.net.

# Note:
#
# We need to know the modification time of each interface, because we refuse
# to update to an older version (this prevents an attack where the attacker
# sends back an old version which is correctly signed but has a known bug).
#
# The way we store this is a bit complicated due to backward compatibility:
#
# - GPG-signed interfaces have their signatures removed and a last-modified
#   attribute is stored containing the date from the signature.
#
# - XML-signed interfaces are stored unmodified with their signatures. The
#   date is extracted from the signature when needed.
#
# - Older versions used to add the last-modified attribute even to files
#   with XML signatures - these files therefore have invalid signatures and
#   we extract from the attribute for these.
#
# Eventually, support for the first and third cases will be removed.

import os, sys, time
from logging import debug, info, warn
from cStringIO import StringIO

from zeroinstall.support import basedir
from zeroinstall.injector import reader, model
from zeroinstall.injector.namespaces import *
from zeroinstall.injector.model import *
from zeroinstall import zerostore

def _pretty_time(t):
        assert isinstance(t, (int, long)), t
        return time.strftime('%Y-%m-%d %H:%M:%S UTC', time.localtime(t))

class ReplayAttack(SafeException):
        """Attempt to import a feed that's older than the one in the cache."""
        pass

class PendingFeed(object):
        """A feed that has been downloaded but not yet added to the interface cache.
        Feeds remain in this state until the user confirms that they trust at least
        one of the signatures.
        @ivar url: URL for the feed
        @type url: str
        @ivar signed_data: the untrusted data
        @type signed_data: stream
        @ivar sigs: signatures extracted from signed_data
        @type sigs: [L{gpg.Signature}]
        @ivar new_xml: the payload of the signed_data, or the whole thing if XML
        @type new_xml: str
        @since: 0.25"""
        __slots__ = ['url', 'signed_data', 'sigs', 'new_xml']

        def __init__(self, url, signed_data):
                """Downloaded data is a GPG-signed message.
                @param url: the URL of the downloaded feed
                @type url: str
                @param signed_data: the downloaded data (not yet trusted)
                @type signed_data: stream
                @raise SafeException: if the data is not signed, and logs the actual data"""
                self.url = url
                self.signed_data = signed_data
                self.recheck()

        def download_keys(self, handler, feed_hint = None, key_mirror = None):
                """Download any required GPG keys not already on our keyring.
                When all downloads are done (successful or otherwise), add any new keys
                to the keyring, L{recheck}.
                @param handler: handler to manage the download
                @type handler: L{handler.Handler}
                @param key_mirror: URL of directory containing keys, or None to use feed's directory
                @type key_mirror: str
                """
                downloads = {}
                blockers = []
                for x in self.sigs:
                        key_id = x.need_key()
                        if key_id:
                                import urlparse
                                key_url = urlparse.urljoin(key_mirror or self.url, '%s.gpg' % key_id)
                                info("Fetching key from %s", key_url)
                                dl = handler.get_download(key_url, hint = feed_hint)
                                downloads[dl.downloaded] = (dl, dl.tempfile)
                                blockers.append(dl.downloaded)

                exception = None
                any_success = False

                from zeroinstall.support import tasks

                while blockers:
                        yield blockers

                        old_blockers = blockers
                        blockers = []

                        for b in old_blockers:
                                try:
                                        tasks.check(b)
                                        if b.happened:
                                                dl, stream = downloads[b]
                                                stream.seek(0)
                                                self._downloaded_key(stream)
                                                any_success = True
                                        else:
                                                blockers.append(b)
                                except Exception:
                                        _, exception, tb = sys.exc_info()
                                        warn("Failed to import key for '%s': %s", self.url, str(exception))

                if exception and not any_success:
                        raise exception, None, tb

                self.recheck()

        def _downloaded_key(self, stream):
                import shutil, tempfile
                from zeroinstall.injector import gpg

                info("Importing key for feed '%s'", self.url)

                # Python2.4: can't call fileno() on stream, so save to tmp file instead
                tmpfile = tempfile.TemporaryFile(prefix = 'injector-dl-data-')
                try:
                        shutil.copyfileobj(stream, tmpfile)
                        tmpfile.flush()

                        tmpfile.seek(0)
                        gpg.import_key(tmpfile)
                finally:
                        tmpfile.close()

        def recheck(self):
                """Set new_xml and sigs by reading signed_data.
                You need to call this when previously-missing keys are added to the GPG keyring."""
                import gpg
                try:
                        self.signed_data.seek(0)
                        stream, sigs = gpg.check_stream(self.signed_data)
                        assert sigs

                        data = stream.read()
                        if stream is not self.signed_data:
                                stream.close()

                        self.new_xml = data
                        self.sigs = sigs
                except:
                        self.signed_data.seek(0)
                        info("Failed to check GPG signature. Data received was:\n" + `self.signed_data.read()`)
                        raise

class IfaceCache(object):
        """
        The interface cache stores downloaded and verified interfaces in
        ~/.cache/0install.net/interfaces (by default).

        There are methods to query the cache, add to it, check signatures, etc.

        The cache is updated by L{fetch.Fetcher}.

        Confusingly, this class is really two caches combined: the in-memory
        cache of L{model.Interface} objects, and an on-disk cache of L{model.ZeroInstallFeed}s.
        It will probably be split into two in future.

        @ivar pending: downloaded feeds which are not yet trusted
        @type pending: str -> PendingFeed
        @see: L{iface_cache} - the singleton IfaceCache instance.
        """

        __slots__ = ['_interfaces', 'stores', 'pending']

        def __init__(self):
                self._interfaces = {}
                self.pending = {}

                self.stores = zerostore.Stores()
        
        def add_pending(self, pending):
                """Add a PendingFeed to the pending dict.
                @param pending: the untrusted download to add
                @type pending: PendingFeed
                @since: 0.25"""
                assert isinstance(pending, PendingFeed)
                self.pending[pending.url] = pending
        
        def update_interface_if_trusted(self, interface, sigs, xml):
                """Update a cached interface (using L{update_interface_from_network})
                if we trust the signatures, and remove it from L{pending}.
                If we don't trust any of the signatures, do nothing.
                @param interface: the interface being updated
                @type interface: L{model.Interface}
                @param sigs: signatures from L{gpg.check_stream}
                @type sigs: [L{gpg.Signature}]
                @param xml: the downloaded replacement interface document
                @type xml: str
                @return: True if the interface was updated
                @rtype: bool
                @precondition: call L{add_pending}
                """
                import trust
                updated = self._oldest_trusted(sigs, trust.domain_from_url(interface.uri))
                if updated is None: return False        # None are trusted
        
                if interface.uri in self.pending:
                        del self.pending[interface.uri]
                else:
                        raise Exception("update_interface_if_trusted, but '%s' not pending!" % interface.uri)

                self.update_interface_from_network(interface, xml, updated)
                return True

        def update_interface_from_network(self, interface, new_xml, modified_time):
                """Update a cached interface.
                Called by L{update_interface_if_trusted} if we trust this data.
                After a successful update, L{writer} is used to update the interface's
                last_checked time.
                @param interface: the interface being updated
                @type interface: L{model.Interface}
                @param new_xml: the downloaded replacement interface document
                @type new_xml: str
                @param modified_time: the timestamp of the oldest trusted signature
                (used as an approximation to the interface's modification time)
                @type modified_time: long
                @raises SafeException: if modified_time is older than the currently cached time
                """
                debug("Updating '%s' from network; modified at %s" %
                        (interface.name or interface.uri, _pretty_time(modified_time)))

                if '\n<!-- Base64 Signature' not in new_xml:
                        # Only do this for old-style interfaces without
                        # signatures Otherwise, we can get the time from the
                        # signature, and adding this attribute just makes the
                        # signature invalid.
                        from xml.dom import minidom
                        doc = minidom.parseString(new_xml)
                        doc.documentElement.setAttribute('last-modified', str(modified_time))
                        new_xml = StringIO()
                        doc.writexml(new_xml)
                        new_xml = new_xml.getvalue()

                self._import_new_interface(interface, new_xml, modified_time)

                import writer
                interface._main_feed.last_checked = long(time.time())
                writer.save_interface(interface)

                info("Updated interface cache entry for %s (modified %s)",
                        interface.get_name(), _pretty_time(modified_time))

        def _import_new_interface(self, interface, new_xml, modified_time):
                """Write new_xml into the cache.
                @param interface: updated once the new XML is written
                @param new_xml: the data to write
                @param modified_time: when new_xml was modified
                @raises SafeException: if the new mtime is older than the current one
                """
                assert modified_time

                upstream_dir = basedir.save_cache_path(config_site, 'interfaces')
                cached = os.path.join(upstream_dir, escape(interface.uri))

                if os.path.exists(cached):
                        old_xml = file(cached).read()
                        if old_xml == new_xml:
                                debug("No change")
                                return

                stream = file(cached + '.new', 'w')
                stream.write(new_xml)
                stream.close()
                os.utime(cached + '.new', (modified_time, modified_time))
                new_mtime = reader.check_readable(interface.uri, cached + '.new')
                assert new_mtime == modified_time

                old_modified = self._get_signature_date(interface.uri)
                if old_modified is None:
                        old_modified = interface.last_modified

                if old_modified:
                        if new_mtime < old_modified:
                                os.unlink(cached + '.new')
                                raise ReplayAttack("New interface's modification time is before old "
                                                    "version!"
                                                    "\nOld time: " + _pretty_time(old_modified) +
                                                    "\nNew time: " + _pretty_time(new_mtime) + 
                                                    "\nRefusing update.")
                        if new_mtime == old_modified:
                                # You used to have to update the modification time manually.
                                # Now it comes from the signature, this check isn't useful
                                # and often causes problems when the stored format changes
                                # (e.g., when we stopped writing last-modified attributes)
                                pass
                                #raise SafeException("Interface has changed, but modification time "
                                #                   "hasn't! Refusing update.")
                os.rename(cached + '.new', cached)
                debug("Saved as " + cached)

                reader.update_from_cache(interface)

        def get_feed(self, url):
                """Get a feed from the cache.
                @param url: the URL of the feed
                @return: the feed, or None if it isn't cached
                @rtype: L{model.ZeroInstallFeed}"""
                # TODO: This isn't a good implementation
                iface = self.get_interface(url)
                feed = iface._main_feed
                if not isinstance(feed, model.DummyFeed):
                        return feed
                return None

        def get_interface(self, uri):
                """Get the interface for uri, creating a new one if required.
                New interfaces are initialised from the disk cache, but not from
                the network.
                @param uri: the URI of the interface to find
                @rtype: L{model.Interface}
                """
                if type(uri) == str:
                        uri = unicode(uri)
                assert isinstance(uri, unicode)

                if uri in self._interfaces:
                        return self._interfaces[uri]

                debug("Initialising new interface object for %s", uri)
                self._interfaces[uri] = Interface(uri)
                reader.update_from_cache(self._interfaces[uri])
                return self._interfaces[uri]

        def list_all_interfaces(self):
                """List all interfaces in the cache.
                @rtype: [str]
                """
                all = set()
                for d in basedir.load_cache_paths(config_site, 'interfaces'):
                        for leaf in os.listdir(d):
                                if not leaf.startswith('.'):
                                        all.add(unescape(leaf))
                for d in basedir.load_config_paths(config_site, config_prog, 'user_overrides'):
                        for leaf in os.listdir(d):
                                if not leaf.startswith('.'):
                                        all.add(unescape(leaf))
                return list(all)        # Why not just return the set?

        def get_icon_path(self, iface):
                """Get the path of a cached icon for an interface.
                @param iface: interface whose icon we want
                @return: the path of the cached icon, or None if not cached.
                @rtype: str"""
                return basedir.load_first_cache(config_site, 'interface_icons',
                                                 escape(iface.uri))

        def get_cached_signatures(self, uri):
                """Verify the cached interface using GPG.
                Only new-style XML-signed interfaces retain their signatures in the cache.
                @param uri: the feed to check
                @type uri: str
                @return: a list of signatures, or None
                @rtype: [L{gpg.Signature}] or None
                @since: 0.25"""
                import gpg
                if uri.startswith('/'):
                        old_iface = uri
                else:
                        old_iface = basedir.load_first_cache(config_site, 'interfaces', escape(uri))
                        if old_iface is None:
                                return None
                try:
                        return gpg.check_stream(file(old_iface))[1]
                except SafeException, ex:
                        debug("No signatures (old-style interface): %s" % ex)
                        return None
        
        def _get_signature_date(self, uri):
                """Read the date-stamp from the signature of the cached interface.
                If the date-stamp is unavailable, returns None."""
                import trust
                sigs = self.get_cached_signatures(uri)
                if sigs:
                        return self._oldest_trusted(sigs, trust.domain_from_url(uri))
        
        def _oldest_trusted(self, sigs, domain):
                """Return the date of the oldest trusted signature in the list, or None if there
                are no trusted sigs in the list."""
                trusted = [s.get_timestamp() for s in sigs if s.is_trusted(domain)]
                if trusted:
                        return min(trusted)
                return None

        def mark_as_checking(self, url):
                """Touch a 'last_check_attempt_timestamp' file for this feed.
                If url is a local path, nothing happens.
                This prevents us from repeatedly trying to download a failing feed many
                times in a short period."""
                if url.startswith('/'):
                        return
                feeds_dir = basedir.save_cache_path(config_site, config_prog, 'last-check-attempt')
                timestamp_path = os.path.join(feeds_dir, model._pretty_escape(url))
                fd = os.open(timestamp_path, os.O_WRONLY | os.O_CREAT, 0644)
                os.close(fd)

        def get_last_check_attempt(self, url):
                """Return the time of the most recent update attempt for a feed.
                @see: L{mark_as_checking}
                @return: The time, or None if none is recorded
                @rtype: float | None"""
                timestamp_path = basedir.load_first_cache(config_site, config_prog, 'last-check-attempt', model._pretty_escape(url))
                if timestamp_path:
                        return os.stat(timestamp_path).st_mtime
                return None

iface_cache = IfaceCache()