Added "mode" to <environment>'s _toxml method

[zeroinstall.git] / zeroinstall / injector / model.py

"""In-memory representation of interfaces and other data structures.

The objects in this module are used to build a representation of an XML interface
file in memory.

@see: L{reader} constructs these data-structures
@see: U{http://0install.net/interface-spec.html} description of the domain model

@var defaults: Default values for the 'default' attribute for <environment> bindings of
well-known variables.
"""

# Copyright (C) 2009, Thomas Leonard
# See the README file for details, or visit http://0install.net.

from zeroinstall import _
import os, re, locale
from logging import info, debug, warn
from zeroinstall import SafeException, version
from zeroinstall.injector.namespaces import XMLNS_IFACE
from zeroinstall.injector import qdom

# Element names for bindings in feed files
binding_names = frozenset(['environment', 'overlay'])

network_offline = 'off-line'
network_minimal = 'minimal'
network_full = 'full'
network_levels = (network_offline, network_minimal, network_full)

stability_levels = {}   # Name -> Stability

defaults = {
        'PATH': '/bin:/usr/bin',
        'XDG_CONFIG_DIRS': '/etc/xdg',
        'XDG_DATA_DIRS': '/usr/local/share:/usr/share',
}

class InvalidInterface(SafeException):
        """Raised when parsing an invalid feed."""
        feed_url = None

        def __init__(self, message, ex = None):
                if ex:
                        try:
                                message += "\n\n(exact error: %s)" % ex
                        except:
                                # Some Python messages have type str but contain UTF-8 sequences.
                                # (e.g. IOException). Adding these to a Unicode 'message' (e.g.
                                # after gettext translation) will cause an error.
                                import codecs
                                decoder = codecs.lookup('utf-8')
                                decex = decoder.decode(str(ex), errors = 'replace')[0]
                                message += "\n\n(exact error: %s)" % decex

                SafeException.__init__(self, message)

        def __unicode__(self):
                if hasattr(SafeException, '__unicode__'):
                        # Python >= 2.6
                        if self.feed_url:
                                return _('%s [%s]') % (SafeException.__unicode__(self), self.feed_url)
                        return SafeException.__unicode__(self)
                else:
                        return unicode(SafeException.__str__(self))

def _split_arch(arch):
        """Split an arch into an (os, machine) tuple. Either or both parts may be None."""
        if not arch:
                return None, None
        elif '-' not in arch:
                raise SafeException(_("Malformed arch '%s'") % arch)
        else:
                osys, machine = arch.split('-', 1)
                if osys == '*': osys = None
                if machine == '*': machine = None
                return osys, machine

def _join_arch(osys, machine):
        if osys == machine == None: return None
        return "%s-%s" % (osys or '*', machine or '*')

def _best_language_match(options):
        (language, encoding) = locale.getlocale()

        if language:
                # xml:lang uses '-', while LANG uses '_'
                language = language.replace('_', '-')
        else:
                language = 'en-US'

        return (options.get(language, None) or                  # Exact match (language+region)
                options.get(language.split('-', 1)[0], None) or # Matching language
                options.get('en', None))                        # English

class Stability(object):
        """A stability rating. Each implementation has an upstream stability rating and,
        optionally, a user-set rating."""
        __slots__ = ['level', 'name', 'description']
        def __init__(self, level, name, description):
                self.level = level
                self.name = name
                self.description = description
                assert name not in stability_levels
                stability_levels[name] = self

        def __cmp__(self, other):
                return cmp(self.level, other.level)

        def __str__(self):
                return self.name

        def __repr__(self):
                return _("<Stability: %s>") % self.description

def process_binding(e):
        """Internal"""
        if e.name == 'environment':
                mode = {
                        None: EnvironmentBinding.PREPEND,
                        'prepend': EnvironmentBinding.PREPEND,
                        'append': EnvironmentBinding.APPEND,
                        'replace': EnvironmentBinding.REPLACE,
                }[e.getAttribute('mode')]
                        
                binding = EnvironmentBinding(e.getAttribute('name'),
                                             insert = e.getAttribute('insert'),
                                             default = e.getAttribute('default'),
                                             value = e.getAttribute('value'),
                                             mode = mode)
                if not binding.name: raise InvalidInterface(_("Missing 'name' in binding"))
                if binding.insert is None and binding.value is None:
                        raise InvalidInterface(_("Missing 'insert' or 'value' in binding"))
                if binding.insert is not None and binding.value is not None:
                        raise InvalidInterface(_("Binding contains both 'insert' and 'value'"))
                return binding
        elif e.name == 'overlay':
                return OverlayBinding(e.getAttribute('src'), e.getAttribute('mount-point'))
        else:
                raise Exception(_("Unknown binding type '%s'") % e.name)

def process_depends(item, local_feed_dir):
        """Internal"""
        # Note: also called from selections
        attrs = item.attrs
        dep_iface = item.getAttribute('interface')
        if not dep_iface:
                raise InvalidInterface(_("Missing 'interface' on <%s>") % item.name)
        if dep_iface.startswith('./'):
                if local_feed_dir:
                        dep_iface = os.path.abspath(os.path.join(local_feed_dir, dep_iface))
                        # (updates the element too, in case we write it out again)
                        attrs['interface'] = dep_iface
                else:
                        raise InvalidInterface(_('Relative interface URI "%s" in non-local feed') % dep_iface)
        dependency = InterfaceDependency(dep_iface, element = item)

        for e in item.childNodes:
                if e.uri != XMLNS_IFACE: continue
                if e.name in binding_names:
                        dependency.bindings.append(process_binding(e))
                elif e.name == 'version':
                        dependency.restrictions.append(
                                VersionRangeRestriction(not_before = parse_version(e.getAttribute('not-before')),
                                                        before = parse_version(e.getAttribute('before'))))
        return dependency

def N_(message): return message

insecure = Stability(0, N_('insecure'), _('This is a security risk'))
buggy = Stability(5, N_('buggy'), _('Known to have serious bugs'))
developer = Stability(10, N_('developer'), _('Work-in-progress - bugs likely'))
testing = Stability(20, N_('testing'), _('Stability unknown - please test!'))
stable = Stability(30, N_('stable'), _('Tested - no serious problems found'))
packaged = Stability(35, N_('packaged'), _('Supplied by the local package manager'))
preferred = Stability(40, N_('preferred'), _('Best of all - must be set manually'))

del N_

class Restriction(object):
        """A Restriction limits the allowed implementations of an Interface."""
        __slots__ = []

        def meets_restriction(self, impl):
                """Called by the L{solver.Solver} to check whether a particular implementation is acceptable.
                @return: False if this implementation is not a possibility
                @rtype: bool
                """
                raise NotImplementedError(_("Abstract"))
        
class VersionRestriction(Restriction):
        """Only select implementations with a particular version number.
        @since: 0.40"""

        def __init__(self, version):
                """@param version: the required version number
                @see: L{parse_version}; use this to pre-process the version number
                """
                self.version = version

        def meets_restriction(self, impl):
                return impl.version == self.version

        def __str__(self):
                return _("(restriction: version = %s)") % format_version(self.version)

class VersionRangeRestriction(Restriction):
        """Only versions within the given range are acceptable"""
        __slots__ = ['before', 'not_before']

        def __init__(self, before, not_before):
                """@param before: chosen versions must be earlier than this
                @param not_before: versions must be at least this high
                @see: L{parse_version}; use this to pre-process the versions
                """
                self.before = before
                self.not_before = not_before
        
        def meets_restriction(self, impl):
                if self.not_before and impl.version < self.not_before:
                        return False
                if self.before and impl.version >= self.before:
                        return False
                return True
        
        def __str__(self):
                if self.not_before is not None or self.before is not None:
                        range = ''
                        if self.not_before is not None:
                                range += format_version(self.not_before) + ' <= '
                        range += 'version'
                        if self.before is not None:
                                range += ' < ' + format_version(self.before)
                else:
                        range = 'none'
                return _("(restriction: %s)") % range

class Binding(object):
        """Information about how the choice of a Dependency is made known
        to the application being run."""

class EnvironmentBinding(Binding):
        """Indicate the chosen implementation using an environment variable."""
        __slots__ = ['name', 'insert', 'default', 'mode', 'value']

        PREPEND = 'prepend'
        APPEND = 'append'
        REPLACE = 'replace'

        def __init__(self, name, insert, default = None, mode = PREPEND, value=None):
                """
                mode argument added in version 0.28
                value argument added in version 0.52
                """
                self.name = name
                self.insert = insert
                self.default = default
                self.mode = mode
                self.value = value
        
        def __str__(self):
                return _("<environ %(name)s %(mode)s %(insert)s %(value)s>") % {'name': self.name,'mode':  self.mode, 'insert': self.insert, 'value': self.value}

        __repr__ = __str__
        
        def get_value(self, path, old_value):
                """Calculate the new value of the environment variable after applying this binding.
                @param path: the path to the selected implementation
                @param old_value: the current value of the environment variable
                @return: the new value for the environment variable"""

                if self.insert is not None:
                        extra = os.path.join(path, self.insert)
                else:
                        assert self.value is not None
                        extra = self.value

                if self.mode == EnvironmentBinding.REPLACE:
                        return extra

                if old_value is None:
                        old_value = self.default or defaults.get(self.name, None)
                if old_value is None:
                        return extra
                if self.mode == EnvironmentBinding.PREPEND:
                        return extra + os.pathsep + old_value
                else:
                        return old_value + os.pathsep + extra

        def _toxml(self, doc):
                """Create a DOM element for this binding.
                @param doc: document to use to create the element
                @return: the new element
                """
                env_elem = doc.createElementNS(XMLNS_IFACE, 'environment')
                env_elem.setAttributeNS(None, 'name', self.name)
                if self.mode is not None:
                        env_elem.setAttributeNS(None, 'mode', self.mode)
                if self.insert is not None:
                        env_elem.setAttributeNS(None, 'insert', self.insert)
                else:
                        env_elem.setAttributeNS(None, 'value', self.value)
                if self.default:
                        env_elem.setAttributeNS(None, 'default', self.default)
                return env_elem

class OverlayBinding(Binding):
        """Make the chosen implementation available by overlaying it onto another part of the file-system.
        This is to support legacy programs which use hard-coded paths."""
        __slots__ = ['src', 'mount_point']

        def __init__(self, src, mount_point):
                self.src = src
                self.mount_point = mount_point

        def __str__(self):
                return _("<overlay %(src)s on %(mount_point)s>") % {'src': self.src or '.', 'mount_point': self.mount_point or '/'}

        __repr__ = __str__

        def _toxml(self, doc):
                """Create a DOM element for this binding.
                @param doc: document to use to create the element
                @return: the new element
                """
                env_elem = doc.createElementNS(XMLNS_IFACE, 'overlay')
                if self.src is not None:
                        env_elem.setAttributeNS(None, 'src', self.src)
                if self.mount_point is not None:
                        env_elem.setAttributeNS(None, 'mount-point', self.mount_point)
                return env_elem

class Feed(object):
        """An interface's feeds are other interfaces whose implementations can also be
        used as implementations of this interface."""
        __slots__ = ['uri', 'os', 'machine', 'user_override', 'langs']
        def __init__(self, uri, arch, user_override, langs = None):
                self.uri = uri
                # This indicates whether the feed comes from the user's overrides
                # file. If true, writer.py will write it when saving.
                self.user_override = user_override
                self.os, self.machine = _split_arch(arch)
                self.langs = langs
        
        def __str__(self):
                return "<Feed from %s>" % self.uri
        __repr__ = __str__

        arch = property(lambda self: _join_arch(self.os, self.machine))

class Dependency(object):
        """A Dependency indicates that an Implementation requires some additional
        code to function. This is an abstract base class.
        @ivar qdom: the XML element for this Dependency (since 0launch 0.51)
        @type qdom: L{qdom.Element}
        @ivar metadata: any extra attributes from the XML element
        @type metadata: {str: str}
        """
        __slots__ = ['qdom']

        def __init__(self, element):
                assert isinstance(element, qdom.Element), type(element) # Use InterfaceDependency instead!
                self.qdom = element

        @property
        def metadata(self):
                return self.qdom.attrs

class InterfaceDependency(Dependency):
        """A Dependency on a Zero Install interface.
        @ivar interface: the interface required by this dependency
        @type interface: str
        @ivar restrictions: a list of constraints on acceptable implementations
        @type restrictions: [L{Restriction}]
        @ivar bindings: how to make the choice of implementation known
        @type bindings: [L{Binding}]
        @since: 0.28
        """
        __slots__ = ['interface', 'restrictions', 'bindings']

        def __init__(self, interface, restrictions = None, element = None):
                Dependency.__init__(self, element)
                assert isinstance(interface, (str, unicode))
                assert interface
                self.interface = interface
                if restrictions is None:
                        self.restrictions = []
                else:
                        self.restrictions = restrictions
                self.bindings = []

        def __str__(self):
                return _("<Dependency on %(interface)s; bindings: %(bindings)s%(restrictions)s>") % {'interface': self.interface, 'bindings': self.bindings, 'restrictions': self.restrictions}

class RetrievalMethod(object):
        """A RetrievalMethod provides a way to fetch an implementation."""
        __slots__ = []

class DownloadSource(RetrievalMethod):
        """A DownloadSource provides a way to fetch an implementation."""
        __slots__ = ['implementation', 'url', 'size', 'extract', 'start_offset', 'type']

        def __init__(self, implementation, url, size, extract, start_offset = 0, type = None):
                self.implementation = implementation
                self.url = url
                self.size = size
                self.extract = extract
                self.start_offset = start_offset
                self.type = type                # MIME type - see unpack.py

class Recipe(RetrievalMethod):
        """Get an implementation by following a series of steps.
        @ivar size: the combined download sizes from all the steps
        @type size: int
        @ivar steps: the sequence of steps which must be performed
        @type steps: [L{RetrievalMethod}]"""
        __slots__ = ['steps']

        def __init__(self):
                self.steps = []
        
        size = property(lambda self: sum([x.size for x in self.steps]))

class DistributionSource(RetrievalMethod):
        """A package that is installed using the distribution's tools (including PackageKit).
        @ivar install: a function to call to install this package
        @type install: (L{handler.Handler}) -> L{tasks.Blocker}
        @ivar package_id: the package name, in a form recognised by the distribution's tools
        @type package_id: str
        @ivar size: the download size in bytes
        @type size: int
        @ivar needs_confirmation: whether the user should be asked to confirm before calling install()
        @type needs_confirmation: bool"""

        __slots__ = ['package_id', 'size', 'install', 'needs_confirmation']

        def __init__(self, package_id, size, install, needs_confirmation = True):
                RetrievalMethod.__init__(self)
                self.package_id = package_id
                self.size = size
                self.install = install
                self.needs_confirmation = needs_confirmation

class Command(object):
        """A Command is a way of running an Implementation as a program."""

        __slots__ = ['qdom', '_depends', '_local_dir', '_runner']

        def __init__(self, qdom, local_dir):
                """@param qdom: the <command> element
                @param local_dir: the directory containing the feed (for relative dependencies), or None if not local
                """
                assert qdom.name == 'command', 'not <command>: %s' % qdom
                self.qdom = qdom
                self._local_dir = local_dir
                self._depends = None

        path = property(lambda self: self.qdom.attrs.get("path", None))

        def _toxml(self, doc, prefixes):
                return self.qdom.toDOM(doc, prefixes)

        @property
        def requires(self):
                if self._depends is None:
                        self._runner = None
                        depends = []
                        for child in self.qdom.childNodes:
                                if child.name == 'requires':
                                        dep = process_depends(child, self._local_dir)
                                        depends.append(dep)
                                elif child.name == 'runner':
                                        if self._runner:
                                                raise InvalidInterface(_("Multiple <runner>s in <command>!"))
                                        dep = process_depends(child, self._local_dir)
                                        depends.append(dep)
                                        self._runner = dep
                        self._depends = depends
                return self._depends

        def get_runner(self):
                self.requires           # (sets _runner)
                return self._runner

class Implementation(object):
        """An Implementation is a package which implements an Interface.
        @ivar download_sources: list of methods of getting this implementation
        @type download_sources: [L{RetrievalMethod}]
        @ivar feed: the feed owning this implementation (since 0.32)
        @type feed: [L{ZeroInstallFeed}]
        @ivar bindings: how to tell this component where it itself is located (since 0.31)
        @type bindings: [Binding]
        @ivar upstream_stability: the stability reported by the packager
        @type upstream_stability: [insecure | buggy | developer | testing | stable | packaged]
        @ivar user_stability: the stability as set by the user
        @type upstream_stability: [insecure | buggy | developer | testing | stable | packaged | preferred]
        @ivar langs: natural languages supported by this package
        @type langs: str
        @ivar requires: interfaces this package depends on
        @type requires: [L{Dependency}]
        @ivar commands: ways to execute as a program
        @type commands: {str: Command}
        @ivar metadata: extra metadata from the feed
        @type metadata: {"[URI ]localName": str}
        @ivar id: a unique identifier for this Implementation
        @ivar version: a parsed version number
        @ivar released: release date
        @ivar local_path: the directory containing this local implementation, or None if it isn't local (id isn't a path)
        @type local_path: str | None
        @ivar requires_root_install: whether the user will need admin rights to use this
        @type requires_root_install: bool
        """

        # Note: user_stability shouldn't really be here

        __slots__ = ['upstream_stability', 'user_stability', 'langs',
                     'requires', 'metadata', 'download_sources', 'commands',
                     'id', 'feed', 'version', 'released', 'bindings', 'machine']

        def __init__(self, feed, id):
                assert id
                self.feed = feed
                self.id = id
                self.user_stability = None
                self.upstream_stability = None
                self.metadata = {}      # [URI + " "] + localName -> value
                self.requires = []
                self.version = None
                self.released = None
                self.download_sources = []
                self.langs = ""
                self.machine = None
                self.bindings = []
                self.commands = {}

        def get_stability(self):
                return self.user_stability or self.upstream_stability or testing
        
        def __str__(self):
                return self.id

        def __repr__(self):
                return "v%s (%s)" % (self.get_version(), self.id)

        def __cmp__(self, other):
                """Newer versions come first"""
                d = cmp(other.version, self.version)
                if d: return d
                # If the version number is the same, just give a stable sort order, and
                # ensure that two different implementations don't compare equal.
                d = cmp(other.feed.url, self.feed.url)
                if d: return d
                return cmp(other.id, self.id)

        def get_version(self):
                """Return the version as a string.
                @see: L{format_version}
                """
                return format_version(self.version)

        arch = property(lambda self: _join_arch(self.os, self.machine))

        os = None
        local_path = None
        digests = None
        requires_root_install = False

        def _get_main(self):
                """"@deprecated: use commands["run"] instead"""
                main = self.commands.get("run", None)
                if main is not None:
                        return main.path
                return None
        def _set_main(self, path):
                """"@deprecated: use commands["run"] instead"""
                if path is None:
                        if "run" in self.commands:
                                del self.commands["run"]
                else:
                        self.commands["run"] = Command(qdom.Element(XMLNS_IFACE, 'command', {'path': path}), None)
        main = property(_get_main, _set_main)

        def is_available(self, stores):
                """Is this Implementation available locally?
                (a local implementation, an installed distribution package, or a cached ZeroInstallImplementation)
                @rtype: bool
                @since: 0.53
                """
                raise NotImplementedError("abstract")

class DistributionImplementation(Implementation):
        """An implementation provided by the distribution. Information such as the version
        comes from the package manager.
        @since: 0.28"""
        __slots__ = ['distro', 'installed']

        def __init__(self, feed, id, distro):
                assert id.startswith('package:')
                Implementation.__init__(self, feed, id)
                self.distro = distro
                self.installed = False

        @property
        def requires_root_install(self):
                return not self.installed

        def is_available(self, stores):
                return self.installed

class ZeroInstallImplementation(Implementation):
        """An implementation where all the information comes from Zero Install.
        @ivar digests: a list of "algorith=value" strings (since 0.45)
        @type digests: [str]
        @since: 0.28"""
        __slots__ = ['os', 'size', 'digests', 'local_path']

        def __init__(self, feed, id, local_path):
                """id can be a local path (string starting with /) or a manifest hash (eg "sha1=XXX")"""
                assert not id.startswith('package:'), id
                Implementation.__init__(self, feed, id)
                self.size = None
                self.os = None
                self.digests = []
                self.local_path = local_path

        # Deprecated
        dependencies = property(lambda self: dict([(x.interface, x) for x in self.requires
                                                   if isinstance(x, InterfaceDependency)]))

        def add_download_source(self, url, size, extract, start_offset = 0, type = None):
                """Add a download source."""
                self.download_sources.append(DownloadSource(self, url, size, extract, start_offset, type))

        def set_arch(self, arch):
                self.os, self.machine = _split_arch(arch)
        arch = property(lambda self: _join_arch(self.os, self.machine), set_arch)

        def is_available(self, stores):
                if self.local_path is not None:
                        return os.path.exists(self.local_path)
                if self.digests:
                        path = stores.lookup_maybe(self.digests)
                        return path is not None
                return False    # (0compile creates fake entries with no digests)

class Interface(object):
        """An Interface represents some contract of behaviour.
        @ivar uri: the URI for this interface.
        @ivar stability_policy: user's configured policy.
        Implementations at this level or higher are preferred.
        Lower levels are used only if there is no other choice.
        """
        __slots__ = ['uri', 'stability_policy', 'extra_feeds']

        implementations = property(lambda self: self._main_feed.implementations)
        name = property(lambda self: self._main_feed.name)
        description = property(lambda self: self._main_feed.description)
        summary = property(lambda self: self._main_feed.summary)
        last_modified = property(lambda self: self._main_feed.last_modified)
        feeds = property(lambda self: self.extra_feeds + self._main_feed.feeds)
        metadata = property(lambda self: self._main_feed.metadata)

        last_checked = property(lambda self: self._main_feed.last_checked)

        def __init__(self, uri):
                assert uri
                if uri.startswith('http:') or uri.startswith('https:') or os.path.isabs(uri):
                        self.uri = uri
                else:
                        raise SafeException(_("Interface name '%s' doesn't start "
                                            "with 'http:' or 'https:'") % uri)
                self.reset()

        def _get_feed_for(self):
                retval = {}
                for key in self._main_feed.feed_for:
                        retval[key] = True
                return retval
        feed_for = property(_get_feed_for)      # Deprecated (used by 0publish)

        def reset(self):
                self.extra_feeds = []
                self.stability_policy = None

        def get_name(self):
                from zeroinstall.injector.iface_cache import iface_cache
                feed = iface_cache.get_feed(self.uri)
                if feed:
                        return feed.get_name()
                return '(' + os.path.basename(self.uri) + ')'
        
        def __repr__(self):
                return _("<Interface %s>") % self.uri
        
        def set_stability_policy(self, new):
                assert new is None or isinstance(new, Stability)
                self.stability_policy = new
        
        def get_feed(self, url):
                #import warnings
                #warnings.warn("use iface_cache.get_feed instead", DeprecationWarning, 2)
                for x in self.extra_feeds:
                        if x.uri == url:
                                return x
                #return self._main_feed.get_feed(url)
                return None
        
        def get_metadata(self, uri, name):
                return self._main_feed.get_metadata(uri, name)

        @property
        def _main_feed(self):
                #import warnings
                #warnings.warn("use the feed instead", DeprecationWarning, 3)
                from zeroinstall.injector import policy
                iface_cache = policy.get_deprecated_singleton_config().iface_cache
                feed = iface_cache.get_feed(self.uri)
                if feed is None:
                        return _dummy_feed
                return feed

def _merge_attrs(attrs, item):
        """Add each attribute of item to a copy of attrs and return the copy.
        @type attrs: {str: str}
        @type item: L{qdom.Element}
        @rtype: {str: str}
        """
        new = attrs.copy()
        for a in item.attrs:
                new[str(a)] = item.attrs[a]
        return new

def _get_long(elem, attr_name):
        val = elem.getAttribute(attr_name)
        if val is not None:
                try:
                        val = int(val)
                except ValueError:
                        raise SafeException(_("Invalid value for integer attribute '%(attribute_name)s': %(value)s") % {'attribute_name': attr_name, 'value': val})
        return val

class ZeroInstallFeed(object):
        """A feed lists available implementations of an interface.
        @ivar url: the URL for this feed
        @ivar implementations: Implementations in this feed, indexed by ID
        @type implementations: {str: L{Implementation}}
        @ivar name: human-friendly name
        @ivar summaries: short textual description (in various languages, since 0.49)
        @type summaries: {str: str}
        @ivar descriptions: long textual description (in various languages, since 0.49)
        @type descriptions: {str: str}
        @ivar last_modified: timestamp on signature
        @ivar last_checked: time feed was last successfully downloaded and updated
        @ivar feeds: list of <feed> elements in this feed
        @type feeds: [L{Feed}]
        @ivar feed_for: interfaces for which this could be a feed
        @type feed_for: set(str)
        @ivar metadata: extra elements we didn't understand
        """
        # _main is deprecated
        __slots__ = ['url', 'implementations', 'name', 'descriptions', 'first_description', 'summaries', 'first_summary', '_package_implementations',
                     'last_checked', 'last_modified', 'feeds', 'feed_for', 'metadata']

        def __init__(self, feed_element, local_path = None, distro = None):
                """Create a feed object from a DOM.
                @param feed_element: the root element of a feed file
                @type feed_element: L{qdom.Element}
                @param local_path: the pathname of this local feed, or None for remote feeds"""
                self.implementations = {}
                self.name = None
                self.summaries = {}     # { lang: str }
                self.first_summary = None
                self.descriptions = {}  # { lang: str }
                self.first_description = None
                self.last_modified = None
                self.feeds = []
                self.feed_for = set()
                self.metadata = []
                self.last_checked = None
                self._package_implementations = []

                if distro is not None:
                        import warnings
                        warnings.warn("distro argument is now ignored", DeprecationWarning, 2)

                if feed_element is None:
                        return                  # XXX subclass?

                assert feed_element.name in ('interface', 'feed'), "Root element should be <interface>, not %s" % feed_element
                assert feed_element.uri == XMLNS_IFACE, "Wrong namespace on root element: %s" % feed_element.uri

                main = feed_element.getAttribute('main')
                #if main: warn("Setting 'main' on the root element is deprecated. Put it on a <group> instead")

                if local_path:
                        self.url = local_path
                        local_dir = os.path.dirname(local_path)
                else:
                        self.url = feed_element.getAttribute('uri')
                        if not self.url:
                                raise InvalidInterface(_("<interface> uri attribute missing"))
                        local_dir = None        # Can't have relative paths

                min_injector_version = feed_element.getAttribute('min-injector-version')
                if min_injector_version:
                        if parse_version(min_injector_version) > parse_version(version):
                                raise InvalidInterface(_("This feed requires version %(min_version)s or later of "
                                                        "Zero Install, but I am only version %(version)s. "
                                                        "You can get a newer version from http://0install.net") %
                                                        {'min_version': min_injector_version, 'version': version})

                for x in feed_element.childNodes:
                        if x.uri != XMLNS_IFACE:
                                self.metadata.append(x)
                                continue
                        if x.name == 'name':
                                self.name = x.content
                        elif x.name == 'description':
                                if self.first_description == None:
                                        self.first_description = x.content
                                self.descriptions[x.attrs.get("http://www.w3.org/XML/1998/namespace lang", 'en')] = x.content
                        elif x.name == 'summary':
                                if self.first_summary == None:
                                        self.first_summary = x.content
                                self.summaries[x.attrs.get("http://www.w3.org/XML/1998/namespace lang", 'en')] = x.content
                        elif x.name == 'feed-for':
                                feed_iface = x.getAttribute('interface')
                                if not feed_iface:
                                        raise InvalidInterface(_('Missing "interface" attribute in <feed-for>'))
                                self.feed_for.add(feed_iface)
                                # Bug report from a Debian/stable user that --feed gets the wrong value.
                                # Can't reproduce (even in a Debian/stable chroot), but add some logging here
                                # in case it happens again.
                                debug(_("Is feed-for %s"), feed_iface)
                        elif x.name == 'feed':
                                feed_src = x.getAttribute('src')
                                if not feed_src:
                                        raise InvalidInterface(_('Missing "src" attribute in <feed>'))
                                if feed_src.startswith('http:') or feed_src.startswith('https:') or local_path:
                                        langs = x.getAttribute('langs')
                                        if langs: langs = langs.replace('_', '-')
                                        self.feeds.append(Feed(feed_src, x.getAttribute('arch'), False, langs = langs))
                                else:
                                        raise InvalidInterface(_("Invalid feed URL '%s'") % feed_src)
                        else:
                                self.metadata.append(x)

                if not self.name:
                        raise InvalidInterface(_("Missing <name> in feed"))
                if not self.summary:
                        raise InvalidInterface(_("Missing <summary> in feed"))

                def process_group(group, group_attrs, base_depends, base_bindings, base_commands):
                        for item in group.childNodes:
                                if item.uri != XMLNS_IFACE: continue

                                if item.name not in ('group', 'implementation', 'package-implementation'):
                                        continue

                                # We've found a group or implementation. Scan for dependencies,
                                # bindings and commands. Doing this here means that:
                                # - We can share the code for groups and implementations here.
                                # - The order doesn't matter, because these get processed first.
                                # A side-effect is that the document root cannot contain
                                # these.

                                depends = base_depends[:]
                                bindings = base_bindings[:]
                                commands = base_commands.copy()

                                for attr, command in [('main', 'run'),
                                                      ('self-test', 'test')]:
                                        value = item.attrs.get(attr, None)
                                        if value is not None:
                                                commands[command] = Command(qdom.Element(XMLNS_IFACE, 'command', {'path': value}), None)

                                for child in item.childNodes:
                                        if child.uri != XMLNS_IFACE: continue
                                        if child.name == 'requires':
                                                dep = process_depends(child, local_dir)
                                                depends.append(dep)
                                        elif child.name == 'command':
                                                command_name = child.attrs.get('name', None)
                                                if not command_name:
                                                        raise InvalidInterface('Missing name for <command>')
                                                commands[command_name] = Command(child, local_dir)
                                        elif child.name in binding_names:
                                                bindings.append(process_binding(child))

                                compile_command = item.attrs.get('http://zero-install.sourceforge.net/2006/namespaces/0compile command')
                                if compile_command is not None:
                                        commands['compile'] = Command(qdom.Element(XMLNS_IFACE, 'command', {'shell-command': compile_command}), None)

                                item_attrs = _merge_attrs(group_attrs, item)

                                if item.name == 'group':
                                        process_group(item, item_attrs, depends, bindings, commands)
                                elif item.name == 'implementation':
                                        process_impl(item, item_attrs, depends, bindings, commands)
                                elif item.name == 'package-implementation':
                                        if depends:
                                                warn("A <package-implementation> with dependencies in %s!", self.url)
                                        self._package_implementations.append((item, item_attrs))
                                else:
                                        assert 0

                def process_impl(item, item_attrs, depends, bindings, commands):
                        id = item.getAttribute('id')
                        if id is None:
                                raise InvalidInterface(_("Missing 'id' attribute on %s") % item)
                        local_path = item_attrs.get('local-path')
                        if local_dir and local_path:
                                abs_local_path = os.path.abspath(os.path.join(local_dir, local_path))
                                impl = ZeroInstallImplementation(self, id, abs_local_path)
                        elif local_dir and (id.startswith('/') or id.startswith('.')):
                                # For old feeds
                                id = os.path.abspath(os.path.join(local_dir, id))
                                impl = ZeroInstallImplementation(self, id, id)
                        else:
                                impl = ZeroInstallImplementation(self, id, None)
                                if '=' in id:
                                        # In older feeds, the ID was the (single) digest
                                        impl.digests.append(id)
                        if id in self.implementations:
                                warn(_("Duplicate ID '%(id)s' in feed '%(feed)s'"), {'id': id, 'feed': self})
                        self.implementations[id] = impl

                        impl.metadata = item_attrs
                        try:
                                version_mod = item_attrs.get('version-modifier', None)
                                if version_mod:
                                        item_attrs['version'] += version_mod
                                        del item_attrs['version-modifier']
                                version = item_attrs['version']
                        except KeyError:
                                raise InvalidInterface(_("Missing version attribute"))
                        impl.version = parse_version(version)

                        impl.commands = commands

                        impl.released = item_attrs.get('released', None)
                        impl.langs = item_attrs.get('langs', '').replace('_', '-')

                        size = item.getAttribute('size')
                        if size:
                                impl.size = int(size)
                        impl.arch = item_attrs.get('arch', None)
                        try:
                                stability = stability_levels[str(item_attrs['stability'])]
                        except KeyError:
                                stab = str(item_attrs['stability'])
                                if stab != stab.lower():
                                        raise InvalidInterface(_('Stability "%s" invalid - use lower case!') % item_attrs.stability)
                                raise InvalidInterface(_('Stability "%s" invalid') % item_attrs['stability'])
                        if stability >= preferred:
                                raise InvalidInterface(_("Upstream can't set stability to preferred!"))
                        impl.upstream_stability = stability

                        impl.bindings = bindings
                        impl.requires = depends

                        for elem in item.childNodes:
                                if elem.uri != XMLNS_IFACE: continue
                                if elem.name == 'archive':
                                        url = elem.getAttribute('href')
                                        if not url:
                                                raise InvalidInterface(_("Missing href attribute on <archive>"))
                                        size = elem.getAttribute('size')
                                        if not size:
                                                raise InvalidInterface(_("Missing size attribute on <archive>"))
                                        impl.add_download_source(url = url, size = int(size),
                                                        extract = elem.getAttribute('extract'),
                                                        start_offset = _get_long(elem, 'start-offset'),
                                                        type = elem.getAttribute('type'))
                                elif elem.name == 'manifest-digest':
                                        for aname, avalue in elem.attrs.iteritems():
                                                if ' ' not in aname:
                                                        impl.digests.append('%s=%s' % (aname, avalue))
                                elif elem.name == 'recipe':
                                        recipe = Recipe()
                                        for recipe_step in elem.childNodes:
                                                if recipe_step.uri == XMLNS_IFACE and recipe_step.name == 'archive':
                                                        url = recipe_step.getAttribute('href')
                                                        if not url:
                                                                raise InvalidInterface(_("Missing href attribute on <archive>"))
                                                        size = recipe_step.getAttribute('size')
                                                        if not size:
                                                                raise InvalidInterface(_("Missing size attribute on <archive>"))
                                                        recipe.steps.append(DownloadSource(None, url = url, size = int(size),
                                                                        extract = recipe_step.getAttribute('extract'),
                                                                        start_offset = _get_long(recipe_step, 'start-offset'),
                                                                        type = recipe_step.getAttribute('type')))
                                                else:
                                                        info(_("Unknown step '%s' in recipe; skipping recipe"), recipe_step.name)
                                                        break
                                        else:
                                                impl.download_sources.append(recipe)

                root_attrs = {'stability': 'testing'}
                root_commands = {}
                if main:
                        info("Note: @main on document element is deprecated in %s", self)
                        root_commands['run'] = Command(qdom.Element(XMLNS_IFACE, 'command', {'path': main}), None)
                process_group(feed_element, root_attrs, [], [], root_commands)
        
        def get_distro_feed(self):
                """Does this feed contain any <pacakge-implementation> elements?
                i.e. is it worth asking the package manager for more information?
                @return: the URL of the virtual feed, or None
                @since: 0.49"""
                if self._package_implementations:
                        return "distribution:" + self.url
                return None

        def get_package_impls(self, distro):
                """Find the best <pacakge-implementation> element(s) for the given distribution.
                @param distro: the distribution to use to rate them
                @type distro: L{distro.Distribution}
                @return: a list of tuples for the best ranked elements
                @rtype: [str]
                @since: 0.49"""
                best_score = 0
                best_impls = []

                for item, item_attrs in self._package_implementations:
                        distro_names = item_attrs.get('distributions', '')
                        for distro_name in distro_names.split(' '):
                                score = distro.get_score(distro_name)
                                if score > best_score:
                                        best_score = score
                                        best_impls = []
                                if score == best_score:
                                        best_impls.append((item, item_attrs))
                return best_impls

        def get_name(self):
                return self.name or '(' + os.path.basename(self.url) + ')'
        
        def __repr__(self):
                return _("<Feed %s>") % self.url
        
        def set_stability_policy(self, new):
                assert new is None or isinstance(new, Stability)
                self.stability_policy = new
        
        def get_feed(self, url):
                for x in self.feeds:
                        if x.uri == url:
                                return x
                return None
        
        def add_metadata(self, elem):
                self.metadata.append(elem)
        
        def get_metadata(self, uri, name):
                """Return a list of interface metadata elements with this name and namespace URI."""
                return [m for m in self.metadata if m.name == name and m.uri == uri]

        @property
        def summary(self):
                return _best_language_match(self.summaries) or self.first_summary

        @property
        def description(self):
                return _best_language_match(self.descriptions) or self.first_description

class DummyFeed(object):
        """Temporary class used during API transition."""
        last_modified = None
        name = '-'
        last_checked = property(lambda self: None)
        implementations = property(lambda self: {})
        feeds = property(lambda self: [])
        summary = property(lambda self: '-')
        description = property(lambda self: '')
        def get_name(self): return self.name
        def get_feed(self, url): return None
        def get_metadata(self, uri, name): return []
_dummy_feed = DummyFeed()

def unescape(uri):
        """Convert each %20 to a space, etc.
        @rtype: str"""
        uri = uri.replace('#', '/')
        if '%' not in uri: return uri
        return re.sub('%[0-9a-fA-F][0-9a-fA-F]',
                lambda match: chr(int(match.group(0)[1:], 16)),
                uri).decode('utf-8')

def escape(uri):
        """Convert each space to %20, etc
        @rtype: str"""
        return re.sub('[^-_.a-zA-Z0-9]',
                lambda match: '%%%02x' % ord(match.group(0)),
                uri.encode('utf-8'))

def _pretty_escape(uri):
        """Convert each space to %20, etc
        : is preserved and / becomes #. This makes for nicer strings,
        and may replace L{escape} everywhere in future.
        @rtype: str"""
        if os.name == "posix":
                # Only preserve : on Posix systems
                preserveRegex = '[^-_.a-zA-Z0-9:/]'
        else:
                # Other OSes may not allow the : character in file names
                preserveRegex = '[^-_.a-zA-Z0-9/]'
        return re.sub(preserveRegex,
                lambda match: '%%%02x' % ord(match.group(0)),
                uri.encode('utf-8')).replace('/', '#')

def canonical_iface_uri(uri):
        """If uri is a relative path, convert to an absolute one.
        A "file:///foo" URI is converted to "/foo".
        An "alias:prog" URI expands to the URI in the 0alias script
        Otherwise, return it unmodified.
        @rtype: str
        @raise SafeException: if uri isn't valid
        """
        if uri.startswith('http://') or uri.startswith('https://'):
                if uri.count("/") < 3:
                        raise SafeException(_("Missing / after hostname in URI '%s'") % uri)
                return uri
        elif uri.startswith('file:///'):
                return uri[7:]
        elif uri.startswith('alias:'):
                from zeroinstall import alias, support
                alias_prog = uri[6:]
                if not os.path.isabs(alias_prog):
                        full_path = support.find_in_path(alias_prog)
                        if not full_path:
                                raise alias.NotAnAliasScript("Not found in $PATH: " + alias_prog)
                else:
                        full_path = alias_prog
                interface_uri, main = alias.parse_script(full_path)
                return interface_uri
        else:
                iface_uri = os.path.realpath(uri)
                if os.path.isfile(iface_uri):
                        return iface_uri
        raise SafeException(_("Bad interface name '%(uri)s'.\n"
                        "(doesn't start with 'http:', and "
                        "doesn't exist as a local file '%(interface_uri)s' either)") %
                        {'uri': uri, 'interface_uri': iface_uri})

_version_mod_to_value = {
        'pre': -2,
        'rc': -1,
        '': 0,
        'post': 1,
}

# Reverse mapping
_version_value_to_mod = {}
for x in _version_mod_to_value: _version_value_to_mod[_version_mod_to_value[x]] = x
del x

_version_re = re.compile('-([a-z]*)')

def parse_version(version_string):
        """Convert a version string to an internal representation.
        The parsed format can be compared quickly using the standard Python functions.
         - Version := DottedList ("-" Mod DottedList?)*
         - DottedList := (Integer ("." Integer)*)
        @rtype: tuple (opaque)
        @raise SafeException: if the string isn't a valid version
        @since: 0.24 (moved from L{reader}, from where it is still available):"""
        if version_string is None: return None
        parts = _version_re.split(version_string)
        if parts[-1] == '':
                del parts[-1]   # Ends with a modifier
        else:
                parts.append('')
        if not parts:
                raise SafeException(_("Empty version string!"))
        l = len(parts)
        try:
                for x in range(0, l, 2):
                        part = parts[x]
                        if part:
                                parts[x] = map(int, parts[x].split('.'))
                        else:
                                parts[x] = []   # (because ''.split('.') == [''], not [])
                for x in range(1, l, 2):
                        parts[x] = _version_mod_to_value[parts[x]]
                return parts
        except ValueError, ex:
                raise SafeException(_("Invalid version format in '%(version_string)s': %(exception)s") % {'version_string': version_string, 'exception': ex})
        except KeyError, ex:
                raise SafeException(_("Invalid version modifier in '%(version_string)s': %(exception)s") % {'version_string': version_string, 'exception': ex})

def format_version(version):
        """Format a parsed version for display. Undoes the effect of L{parse_version}.
        @see: L{Implementation.get_version}
        @rtype: str
        @since: 0.24"""
        version = version[:]
        l = len(version)
        for x in range(0, l, 2):
                version[x] = '.'.join(map(str, version[x]))
        for x in range(1, l, 2):
                version[x] = '-' + _version_value_to_mod[version[x]]
        if version[-1] == '-': del version[-1]
        return ''.join(version)