Radicale/radicale/xmlutils.py

# This file is part of Radicale Server - Calendar Server
# Copyright © 2008 Nicolas Kandel
# Copyright © 2008 Pascal Halter
# Copyright © 2008-2015 Guillaume Ayoub
#
# This library is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with Radicale.  If not, see <http://www.gnu.org/licenses/>.

"""
XML and iCal requests manager.

Note that all these functions need to receive unicode objects for full
iCal requests (PUT) and string objects with charset correctly defined
in them for XML requests (all but PUT).

"""

import copy
import math
import posixpath
import re
import xml.etree.ElementTree as ET
from collections import OrderedDict
from datetime import date, datetime, timedelta, timezone
from http import client
from itertools import chain
from urllib.parse import quote, unquote, urlparse

from . import storage

MIMETYPES = {
    "VADDRESSBOOK": "text/vcard",
    "VCALENDAR": "text/calendar"}

NAMESPACES = {
    "C": "urn:ietf:params:xml:ns:caldav",
    "CR": "urn:ietf:params:xml:ns:carddav",
    "D": "DAV:",
    "CS": "http://calendarserver.org/ns/",
    "ICAL": "http://apple.com/ns/ical/",
    "ME": "http://me.com/_namespace/"}

NAMESPACES_REV = {}
for short, url in NAMESPACES.items():
    NAMESPACES_REV[url] = short
    ET.register_namespace("" if short == "D" else short, url)

CLARK_TAG_REGEX = re.compile(r"{(?P<namespace>[^}]*)}(?P<tag>.*)", re.VERBOSE)
HUMAN_REGEX = re.compile(r"(?P<namespace>[^:{}]*)(?P<tag>.*)", re.VERBOSE)

DAY = timedelta(days=1)
SECOND = timedelta(seconds=1)
DATETIME_MIN = datetime.min.replace(tzinfo=timezone.utc)
DATETIME_MAX = datetime.max.replace(tzinfo=timezone.utc)
TIMESTAMP_MIN = math.floor(DATETIME_MIN.timestamp())
TIMESTAMP_MAX = math.ceil(DATETIME_MAX.timestamp())


class VObjectBugException(Exception):
    """Exception for workarounds related to bugs in VObject."""


def pretty_xml(element, level=0):
    """Indent an ElementTree ``element`` and its children."""
    if not level:
        element = copy.deepcopy(element)
    i = "\n" + level * "  "
    if len(element):
        if not element.text or not element.text.strip():
            element.text = i + "  "
        if not element.tail or not element.tail.strip():
            element.tail = i
        for sub_element in element:
            pretty_xml(sub_element, level + 1)
        if not sub_element.tail or not sub_element.tail.strip():
            sub_element.tail = i
    else:
        if level and (not element.tail or not element.tail.strip()):
            element.tail = i
    if not level:
        return '<?xml version="1.0"?>\n%s' % ET.tostring(element, "unicode")


def _tag(short_name, local):
    """Get XML Clark notation {uri(``short_name``)}``local``."""
    return "{%s}%s" % (NAMESPACES[short_name], local)


def _tag_from_clark(name):
    """Get a human-readable variant of the XML Clark notation tag ``name``.

    For a given name using the XML Clark notation, return a human-readable
    variant of the tag name for known namespaces. Otherwise, return the name as
    is.

    """
    match = CLARK_TAG_REGEX.match(name)
    if match and match.group("namespace") in NAMESPACES_REV:
        args = {
            "ns": NAMESPACES_REV[match.group("namespace")],
            "tag": match.group("tag")}
        return "%(ns)s:%(tag)s" % args
    return name


def _tag_from_human(name):
    """Get an XML Clark notation tag from human-readable variant ``name``."""
    match = HUMAN_REGEX.match(name)
    if match and match.group("namespace") in NAMESPACES:
        return _tag(match.group("namespace"), match.group("tag"))
    return name


def _response(code):
    """Return full W3C names from HTTP status codes."""
    return "HTTP/1.1 %i %s" % (code, client.responses[code])


def _href(base_prefix, href):
    """Return prefixed href."""
    return quote("%s%s" % (base_prefix, href))


def _webdav_error(namespace, name):
    """Generate XML error message."""
    root = ET.Element(_tag("D", "error"))
    root.append(ET.Element(_tag(namespace, name)))
    return root


def _date_to_datetime(date_):
    """Transform a date to a UTC datetime.

    If date_ is a datetime without timezone, return as UTC datetime. If date_
    is already a datetime with timezone, return as is.

    """
    if not isinstance(date_, datetime):
        date_ = datetime.combine(date_, datetime.min.time())
    if not date_.tzinfo:
        date_ = date_.replace(tzinfo=timezone.utc)
    return date_


def _comp_match(item, filter_, scope="collection"):
    """Check whether the ``item`` matches the comp ``filter_``.

    If ``scope`` is ``"collection"``, the filter is applied on the
    item's collection. Otherwise, it's applied on the item.

    See rfc4791-9.7.1.

    """
    filter_length = len(filter_)
    if scope == "collection":
        tag = item.collection.get_meta("tag")
    else:
        for component in item.components():
            if component.name in ("VTODO", "VEVENT", "VJOURNAL"):
                tag = component.name
                break
        else:
            return False
    if filter_length == 0:
        # Point #1 of rfc4791-9.7.1
        return filter_.get("name") == tag
    else:
        if filter_length == 1:
            if filter_[0].tag == _tag("C", "is-not-defined"):
                # Point #2 of rfc4791-9.7.1
                return filter_.get("name") != tag
        if filter_[0].tag == _tag("C", "time-range"):
            # Point #3 of rfc4791-9.7.1
            if not _time_range_match(item.item, filter_[0], tag):
                return False
            filter_ = filter_[1:]
        # Point #4 of rfc4791-9.7.1
        return all(
            _prop_match(item, child) if child.tag == _tag("C", "prop-filter")
            else _comp_match(item, child, scope="component")
            for child in filter_)


def _prop_match(item, filter_):
    """Check whether the ``item`` matches the prop ``filter_``.

    See rfc4791-9.7.2 and rfc6352-10.5.1.

    """
    filter_length = len(filter_)
    if item.collection.get_meta("tag") == "VCALENDAR":
        for component in item.components():
            if component.name in ("VTODO", "VEVENT", "VJOURNAL"):
                vobject_item = component
                break
    else:
        vobject_item = item.item
    if filter_length == 0:
        # Point #1 of rfc4791-9.7.2
        return filter_.get("name").lower() in vobject_item.contents
    else:
        name = filter_.get("name").lower()
        if filter_length == 1:
            if filter_[0].tag == _tag("C", "is-not-defined"):
                # Point #2 of rfc4791-9.7.2
                return name not in vobject_item.contents
        if filter_[0].tag == _tag("C", "time-range"):
            # Point #3 of rfc4791-9.7.2
            if not _time_range_match(vobject_item, filter_[0], name):
                return False
            filter_ = filter_[1:]
        elif filter_[0].tag == _tag("C", "text-match"):
            # Point #4 of rfc4791-9.7.2
            if not _text_match(vobject_item, filter_[0], name):
                return False
            filter_ = filter_[1:]
        return all(
            _param_filter_match(vobject_item, param_filter, name)
            for param_filter in filter_)


def _time_range_match(vobject_item, filter_, child_name):
    """Check whether the component/property ``child_name`` of
       ``vobject_item`` matches the time-range ``filter_``."""

    start = filter_.get("start")
    end = filter_.get("end")
    if not start and not end:
        return False
    if start:
        start = datetime.strptime(start, "%Y%m%dT%H%M%SZ")
    else:
        start = datetime.min
    if end:
        end = datetime.strptime(end, "%Y%m%dT%H%M%SZ")
    else:
        end = datetime.max
    start = start.replace(tzinfo=timezone.utc)
    end = end.replace(tzinfo=timezone.utc)

    matched = False

    def range_fn(range_start, range_end):
        nonlocal matched
        if start < range_end and range_start < end:
            matched = True
            return True
        if end < range_start:
            return True
        return False

    def infinity_fn(start):
        return False

    _visit_time_ranges(vobject_item, child_name, range_fn, infinity_fn)
    return matched


def _visit_time_ranges(vobject_item, child_name, range_fn, infinity_fn):
    """Visit all time ranges in the component/property ``child_name`` of
    `vobject_item`` with visitors ``range_fn`` and ``infinity_fn``.

    ``range_fn`` gets called for every time_range with ``start`` and ``end``
    datetimes as arguments. If the function returns True, the operation is
    cancelled.

    ``infinity_fn`` gets called when an infiite recurrence rule is detected
    with ``start`` datetime as argument. If the function returns True, the
    operation is cancelled.

    See rfc4791-9.9.

    """
    child = getattr(vobject_item, child_name.lower())

    # TODO: Recurrences specified with RDATE
    # (http://www.kanzaki.com/docs/ical/rdate.html) don't seem to work
    # correct in VObject. getrruleset(addRDate=True) returns an empty generator
    # if they are used.
    # TODO: Single recurrences can be overwritten by components with
    # RECURRENCE-ID (http://www.kanzaki.com/docs/ical/recurrenceId.html). They
    # may overwrite the start and end time. Currently these components and
    # the overwritten recurrences are both considered. The overwritten
    # recurrence should be ignored instead.

    def getrruleset(child):
        try:
            first_dtstart = next(iter(child.getrruleset(addRDate=True)),
                                 None)
        except TypeError as e:
            raise VObjectBugException(
                "failed to call getrruleset: %s" % e) from e
        if first_dtstart is None:
            raise VObjectBugException(
                "empty iterator from getrruleset")
        if (hasattr(child, "rrule") and
                ";UNTIL=" not in child.rrule.value.upper() and
                ";COUNT=" not in child.rrule.value.upper()):
            if infinity_fn(_date_to_datetime(first_dtstart)):
                return (), True
        return child.getrruleset(addRDate=True), False

    # Comments give the lines in the tables of the specification
    if child_name == "VEVENT":
        for child in vobject_item.vevent_list:
            # TODO: check if there's a timezone
            dtstart = child.dtstart.value

            if child.rruleset:
                dtstarts, infinity = getrruleset(child)
                if infinity:
                    return
            else:
                dtstarts = (dtstart,)

            dtend = getattr(child, "dtend", None)
            if dtend is not None:
                dtend = dtend.value
                original_duration = (dtend - dtstart).total_seconds()
                dtend = _date_to_datetime(dtend)

            duration = getattr(child, "duration", None)
            if duration is not None:
                original_duration = duration = duration.value

            for dtstart in dtstarts:
                dtstart_is_datetime = isinstance(dtstart, datetime)
                dtstart = _date_to_datetime(dtstart)

                if dtend is not None:
                    # Line 1
                    dtend = dtstart + timedelta(seconds=original_duration)
                    if range_fn(dtstart, dtend):
                        return
                elif duration is not None:
                    if original_duration is None:
                        original_duration = duration.seconds
                    if duration.seconds > 0:
                        # Line 2
                        if range_fn(dtstart, dtstart + duration):
                            return
                    else:
                        # Line 3
                        if range_fn(dtstart, dtstart + SECOND):
                            return
                elif dtstart_is_datetime:
                    # Line 4
                    if range_fn(dtstart, dtstart + SECOND):
                        return
                else:
                    # Line 5
                    if range_fn(dtstart, dtstart + DAY):
                        return

    elif child_name == "VTODO":
        for child in vobject_item.vtodo_list:
            dtstart = getattr(child, "dtstart", None)
            duration = getattr(child, "duration", None)
            due = getattr(child, "due", None)
            completed = getattr(child, "completed", None)
            created = getattr(child, "created", None)

            if dtstart is not None:
                dtstart = _date_to_datetime(dtstart.value)
            if duration is not None:
                duration = duration.value
            if due is not None:
                due = _date_to_datetime(due.value)
                if dtstart is not None:
                    original_duration = (due - dtstart).total_seconds()
            if completed is not None:
                completed = _date_to_datetime(completed.value)
                if created is not None:
                    created = _date_to_datetime(created.value)
                    original_duration = (completed - created).total_seconds()
            elif created is not None:
                created = _date_to_datetime(created.value)

            if child.rruleset:
                reference_dates, infinity = getrruleset(child)
                if infinity:
                    return
            else:
                if dtstart is not None:
                    reference_dates = (dtstart,)
                elif due is not None:
                    reference_dates = (due,)
                elif completed is not None:
                    reference_dates = (completed,)
                elif created is not None:
                    reference_dates = (created,)
                else:
                    # Line 8
                    if range_fn(DATETIME_MIN, DATETIME_MAX):
                        return
                    reference_dates = ()

            for reference_date in reference_dates:
                reference_date = _date_to_datetime(reference_date)

                if dtstart is not None and duration is not None:
                    # Line 1
                    if range_fn(reference_date,
                                reference_date + duration + SECOND):
                        return
                    if range_fn(reference_date + duration - SECOND,
                                reference_date + duration + SECOND):
                        return
                elif dtstart is not None and due is not None:
                    # Line 2
                    due = reference_date + timedelta(seconds=original_duration)
                    if (range_fn(reference_date, due) or
                            range_fn(reference_date,
                                     reference_date + SECOND) or
                            range_fn(due - SECOND, due) or
                            range_fn(due - SECOND, reference_date + SECOND)):
                        return
                elif dtstart is not None:
                    if range_fn(reference_date, reference_date + SECOND):
                        return
                elif due is not None:
                    # Line 4
                    if range_fn(reference_date - SECOND, reference_date):
                        return
                elif completed is not None and created is not None:
                    # Line 5
                    completed = reference_date + timedelta(
                        seconds=original_duration)
                    if (range_fn(reference_date - SECOND,
                                 reference_date + SECOND) or
                            range_fn(completed - SECOND, completed + SECOND) or
                            range_fn(reference_date - SECOND,
                                     reference_date + SECOND) or
                            range_fn(completed - SECOND, completed + SECOND)):
                        return
                elif completed is not None:
                    # Line 6
                    if range_fn(reference_date - SECOND,
                                reference_date + SECOND):
                                return
                elif created is not None:
                    # Line 7
                    if range_fn(reference_date, DATETIME_MAX):
                        return

    elif child_name == "VJOURNAL":
        for child in vobject_item.vjournal_list:
            dtstart = getattr(child, "dtstart", None)

            if dtstart is not None:
                dtstart = dtstart.value
                if child.rruleset:
                    dtstarts, infinity = getrruleset(child)
                    if infinity:
                        return
                else:
                    dtstarts = (dtstart,)

                for dtstart in dtstarts:
                    dtstart_is_datetime = isinstance(dtstart, datetime)
                    dtstart = _date_to_datetime(dtstart)

                    if dtstart_is_datetime:
                        # Line 1
                        if range_fn(dtstart, dtstart + SECOND):
                            return
                    else:
                        # Line 2
                        if range_fn(dtstart, dtstart + DAY):
                            return

    elif isinstance(child, date):
        if range_fn(child, child + DAY):
            return
    elif isinstance(child, datetime):
        if range_fn(child, child + SECOND):
            return


def _text_match(vobject_item, filter_, child_name, attrib_name=None):
    """Check whether the ``item`` matches the text-match ``filter_``.

    See rfc4791-9.7.5.

    """
    # TODO: collations are not supported, but the default ones needed
    # for DAV servers are actually pretty useless. Texts are lowered to
    # be case-insensitive, almost as the "i;ascii-casemap" value.
    match = next(filter_.itertext()).lower()
    children = getattr(vobject_item, "%s_list" % child_name, [])
    if attrib_name:
        condition = any(
            match in attrib.lower() for child in children
            for attrib in child.params.get(attrib_name, []))
    else:
        condition = any(match in child.value.lower() for child in children)
    if filter_.get("negate-condition") == "yes":
        return not condition
    else:
        return condition


def _param_filter_match(vobject_item, filter_, parent_name):
    """Check whether the ``item`` matches the param-filter ``filter_``.

    See rfc4791-9.7.3.

    """
    name = filter_.get("name")
    children = getattr(vobject_item, "%s_list" % parent_name, [])
    condition = any(name in child.params for child in children)
    if len(filter_):
        if filter_[0].tag == _tag("C", "text-match"):
            return condition and _text_match(
                vobject_item, filter_[0], parent_name, name)
        elif filter_[0].tag == _tag("C", "is-not-defined"):
            return not condition
    else:
        return condition


def simplify_prefilters(filters):
    """Creates a simplified condition from ``filters``.

    Returns a tuple (``tag``, ``start``, ``end``, ``simple``) where ``tag`` is
    a string or None (match all) and ``start`` and ``end`` are POSIX
    timestamps (as int). ``simple`` is a bool that indicates that ``filters``
    and the simplified condition are identical.

    """
    flat_filters = tuple(chain.from_iterable(filters))
    simple = len(flat_filters) <= 1
    for col_filter in flat_filters:
        if (col_filter.tag != _tag("C", "comp-filter") or
                col_filter.get("name") != "VCALENDAR"):
            simple = False
            continue
        simple &= len(col_filter) <= 1
        for comp_filter in col_filter:
            if comp_filter.tag != _tag("C", "comp-filter"):
                simple = False
                continue
            tag = comp_filter.get("name")
            if (tag not in ("VTODO", "VEVENT", "VJOURNAL") or comp_filter.find(
                    _tag("C", "is-not-defined")) is not None):
                simple = False
                continue
            simple &= len(comp_filter) <= 1
            for time_filter in comp_filter:
                if time_filter.tag != _tag("C", "time-range"):
                    simple = False
                    continue
                start = time_filter.get("start")
                end = time_filter.get("end")
                if start:
                    start = math.floor(datetime.strptime(
                        start, "%Y%m%dT%H%M%SZ").replace(
                            tzinfo=timezone.utc).timestamp())
                else:
                    start = TIMESTAMP_MIN
                if end:
                    end = math.ceil(datetime.strptime(
                        end, "%Y%m%dT%H%M%SZ").replace(
                            tzinfo=timezone.utc).timestamp())
                else:
                    end = TIMESTAMP_MAX
                return tag, start, end, simple
            return tag, TIMESTAMP_MIN, TIMESTAMP_MAX, simple
    return None, TIMESTAMP_MIN, TIMESTAMP_MAX, simple


def find_tag_and_time_range(vobject_item):
    """Find tag and enclosing time range from ``vobject item``.

    Returns a tuple (``tag``, ``start``, ``end``) where ``tag`` is a string
    and ``start`` and ``end`` are POSIX timestamps (as int).

    This is intened to be used for matching against simplified prefilters.

    """
    tag = ""
    if vobject_item.name == "VCALENDAR":
        for component in vobject_item.components():
            if component.name in ("VTODO", "VEVENT", "VJOURNAL"):
                tag = component.name
                break
    if not tag:
        return (None, math.floor(DATETIME_MIN.timestamp()),
                math.ceil(DATETIME_MAX.timestamp()))
    start = end = None

    def range_fn(range_start, range_end):
        nonlocal start, end
        if start is None or range_start < start:
            start = range_start
        if end is None or end < range_end:
            end = range_end
        return False

    def infinity_fn(range_start):
        nonlocal start, end
        if start is None or range_start < start:
            start = range_start
        end = DATETIME_MAX
        return True

    _visit_time_ranges(vobject_item, tag, range_fn, infinity_fn)
    if start is None:
        start = DATETIME_MIN
    if end is None:
        end = DATETIME_MAX
    return tag, math.floor(start.timestamp()), math.ceil(end.timestamp())


def name_from_path(path, collection):
    """Return Radicale item name from ``path``."""
    path = path.strip("/") + "/"
    start = collection.path + "/"
    if not path.startswith(start):
        raise ValueError("%r doesn't start with %r" % (path, start))
    name = path[len(start):][:-1]
    if name and not storage.is_safe_path_component(name):
        raise ValueError("%r is not a component in collection %r" %
                         (name, collection.path))
    return name


def props_from_request(xml_request, actions=("set", "remove")):
    """Return a list of properties as a dictionary."""
    result = OrderedDict()
    if xml_request is None:
        return result

    for action in actions:
        action_element = xml_request.find(_tag("D", action))
        if action_element is not None:
            break
    else:
        action_element = xml_request

    prop_element = action_element.find(_tag("D", "prop"))
    if prop_element is not None:
        for prop in prop_element:
            if prop.tag == _tag("D", "resourcetype"):
                for resource_type in prop:
                    if resource_type.tag == _tag("C", "calendar"):
                        result["tag"] = "VCALENDAR"
                        break
                    elif resource_type.tag == _tag("CR", "addressbook"):
                        result["tag"] = "VADDRESSBOOK"
                        break
            elif prop.tag == _tag("C", "supported-calendar-component-set"):
                result[_tag_from_clark(prop.tag)] = ",".join(
                    supported_comp.attrib["name"]
                    for supported_comp in prop
                    if supported_comp.tag == _tag("C", "comp"))
            else:
                result[_tag_from_clark(prop.tag)] = prop.text

    return result


def delete(base_prefix, path, collection, href=None):
    """Read and answer DELETE requests.

    Read rfc4918-9.6 for info.

    """
    collection.delete(href)

    multistatus = ET.Element(_tag("D", "multistatus"))
    response = ET.Element(_tag("D", "response"))
    multistatus.append(response)

    href = ET.Element(_tag("D", "href"))
    href.text = _href(base_prefix, path)
    response.append(href)

    status = ET.Element(_tag("D", "status"))
    status.text = _response(200)
    response.append(status)

    return multistatus


def propfind(base_prefix, path, xml_request, read_collections,
             write_collections, user):
    """Read and answer PROPFIND requests.

    Read rfc4918-9.1 for info.

    The collections parameter is a list of collections that are to be included
    in the output.

    """
    # A client may choose not to submit a request body.  An empty PROPFIND
    # request body MUST be treated as if it were an 'allprop' request.
    top_tag = (xml_request[0] if xml_request is not None else
               ET.Element(_tag("D", "allprop")))

    props = ()
    if top_tag.tag == _tag("D", "allprop"):
        props = [
            _tag("D", "getcontenttype"),
            _tag("D", "resourcetype"),
            _tag("D", "displayname"),
            _tag("D", "owner"),
            _tag("D", "getetag"),
            _tag("ICAL", "calendar-color"),
            _tag("CS", "getctag"),
            _tag("C", "supported-calendar-component-set"),
            _tag("D", "supported-report-set"),
        ]
    elif top_tag.tag == _tag("D", "prop"):
        props = [prop.tag for prop in top_tag]

    if _tag("D", "current-user-principal") in props and not user:
        # Ask for authentication
        # Returning the DAV:unauthenticated pseudo-principal as specified in
        # RFC 5397 doesn't seem to work with DAVdroid.
        return client.FORBIDDEN, None

    # Writing answer
    multistatus = ET.Element(_tag("D", "multistatus"))

    collections = []
    for collection in write_collections:
        collections.append(collection)
        if top_tag.tag == _tag("D", "propname"):
            response = _propfind_response(
                base_prefix, path, collection, (), user, write=True,
                propnames=True)
        else:
            response = _propfind_response(
                base_prefix, path, collection, props, user, write=True)
        if response:
            multistatus.append(response)
    for collection in read_collections:
        if collection in collections:
            continue
        if top_tag.tag == _tag("D", "propname"):
            response = _propfind_response(
                base_prefix, path, collection, (), user, write=False,
                propnames=True)
        else:
            response = _propfind_response(
                base_prefix, path, collection, props, user, write=False)
        if response:
            multistatus.append(response)

    return client.MULTI_STATUS, multistatus


def _propfind_response(base_prefix, path, item, props, user, write=False,
                       propnames=False):
    """Build and return a PROPFIND response."""
    is_collection = isinstance(item, storage.BaseCollection)
    if is_collection:
        is_leaf = item.get_meta("tag") in ("VADDRESSBOOK", "VCALENDAR")
        collection = item
    else:
        collection = item.collection

    response = ET.Element(_tag("D", "response"))

    href = ET.Element(_tag("D", "href"))
    if is_collection:
        # Some clients expect collections to end with /
        uri = "/%s/" % item.path if item.path else "/"
    else:
        uri = "/" + posixpath.join(collection.path, item.href)

    href.text = _href(base_prefix, uri)
    response.append(href)

    propstat404 = ET.Element(_tag("D", "propstat"))
    propstat200 = ET.Element(_tag("D", "propstat"))
    response.append(propstat200)

    prop200 = ET.Element(_tag("D", "prop"))
    propstat200.append(prop200)

    prop404 = ET.Element(_tag("D", "prop"))
    propstat404.append(prop404)

    if propnames:
        # Should list all properties that can be retrieved by the code below
        prop200.append(ET.Element(_tag("D", "getetag")))
        prop200.append(ET.Element(_tag("D", "principal-URL")))
        prop200.append(ET.Element(_tag("D", "principal-collection-set")))
        prop200.append(ET.Element(_tag("C", "calendar-user-address-set")))
        prop200.append(ET.Element(_tag("CR", "addressbook-home-set")))
        prop200.append(ET.Element(_tag("C", "calendar-home-set")))
        prop200.append(ET.Element(
            _tag("C", "supported-calendar-component-set")))
        prop200.append(ET.Element(_tag("D", "current-user-privilege-set")))
        prop200.append(ET.Element(_tag("D", "supported-report-set")))
        prop200.append(ET.Element(_tag("D", "getcontenttype")))
        prop200.append(ET.Element(_tag("D", "resourcetype")))

        if is_collection:
            prop200.append(ET.Element(_tag("CS", "getctag")))
            prop200.append(ET.Element(_tag("D", "sync-token")))
            prop200.append(ET.Element(_tag("C", "calendar-timezone")))
            prop200.append(ET.Element(_tag("D", "displayname")))
            prop200.append(ET.Element(_tag("ICAL", "calendar-color")))
            prop200.append(ET.Element(_tag("D", "owner")))

            if is_leaf:
                meta = item.get_meta()
                for tag in meta:
                    clark_tag = _tag_from_human(tag)
                    if prop200.find(clark_tag) is None:
                        prop200.append(ET.Element(clark_tag))

    for tag in props:
        element = ET.Element(tag)
        is404 = False
        if tag == _tag("D", "getetag"):
            element.text = item.etag
        elif tag == _tag("D", "getlastmodified"):
            element.text = item.last_modified
        elif tag == _tag("D", "principal-collection-set"):
            tag = ET.Element(_tag("D", "href"))
            tag.text = _href(base_prefix, "/")
            element.append(tag)
        elif (tag in (_tag("C", "calendar-user-address-set"),
                      _tag("D", "principal-URL"),
                      _tag("CR", "addressbook-home-set"),
                      _tag("C", "calendar-home-set")) and
                collection.is_principal and is_collection):
            tag = ET.Element(_tag("D", "href"))
            tag.text = _href(base_prefix, path)
            element.append(tag)
        elif tag == _tag("C", "supported-calendar-component-set"):
            human_tag = _tag_from_clark(tag)
            if is_collection and is_leaf:
                meta = item.get_meta(human_tag)
                if meta:
                    components = meta.split(",")
                else:
                    components = ("VTODO", "VEVENT", "VJOURNAL")
                for component in components:
                    comp = ET.Element(_tag("C", "comp"))
                    comp.set("name", component)
                    element.append(comp)
            else:
                is404 = True
        elif tag == _tag("D", "current-user-principal"):
            tag = ET.Element(_tag("D", "href"))
            tag.text = _href(base_prefix, ("/%s/" % user) if user else "/")
            element.append(tag)
        elif tag == _tag("D", "current-user-privilege-set"):
            privileges = [("D", "read")]
            if write:
                privileges.append(("D", "all"))
                privileges.append(("D", "write"))
                privileges.append(("D", "write-properties"))
                privileges.append(("D", "write-content"))
            for ns, privilege_name in privileges:
                privilege = ET.Element(_tag("D", "privilege"))
                privilege.append(ET.Element(_tag(ns, privilege_name)))
                element.append(privilege)
        elif tag == _tag("D", "supported-report-set"):
            # These 3 reports are not implemented
            reports = [
                ("D", "expand-property"),
                ("D", "principal-search-property-set"),
                ("D", "principal-property-search")]
            if is_collection and is_leaf:
                reports.append(("D", "sync-collection"))
                if item.get_meta("tag") == "VADDRESSBOOK":
                    reports.append(("CR", "addressbook-multiget"))
                    reports.append(("CR", "addressbook-query"))
                elif item.get_meta("tag") == "VCALENDAR":
                    reports.append(("C", "calendar-multiget"))
                    reports.append(("C", "calendar-query"))
            for ns, report_name in reports:
                supported = ET.Element(_tag("D", "supported-report"))
                report_tag = ET.Element(_tag("D", "report"))
                supported_report_tag = ET.Element(_tag(ns, report_name))
                report_tag.append(supported_report_tag)
                supported.append(report_tag)
                element.append(supported)
        elif is_collection:
            if tag == _tag("D", "getcontenttype"):
                if is_leaf:
                    element.text = MIMETYPES[item.get_meta("tag")]
                else:
                    is404 = True
            elif tag == _tag("D", "resourcetype"):
                if item.is_principal:
                    tag = ET.Element(_tag("D", "principal"))
                    element.append(tag)
                if is_leaf:
                    if item.get_meta("tag") == "VADDRESSBOOK":
                        tag = ET.Element(_tag("CR", "addressbook"))
                        element.append(tag)
                    elif item.get_meta("tag") == "VCALENDAR":
                        tag = ET.Element(_tag("C", "calendar"))
                        element.append(tag)
                tag = ET.Element(_tag("D", "collection"))
                element.append(tag)
            elif tag == _tag("D", "owner"):
                if is_leaf and item.owner:
                    element.text = "/%s/" % item.owner
                else:
                    is404 = True
            elif tag == _tag("D", "displayname"):
                if is_leaf:
                    element.text = item.get_meta("D:displayname") or item.path
                else:
                    is404 = True
            elif tag == _tag("CS", "getctag"):
                if is_leaf:
                    element.text = item.etag
                else:
                    is404 = True
            elif tag == _tag("D", "sync-token"):
                if is_leaf:
                    element.text, _ = item.sync()
                else:
                    is404 = True
            else:
                human_tag = _tag_from_clark(tag)
                meta = item.get_meta(human_tag)
                if meta:
                    element.text = meta
                else:
                    is404 = True
        # Not for collections
        elif tag == _tag("D", "getcontenttype"):
            name = item.name.lower()
            mimetype = "text/vcard" if name == "vcard" else "text/calendar"
            element.text = "%s; component=%s" % (mimetype, name)
        elif tag == _tag("D", "resourcetype"):
            # resourcetype must be returned empty for non-collection elements
            pass
        elif tag == _tag("D", "getcontentlength"):
            encoding = collection.configuration.get("encoding", "request")
            element.text = str(len(item.serialize().encode(encoding)))
        else:
            is404 = True

        if is404:
            prop404.append(element)
        else:
            prop200.append(element)

    status200 = ET.Element(_tag("D", "status"))
    status200.text = _response(200)
    propstat200.append(status200)

    status404 = ET.Element(_tag("D", "status"))
    status404.text = _response(404)
    propstat404.append(status404)
    if len(prop404):
        response.append(propstat404)

    return response


def _add_propstat_to(element, tag, status_number):
    """Add a PROPSTAT response structure to an element.

    The PROPSTAT answer structure is defined in rfc4918-9.1. It is added to the
    given ``element``, for the following ``tag`` with the given
    ``status_number``.

    """
    propstat = ET.Element(_tag("D", "propstat"))
    element.append(propstat)

    prop = ET.Element(_tag("D", "prop"))
    propstat.append(prop)

    clark_tag = tag if "{" in tag else _tag(*tag.split(":", 1))
    prop_tag = ET.Element(clark_tag)
    prop.append(prop_tag)

    status = ET.Element(_tag("D", "status"))
    status.text = _response(status_number)
    propstat.append(status)


def proppatch(base_prefix, path, xml_request, collection):
    """Read and answer PROPPATCH requests.

    Read rfc4918-9.2 for info.

    """
    props_to_set = props_from_request(xml_request, actions=("set",))
    props_to_remove = props_from_request(xml_request, actions=("remove",))

    multistatus = ET.Element(_tag("D", "multistatus"))
    response = ET.Element(_tag("D", "response"))
    multistatus.append(response)

    href = ET.Element(_tag("D", "href"))
    href.text = _href(base_prefix, path)
    response.append(href)

    for short_name in props_to_remove:
        props_to_set[short_name] = ""
    collection.set_meta(props_to_set)

    for short_name in props_to_set:
        _add_propstat_to(response, short_name, 200)

    return multistatus


def report(base_prefix, path, xml_request, collection):
    """Read and answer REPORT requests.

    Read rfc3253-3.6 for info.

    """
    multistatus = ET.Element(_tag("D", "multistatus"))
    if xml_request is None:
        return client.MULTI_STATUS, multistatus
    root = xml_request
    if root.tag in (
            _tag("D", "principal-search-property-set"),
            _tag("D", "principal-property-search"),
            _tag("D", "expand-property")):
        # We don't support searching for principals or indirect retrieving of
        # properties, just return an empty result.
        # InfCloud asks for expand-property reports (even if we don't announce
        # support for them) and stops working if an error code is returned.
        collection.logger.warning("Unsupported REPORT method %r on %r "
                                  "requested", root.tag, path)
        return client.MULTI_STATUS, multistatus
    prop_element = root.find(_tag("D", "prop"))
    props = (
        [prop.tag for prop in prop_element]
        if prop_element is not None else [])

    if root.tag in (
            _tag("C", "calendar-multiget"),
            _tag("CR", "addressbook-multiget")):
        # Read rfc4791-7.9 for info
        hreferences = set()
        for href_element in root.findall(_tag("D", "href")):
            href_path = storage.sanitize_path(
                unquote(urlparse(href_element.text).path))
            if (href_path + "/").startswith(base_prefix + "/"):
                hreferences.add(href_path[len(base_prefix):])
            else:
                collection.logger.warning("Skipping invalid path %r in REPORT "
                                          "request on %r", href_path, path)
    elif root.tag == _tag("D", "sync-collection"):
        old_sync_token_element = root.find(_tag("D", "sync-token"))
        old_sync_token = ""
        if old_sync_token_element is not None and old_sync_token_element.text:
            old_sync_token = old_sync_token_element.text.strip()
        collection.logger.debug("Client provided sync token: %r",
                                old_sync_token)
        try:
            sync_token, names = collection.sync(old_sync_token)
        except ValueError as e:
            # Invalid sync token
            collection.logger.warning("Client provided invalid sync token %r: "
                                      "%s", old_sync_token, e, exc_info=True)
            return (client.PRECONDITION_FAILED,
                    _webdav_error("D", "valid-sync-token"))
        hreferences = ("/" + posixpath.join(collection.path, n) for n in names)
        # Append current sync token to response
        sync_token_element = ET.Element(_tag("D", "sync-token"))
        sync_token_element.text = sync_token
        multistatus.append(sync_token_element)
    else:
        hreferences = (path,)
    filters = (
        root.findall("./%s" % _tag("C", "filter")) +
        root.findall("./%s" % _tag("CR", "filter")))

    def retrieve_items(collection, hreferences, multistatus):
        """Retrieves all items that are referenced in ``hreferences`` from
           ``collection`` and adds 404 responses for missing and invalid items
           to ``multistatus``."""
        collection_requested = False

        def get_names():
            """Extracts all names from references in ``hreferences`` and adds
               404 responses for invalid references to ``multistatus``.
               If the whole collections is referenced ``collection_requested``
               gets set to ``True``."""
            nonlocal collection_requested
            for hreference in hreferences:
                try:
                    name = name_from_path(hreference, collection)
                except ValueError as e:
                    collection.logger.warning(
                        "Skipping invalid path %r in REPORT request on %r: %s",
                        hreference, path, e)
                    response = _item_response(base_prefix, hreference,
                                              found_item=False)
                    multistatus.append(response)
                    continue
                if name:
                    # Reference is an item
                    yield name
                else:
                    # Reference is a collection
                    collection_requested = True

        for name, item in collection.get_multi2(get_names()):
            if not item:
                uri = "/" + posixpath.join(collection.path, name)
                response = _item_response(base_prefix, uri,
                                          found_item=False)
                multistatus.append(response)
            else:
                yield item, False
        if collection_requested:
            yield from collection.get_all_filtered(filters)

    for item, filters_matched in retrieve_items(collection, hreferences,
                                                multistatus):
        if filters and not filters_matched:
            match = (
                _comp_match if collection.get_meta("tag") == "VCALENDAR"
                else _prop_match)
            try:
                if not all(match(item, filter_[0]) for filter_ in filters
                           if filter_):
                    continue
            except Exception as e:
                raise RuntimeError("Failed to filter item %r from %r: %s" %
                                   (item.href, collection.path, e)) from e

        found_props = []
        not_found_props = []

        for tag in props:
            element = ET.Element(tag)
            if tag == _tag("D", "getetag"):
                element.text = item.etag
                found_props.append(element)
            elif tag == _tag("D", "getcontenttype"):
                name = item.name.lower()
                mimetype = (
                    "text/vcard" if name == "vcard" else "text/calendar")
                element.text = "%s; component=%s" % (mimetype, name)
                found_props.append(element)
            elif tag in (
                    _tag("C", "calendar-data"),
                    _tag("CR", "address-data")):
                element.text = item.serialize()
                found_props.append(element)
            else:
                not_found_props.append(element)

        uri = "/" + posixpath.join(collection.path, item.href)
        multistatus.append(_item_response(
            base_prefix, uri, found_props=found_props,
            not_found_props=not_found_props, found_item=True))

    return client.MULTI_STATUS, multistatus


def _item_response(base_prefix, href, found_props=(), not_found_props=(),
                   found_item=True):
    response = ET.Element(_tag("D", "response"))

    href_tag = ET.Element(_tag("D", "href"))
    href_tag.text = _href(base_prefix, href)
    response.append(href_tag)

    if found_item:
        for code, props in ((200, found_props), (404, not_found_props)):
            if props:
                propstat = ET.Element(_tag("D", "propstat"))
                status = ET.Element(_tag("D", "status"))
                status.text = _response(code)
                prop_tag = ET.Element(_tag("D", "prop"))
                for prop in props:
                    prop_tag.append(prop)
                propstat.append(prop_tag)
                propstat.append(status)
                response.append(propstat)
    else:
        status = ET.Element(_tag("D", "status"))
        status.text = _response(404)
        response.append(status)

    return response