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-rw-r--r--synapse/api/auth.py241
-rw-r--r--synapse/api/constants.py20
-rw-r--r--synapse/api/errors.py154
-rw-r--r--synapse/api/filtering.py33
-rw-r--r--synapse/api/ratelimiting.py2
-rw-r--r--synapse/api/urls.py2
6 files changed, 320 insertions, 132 deletions
diff --git a/synapse/api/auth.py b/synapse/api/auth.py
index 06fa38366d..34382e4e3c 100644
--- a/synapse/api/auth.py
+++ b/synapse/api/auth.py
@@ -18,14 +18,17 @@ import logging
 from six import itervalues
 
 import pymacaroons
+from netaddr import IPAddress
+
 from twisted.internet import defer
 
 import synapse.types
 from synapse import event_auth
-from synapse.api.constants import EventTypes, Membership, JoinRules
-from synapse.api.errors import AuthError, Codes
+from synapse.api.constants import EventTypes, JoinRules, Membership
+from synapse.api.errors import AuthError, Codes, ResourceLimitError
+from synapse.config.server import is_threepid_reserved
 from synapse.types import UserID
-from synapse.util.caches import register_cache, CACHE_SIZE_FACTOR
+from synapse.util.caches import CACHE_SIZE_FACTOR, register_cache
 from synapse.util.caches.lrucache import LruCache
 from synapse.util.metrics import Measure
 
@@ -63,8 +66,9 @@ class Auth(object):
 
     @defer.inlineCallbacks
     def check_from_context(self, event, context, do_sig_check=True):
+        prev_state_ids = yield context.get_prev_state_ids(self.store)
         auth_events_ids = yield self.compute_auth_events(
-            event, context.prev_state_ids, for_verification=True,
+            event, prev_state_ids, for_verification=True,
         )
         auth_events = yield self.store.get_events(auth_events_ids)
         auth_events = {
@@ -191,7 +195,7 @@ class Auth(object):
                     synapse.types.create_requester(user_id, app_service=app_service)
                 )
 
-            access_token = get_access_token_from_request(
+            access_token = self.get_access_token_from_request(
                 request, self.TOKEN_NOT_FOUND_HTTP_STATUS
             )
 
@@ -208,9 +212,9 @@ class Auth(object):
             user_agent = request.requestHeaders.getRawHeaders(
                 b"User-Agent",
                 default=[b""]
-            )[0]
+            )[0].decode('ascii', 'surrogateescape')
             if user and access_token and ip_addr:
-                self.store.insert_client_ip(
+                yield self.store.insert_client_ip(
                     user_id=user.to_string(),
                     access_token=access_token,
                     ip=ip_addr,
@@ -237,17 +241,22 @@ class Auth(object):
     @defer.inlineCallbacks
     def _get_appservice_user_id(self, request):
         app_service = self.store.get_app_service_by_token(
-            get_access_token_from_request(
+            self.get_access_token_from_request(
                 request, self.TOKEN_NOT_FOUND_HTTP_STATUS
             )
         )
         if app_service is None:
             defer.returnValue((None, None))
 
-        if "user_id" not in request.args:
+        if app_service.ip_range_whitelist:
+            ip_address = IPAddress(self.hs.get_ip_from_request(request))
+            if ip_address not in app_service.ip_range_whitelist:
+                defer.returnValue((None, None))
+
+        if b"user_id" not in request.args:
             defer.returnValue((app_service.sender, app_service))
 
-        user_id = request.args["user_id"][0]
+        user_id = request.args[b"user_id"][0].decode('utf8')
         if app_service.sender == user_id:
             defer.returnValue((app_service.sender, app_service))
 
@@ -488,7 +497,7 @@ class Auth(object):
     def _look_up_user_by_access_token(self, token):
         ret = yield self.store.get_user_by_access_token(token)
         if not ret:
-            logger.warn("Unrecognised access token - not in store: %s" % (token,))
+            logger.warn("Unrecognised access token - not in store.")
             raise AuthError(
                 self.TOKEN_NOT_FOUND_HTTP_STATUS, "Unrecognised access token.",
                 errcode=Codes.UNKNOWN_TOKEN
@@ -506,12 +515,12 @@ class Auth(object):
 
     def get_appservice_by_req(self, request):
         try:
-            token = get_access_token_from_request(
+            token = self.get_access_token_from_request(
                 request, self.TOKEN_NOT_FOUND_HTTP_STATUS
             )
             service = self.store.get_app_service_by_token(token)
             if not service:
-                logger.warn("Unrecognised appservice access token: %s" % (token,))
+                logger.warn("Unrecognised appservice access token.")
                 raise AuthError(
                     self.TOKEN_NOT_FOUND_HTTP_STATUS,
                     "Unrecognised access token.",
@@ -537,7 +546,8 @@ class Auth(object):
 
     @defer.inlineCallbacks
     def add_auth_events(self, builder, context):
-        auth_ids = yield self.compute_auth_events(builder, context.prev_state_ids)
+        prev_state_ids = yield context.get_prev_state_ids(self.store)
+        auth_ids = yield self.compute_auth_events(builder, prev_state_ids)
 
         auth_events_entries = yield self.store.add_event_hashes(
             auth_ids
@@ -655,7 +665,7 @@ class Auth(object):
             auth_events[(EventTypes.PowerLevels, "")] = power_level_event
 
         send_level = event_auth.get_send_level(
-            EventTypes.Aliases, "", auth_events
+            EventTypes.Aliases, "", power_level_event,
         )
         user_level = event_auth.get_user_power_level(user_id, auth_events)
 
@@ -666,67 +676,156 @@ class Auth(object):
                 " edit its room list entry"
             )
 
+    @staticmethod
+    def has_access_token(request):
+        """Checks if the request has an access_token.
 
-def has_access_token(request):
-    """Checks if the request has an access_token.
+        Returns:
+            bool: False if no access_token was given, True otherwise.
+        """
+        query_params = request.args.get(b"access_token")
+        auth_headers = request.requestHeaders.getRawHeaders(b"Authorization")
+        return bool(query_params) or bool(auth_headers)
 
-    Returns:
-        bool: False if no access_token was given, True otherwise.
-    """
-    query_params = request.args.get("access_token")
-    auth_headers = request.requestHeaders.getRawHeaders(b"Authorization")
-    return bool(query_params) or bool(auth_headers)
-
-
-def get_access_token_from_request(request, token_not_found_http_status=401):
-    """Extracts the access_token from the request.
-
-    Args:
-        request: The http request.
-        token_not_found_http_status(int): The HTTP status code to set in the
-            AuthError if the token isn't found. This is used in some of the
-            legacy APIs to change the status code to 403 from the default of
-            401 since some of the old clients depended on auth errors returning
-            403.
-    Returns:
-        str: The access_token
-    Raises:
-        AuthError: If there isn't an access_token in the request.
-    """
+    @staticmethod
+    def get_access_token_from_request(request, token_not_found_http_status=401):
+        """Extracts the access_token from the request.
 
-    auth_headers = request.requestHeaders.getRawHeaders(b"Authorization")
-    query_params = request.args.get(b"access_token")
-    if auth_headers:
-        # Try the get the access_token from a "Authorization: Bearer"
-        # header
-        if query_params is not None:
-            raise AuthError(
-                token_not_found_http_status,
-                "Mixing Authorization headers and access_token query parameters.",
-                errcode=Codes.MISSING_TOKEN,
-            )
-        if len(auth_headers) > 1:
-            raise AuthError(
-                token_not_found_http_status,
-                "Too many Authorization headers.",
-                errcode=Codes.MISSING_TOKEN,
-            )
-        parts = auth_headers[0].split(" ")
-        if parts[0] == "Bearer" and len(parts) == 2:
-            return parts[1]
+        Args:
+            request: The http request.
+            token_not_found_http_status(int): The HTTP status code to set in the
+                AuthError if the token isn't found. This is used in some of the
+                legacy APIs to change the status code to 403 from the default of
+                401 since some of the old clients depended on auth errors returning
+                403.
+        Returns:
+            unicode: The access_token
+        Raises:
+            AuthError: If there isn't an access_token in the request.
+        """
+
+        auth_headers = request.requestHeaders.getRawHeaders(b"Authorization")
+        query_params = request.args.get(b"access_token")
+        if auth_headers:
+            # Try the get the access_token from a "Authorization: Bearer"
+            # header
+            if query_params is not None:
+                raise AuthError(
+                    token_not_found_http_status,
+                    "Mixing Authorization headers and access_token query parameters.",
+                    errcode=Codes.MISSING_TOKEN,
+                )
+            if len(auth_headers) > 1:
+                raise AuthError(
+                    token_not_found_http_status,
+                    "Too many Authorization headers.",
+                    errcode=Codes.MISSING_TOKEN,
+                )
+            parts = auth_headers[0].split(b" ")
+            if parts[0] == b"Bearer" and len(parts) == 2:
+                return parts[1].decode('ascii')
+            else:
+                raise AuthError(
+                    token_not_found_http_status,
+                    "Invalid Authorization header.",
+                    errcode=Codes.MISSING_TOKEN,
+                )
         else:
-            raise AuthError(
-                token_not_found_http_status,
-                "Invalid Authorization header.",
-                errcode=Codes.MISSING_TOKEN,
+            # Try to get the access_token from the query params.
+            if not query_params:
+                raise AuthError(
+                    token_not_found_http_status,
+                    "Missing access token.",
+                    errcode=Codes.MISSING_TOKEN
+                )
+
+            return query_params[0].decode('ascii')
+
+    @defer.inlineCallbacks
+    def check_in_room_or_world_readable(self, room_id, user_id):
+        """Checks that the user is or was in the room or the room is world
+        readable. If it isn't then an exception is raised.
+
+        Returns:
+            Deferred[tuple[str, str|None]]: Resolves to the current membership of
+            the user in the room and the membership event ID of the user. If
+            the user is not in the room and never has been, then
+            `(Membership.JOIN, None)` is returned.
+        """
+
+        try:
+            # check_user_was_in_room will return the most recent membership
+            # event for the user if:
+            #  * The user is a non-guest user, and was ever in the room
+            #  * The user is a guest user, and has joined the room
+            # else it will throw.
+            member_event = yield self.check_user_was_in_room(room_id, user_id)
+            defer.returnValue((member_event.membership, member_event.event_id))
+        except AuthError:
+            visibility = yield self.state.get_current_state(
+                room_id, EventTypes.RoomHistoryVisibility, ""
             )
-    else:
-        # Try to get the access_token from the query params.
-        if not query_params:
+            if (
+                visibility and
+                visibility.content["history_visibility"] == "world_readable"
+            ):
+                defer.returnValue((Membership.JOIN, None))
+                return
             raise AuthError(
-                token_not_found_http_status,
-                "Missing access token.",
-                errcode=Codes.MISSING_TOKEN
+                403, "Guest access not allowed", errcode=Codes.GUEST_ACCESS_FORBIDDEN
+            )
+
+    @defer.inlineCallbacks
+    def check_auth_blocking(self, user_id=None, threepid=None):
+        """Checks if the user should be rejected for some external reason,
+        such as monthly active user limiting or global disable flag
+
+        Args:
+            user_id(str|None): If present, checks for presence against existing
+            MAU cohort
+
+            threepid(dict|None): If present, checks for presence against configured
+            reserved threepid. Used in cases where the user is trying register
+            with a MAU blocked server, normally they would be rejected but their
+            threepid is on the reserved list. user_id and
+            threepid should never be set at the same time.
+        """
+
+        # Never fail an auth check for the server notices users
+        # This can be a problem where event creation is prohibited due to blocking
+        if user_id == self.hs.config.server_notices_mxid:
+            return
+
+        if self.hs.config.hs_disabled:
+            raise ResourceLimitError(
+                403, self.hs.config.hs_disabled_message,
+                errcode=Codes.RESOURCE_LIMIT_EXCEEDED,
+                admin_contact=self.hs.config.admin_contact,
+                limit_type=self.hs.config.hs_disabled_limit_type
             )
+        if self.hs.config.limit_usage_by_mau is True:
+            assert not (user_id and threepid)
 
-        return query_params[0]
+            # If the user is already part of the MAU cohort or a trial user
+            if user_id:
+                timestamp = yield self.store.user_last_seen_monthly_active(user_id)
+                if timestamp:
+                    return
+
+                is_trial = yield self.store.is_trial_user(user_id)
+                if is_trial:
+                    return
+            elif threepid:
+                # If the user does not exist yet, but is signing up with a
+                # reserved threepid then pass auth check
+                if is_threepid_reserved(self.hs.config, threepid):
+                    return
+            # Else if there is no room in the MAU bucket, bail
+            current_mau = yield self.store.get_monthly_active_count()
+            if current_mau >= self.hs.config.max_mau_value:
+                raise ResourceLimitError(
+                    403, "Monthly Active User Limit Exceeded",
+                    admin_contact=self.hs.config.admin_contact,
+                    errcode=Codes.RESOURCE_LIMIT_EXCEEDED,
+                    limit_type="monthly_active_user"
+                )
diff --git a/synapse/api/constants.py b/synapse/api/constants.py
index 5baba43966..c2630c4c64 100644
--- a/synapse/api/constants.py
+++ b/synapse/api/constants.py
@@ -1,6 +1,7 @@
 # -*- coding: utf-8 -*-
 # Copyright 2014-2016 OpenMarket Ltd
 # Copyright 2017 Vector Creations Ltd
+# Copyright 2018 New Vector Ltd.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -76,6 +77,9 @@ class EventTypes(object):
     Topic = "m.room.topic"
     Name = "m.room.name"
 
+    ServerACL = "m.room.server_acl"
+    Pinned = "m.room.pinned_events"
+
 
 class RejectedReason(object):
     AUTH_ERROR = "auth_error"
@@ -92,3 +96,19 @@ class RoomCreationPreset(object):
 class ThirdPartyEntityKind(object):
     USER = "user"
     LOCATION = "location"
+
+
+class RoomVersions(object):
+    V1 = "1"
+    VDH_TEST = "vdh-test-version"
+
+
+# the version we will give rooms which are created on this server
+DEFAULT_ROOM_VERSION = RoomVersions.V1
+
+# vdh-test-version is a placeholder to get room versioning support working and tested
+# until we have a working v2.
+KNOWN_ROOM_VERSIONS = {RoomVersions.V1, RoomVersions.VDH_TEST}
+
+ServerNoticeMsgType = "m.server_notice"
+ServerNoticeLimitReached = "m.server_notice.usage_limit_reached"
diff --git a/synapse/api/errors.py b/synapse/api/errors.py
index e6ad3768f0..2e7f98404d 100644
--- a/synapse/api/errors.py
+++ b/synapse/api/errors.py
@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
 # Copyright 2014-2016 OpenMarket Ltd
+# Copyright 2018 New Vector Ltd.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -17,10 +18,11 @@
 
 import logging
 
-import simplejson as json
 from six import iteritems
 from six.moves import http_client
 
+from canonicaljson import json
+
 logger = logging.getLogger(__name__)
 
 
@@ -54,6 +56,9 @@ class Codes(object):
     SERVER_NOT_TRUSTED = "M_SERVER_NOT_TRUSTED"
     CONSENT_NOT_GIVEN = "M_CONSENT_NOT_GIVEN"
     CANNOT_LEAVE_SERVER_NOTICE_ROOM = "M_CANNOT_LEAVE_SERVER_NOTICE_ROOM"
+    RESOURCE_LIMIT_EXCEEDED = "M_RESOURCE_LIMIT_EXCEEDED"
+    UNSUPPORTED_ROOM_VERSION = "M_UNSUPPORTED_ROOM_VERSION"
+    INCOMPATIBLE_ROOM_VERSION = "M_INCOMPATIBLE_ROOM_VERSION"
 
 
 class CodeMessageException(RuntimeError):
@@ -68,20 +73,6 @@ class CodeMessageException(RuntimeError):
         self.code = code
         self.msg = msg
 
-    def error_dict(self):
-        return cs_error(self.msg)
-
-
-class MatrixCodeMessageException(CodeMessageException):
-    """An error from a general matrix endpoint, eg. from a proxied Matrix API call.
-
-    Attributes:
-        errcode (str): Matrix error code e.g 'M_FORBIDDEN'
-    """
-    def __init__(self, code, msg, errcode=Codes.UNKNOWN):
-        super(MatrixCodeMessageException, self).__init__(code, msg)
-        self.errcode = errcode
-
 
 class SynapseError(CodeMessageException):
     """A base exception type for matrix errors which have an errcode and error
@@ -107,38 +98,28 @@ class SynapseError(CodeMessageException):
             self.errcode,
         )
 
-    @classmethod
-    def from_http_response_exception(cls, err):
-        """Make a SynapseError based on an HTTPResponseException
-
-        This is useful when a proxied request has failed, and we need to
-        decide how to map the failure onto a matrix error to send back to the
-        client.
 
-        An attempt is made to parse the body of the http response as a matrix
-        error. If that succeeds, the errcode and error message from the body
-        are used as the errcode and error message in the new synapse error.
-
-        Otherwise, the errcode is set to M_UNKNOWN, and the error message is
-        set to the reason code from the HTTP response.
-
-        Args:
-            err (HttpResponseException):
+class ProxiedRequestError(SynapseError):
+    """An error from a general matrix endpoint, eg. from a proxied Matrix API call.
 
-        Returns:
-            SynapseError:
-        """
-        # try to parse the body as json, to get better errcode/msg, but
-        # default to M_UNKNOWN with the HTTP status as the error text
-        try:
-            j = json.loads(err.response)
-        except ValueError:
-            j = {}
-        errcode = j.get('errcode', Codes.UNKNOWN)
-        errmsg = j.get('error', err.msg)
+    Attributes:
+        errcode (str): Matrix error code e.g 'M_FORBIDDEN'
+    """
+    def __init__(self, code, msg, errcode=Codes.UNKNOWN, additional_fields=None):
+        super(ProxiedRequestError, self).__init__(
+            code, msg, errcode
+        )
+        if additional_fields is None:
+            self._additional_fields = {}
+        else:
+            self._additional_fields = dict(additional_fields)
 
-        res = SynapseError(err.code, errmsg, errcode)
-        return res
+    def error_dict(self):
+        return cs_error(
+            self.msg,
+            self.errcode,
+            **self._additional_fields
+        )
 
 
 class ConsentNotGivenError(SynapseError):
@@ -250,6 +231,30 @@ class AuthError(SynapseError):
         super(AuthError, self).__init__(*args, **kwargs)
 
 
+class ResourceLimitError(SynapseError):
+    """
+    Any error raised when there is a problem with resource usage.
+    For instance, the monthly active user limit for the server has been exceeded
+    """
+    def __init__(
+        self, code, msg,
+        errcode=Codes.RESOURCE_LIMIT_EXCEEDED,
+        admin_contact=None,
+        limit_type=None,
+    ):
+        self.admin_contact = admin_contact
+        self.limit_type = limit_type
+        super(ResourceLimitError, self).__init__(code, msg, errcode=errcode)
+
+    def error_dict(self):
+        return cs_error(
+            self.msg,
+            self.errcode,
+            admin_contact=self.admin_contact,
+            limit_type=self.limit_type
+        )
+
+
 class EventSizeError(SynapseError):
     """An error raised when an event is too big."""
 
@@ -307,12 +312,25 @@ class LimitExceededError(SynapseError):
         )
 
 
-def cs_exception(exception):
-    if isinstance(exception, CodeMessageException):
-        return exception.error_dict()
-    else:
-        logger.error("Unknown exception type: %s", type(exception))
-        return {}
+class IncompatibleRoomVersionError(SynapseError):
+    """A server is trying to join a room whose version it does not support."""
+
+    def __init__(self, room_version):
+        super(IncompatibleRoomVersionError, self).__init__(
+            code=400,
+            msg="Your homeserver does not support the features required to "
+                "join this room",
+            errcode=Codes.INCOMPATIBLE_ROOM_VERSION,
+        )
+
+        self._room_version = room_version
+
+    def error_dict(self):
+        return cs_error(
+            self.msg,
+            self.errcode,
+            room_version=self._room_version,
+        )
 
 
 def cs_error(msg, code=Codes.UNKNOWN, **kwargs):
@@ -371,7 +389,7 @@ class HttpResponseException(CodeMessageException):
     Represents an HTTP-level failure of an outbound request
 
     Attributes:
-        response (str): body of response
+        response (bytes): body of response
     """
     def __init__(self, code, msg, response):
         """
@@ -379,7 +397,39 @@ class HttpResponseException(CodeMessageException):
         Args:
             code (int): HTTP status code
             msg (str): reason phrase from HTTP response status line
-            response (str): body of response
+            response (bytes): body of response
         """
         super(HttpResponseException, self).__init__(code, msg)
         self.response = response
+
+    def to_synapse_error(self):
+        """Make a SynapseError based on an HTTPResponseException
+
+        This is useful when a proxied request has failed, and we need to
+        decide how to map the failure onto a matrix error to send back to the
+        client.
+
+        An attempt is made to parse the body of the http response as a matrix
+        error. If that succeeds, the errcode and error message from the body
+        are used as the errcode and error message in the new synapse error.
+
+        Otherwise, the errcode is set to M_UNKNOWN, and the error message is
+        set to the reason code from the HTTP response.
+
+        Returns:
+            SynapseError:
+        """
+        # try to parse the body as json, to get better errcode/msg, but
+        # default to M_UNKNOWN with the HTTP status as the error text
+        try:
+            j = json.loads(self.response)
+        except ValueError:
+            j = {}
+
+        if not isinstance(j, dict):
+            j = {}
+
+        errcode = j.pop('errcode', Codes.UNKNOWN)
+        errmsg = j.pop('error', self.msg)
+
+        return ProxiedRequestError(self.code, errmsg, errcode, j)
diff --git a/synapse/api/filtering.py b/synapse/api/filtering.py
index dbc0e7e445..186831e118 100644
--- a/synapse/api/filtering.py
+++ b/synapse/api/filtering.py
@@ -12,15 +12,16 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-from synapse.api.errors import SynapseError
-from synapse.storage.presence import UserPresenceState
-from synapse.types import UserID, RoomID
-from twisted.internet import defer
-
-import simplejson as json
 import jsonschema
+from canonicaljson import json
 from jsonschema import FormatChecker
 
+from twisted.internet import defer
+
+from synapse.api.errors import SynapseError
+from synapse.storage.presence import UserPresenceState
+from synapse.types import RoomID, UserID
+
 FILTER_SCHEMA = {
     "additionalProperties": False,
     "type": "object",
@@ -112,7 +113,13 @@ ROOM_EVENT_FILTER_SCHEMA = {
         },
         "contains_url": {
             "type": "boolean"
-        }
+        },
+        "lazy_load_members": {
+            "type": "boolean"
+        },
+        "include_redundant_members": {
+            "type": "boolean"
+        },
     }
 }
 
@@ -260,6 +267,12 @@ class FilterCollection(object):
     def ephemeral_limit(self):
         return self._room_ephemeral_filter.limit()
 
+    def lazy_load_members(self):
+        return self._room_state_filter.lazy_load_members()
+
+    def include_redundant_members(self):
+        return self._room_state_filter.include_redundant_members()
+
     def filter_presence(self, events):
         return self._presence_filter.filter(events)
 
@@ -416,6 +429,12 @@ class Filter(object):
     def limit(self):
         return self.filter_json.get("limit", 10)
 
+    def lazy_load_members(self):
+        return self.filter_json.get("lazy_load_members", False)
+
+    def include_redundant_members(self):
+        return self.filter_json.get("include_redundant_members", False)
+
 
 def _matches_wildcard(actual_value, filter_value):
     if filter_value.endswith("*"):
diff --git a/synapse/api/ratelimiting.py b/synapse/api/ratelimiting.py
index 06cc8d90b8..3bb5b3da37 100644
--- a/synapse/api/ratelimiting.py
+++ b/synapse/api/ratelimiting.py
@@ -72,7 +72,7 @@ class Ratelimiter(object):
         return allowed, time_allowed
 
     def prune_message_counts(self, time_now_s):
-        for user_id in self.message_counts.keys():
+        for user_id in list(self.message_counts.keys()):
             message_count, time_start, msg_rate_hz = (
                 self.message_counts[user_id]
             )
diff --git a/synapse/api/urls.py b/synapse/api/urls.py
index bb46b5da8a..71347912f1 100644
--- a/synapse/api/urls.py
+++ b/synapse/api/urls.py
@@ -15,8 +15,8 @@
 # limitations under the License.
 
 """Contains the URL paths to prefix various aspects of the server with. """
-from hashlib import sha256
 import hmac
+from hashlib import sha256
 
 from six.moves.urllib.parse import urlencode