Add /user/{user_id}/shared_rooms/ api (#7785)

* Add shared_rooms api

* Add changelog

* Add .

* Wrap response in {"rooms": }

* linting

* Add unstable_features key

* Remove options from isort that aren't part of 5.x

`-y` and `-rc` are now default behaviour and no longer exist.

`dont-skip` is no longer required

https://timothycrosley.github.io/isort/CHANGELOG/#500-penny-july-4-2020

* Update imports to make isort happy

* Add changelog

* Update tox.ini file with correct invocation

* fix linting again for isort

* Vendor prefix unstable API

* Fix to match spec

* import Codes

* import Codes

* Use FORBIDDEN

* Update changelog.d/7785.feature

Co-authored-by: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>

* Implement get_shared_rooms_for_users

* a comma

* trailing whitespace

* Handle the easy feedback

* Switch to using runInteraction

* Add tests

* Feedback

* Seperate unstable endpoint from v2

* Add upgrade node

* a line

* Fix style by adding a blank line at EOF.

* Update synapse/storage/databases/main/user_directory.py

Co-authored-by: Tulir Asokan <tulir@maunium.net>

* Update synapse/storage/databases/main/user_directory.py

Co-authored-by: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>

* Update UPGRADE.rst

Co-authored-by: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>

* Fix UPGRADE/CHANGELOG unstable paths

unstable unstable unstable

Co-authored-by: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>
Co-authored-by: Tulir Asokan <tulir@maunium.net>

Co-authored-by: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>
Co-authored-by: Patrick Cloke <clokep@users.noreply.github.com>
Co-authored-by: Tulir Asokan <tulir@maunium.net>

4 files changed, 117 insertions, 1 deletions

diff --git a/synapse/rest/__init__.py b/synapse/rest/__init__.py
index 46e458e95b..87f927890c 100644
--- a/synapse/rest/__init__.py
+++ b/synapse/rest/__init__.py
@@ -50,6 +50,7 @@ from synapse.rest.client.v2_alpha import (
     room_keys,
     room_upgrade_rest_servlet,
     sendtodevice,
+    shared_rooms,
     sync,
     tags,
     thirdparty,
@@ -125,3 +126,6 @@ class ClientRestResource(JsonResource):
         synapse.rest.admin.register_servlets_for_client_rest_resource(
             hs, client_resource
         )
+
+        # unstable
+        shared_rooms.register_servlets(hs, client_resource)
diff --git a/synapse/rest/client/v2_alpha/shared_rooms.py b/synapse/rest/client/v2_alpha/shared_rooms.py
new file mode 100644
index 0000000000..2492634dac
--- /dev/null
+++ b/synapse/rest/client/v2_alpha/shared_rooms.py
@@ -0,0 +1,68 @@
+# -*- coding: utf-8 -*-
+# Copyright 2020 Half-Shot
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# 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.
+import logging
+
+from synapse.api.errors import Codes, SynapseError
+from synapse.http.servlet import RestServlet
+from synapse.types import UserID
+
+from ._base import client_patterns
+
+logger = logging.getLogger(__name__)
+
+
+class UserSharedRoomsServlet(RestServlet):
+    """
+    GET /uk.half-shot.msc2666/user/shared_rooms/{user_id} HTTP/1.1
+    """
+
+    PATTERNS = client_patterns(
+        "/uk.half-shot.msc2666/user/shared_rooms/(?P<user_id>[^/]*)",
+        releases=(),  # This is an unstable feature
+    )
+
+    def __init__(self, hs):
+        super(UserSharedRoomsServlet, self).__init__()
+        self.auth = hs.get_auth()
+        self.store = hs.get_datastore()
+        self.user_directory_active = hs.config.update_user_directory
+
+    async def on_GET(self, request, user_id):
+
+        if not self.user_directory_active:
+            raise SynapseError(
+                code=400,
+                msg="The user directory is disabled on this server. Cannot determine shared rooms.",
+                errcode=Codes.FORBIDDEN,
+            )
+
+        UserID.from_string(user_id)
+
+        requester = await self.auth.get_user_by_req(request)
+        if user_id == requester.user.to_string():
+            raise SynapseError(
+                code=400,
+                msg="You cannot request a list of shared rooms with yourself",
+                errcode=Codes.FORBIDDEN,
+            )
+        rooms = await self.store.get_shared_rooms_for_users(
+            requester.user.to_string(), user_id
+        )
+
+        return 200, {"joined": list(rooms)}
+
+
+def register_servlets(hs, http_server):
+    UserSharedRoomsServlet(hs).register(http_server)
diff --git a/synapse/rest/client/versions.py b/synapse/rest/client/versions.py
index 0d668df0b6..24ac57f35d 100644
--- a/synapse/rest/client/versions.py
+++ b/synapse/rest/client/versions.py
@@ -60,6 +60,8 @@ class VersionsRestServlet(RestServlet):
                     "org.matrix.e2e_cross_signing": True,
                     # Implements additional endpoints as described in MSC2432
                     "org.matrix.msc2432": True,
+                    # Implements additional endpoints as described in MSC2666
+                    "uk.half-shot.msc2666": True,
                 },
             },
         )
diff --git a/synapse/storage/databases/main/user_directory.py b/synapse/storage/databases/main/user_directory.py
index c977db042e..f2f9a5799a 100644
--- a/synapse/storage/databases/main/user_directory.py
+++ b/synapse/storage/databases/main/user_directory.py
@@ -15,7 +15,7 @@
 
 import logging
 import re
-from typing import Any, Dict, Iterable, Optional, Tuple
+from typing import Any, Dict, Iterable, Optional, Set, Tuple
 
 from synapse.api.constants import EventTypes, JoinRules
 from synapse.storage.database import DatabasePool
@@ -675,6 +675,48 @@ class UserDirectoryStore(UserDirectoryBackgroundUpdateStore):
         users.update(rows)
         return list(users)
 
+    @cached()
+    async def get_shared_rooms_for_users(
+        self, user_id: str, other_user_id: str
+    ) -> Set[str]:
+        """
+        Returns the rooms that a local user shares with another local or remote user.
+
+        Args:
+            user_id: The MXID of a local user
+            other_user_id: The MXID of the other user
+
+        Returns:
+            A set of room ID's that the users share.
+        """
+
+        def _get_shared_rooms_for_users_txn(txn):
+            txn.execute(
+                """
+                SELECT p1.room_id
+                FROM users_in_public_rooms as p1
+                INNER JOIN users_in_public_rooms as p2
+                    ON p1.room_id = p2.room_id
+                    AND p1.user_id = ?
+                    AND p2.user_id = ?
+                UNION
+                SELECT room_id
+                FROM users_who_share_private_rooms
+                WHERE
+                    user_id = ?
+                    AND other_user_id = ?
+                """,
+                (user_id, other_user_id, user_id, other_user_id),
+            )
+            rows = self.db_pool.cursor_to_dict(txn)
+            return rows
+
+        rows = await self.db_pool.runInteraction(
+            "get_shared_rooms_for_users", _get_shared_rooms_for_users_txn
+        )
+
+        return {row["room_id"] for row in rows}
+
     async def get_user_directory_stream_pos(self) -> int:
         return await self.db_pool.simple_select_one_onecol(
             table="user_directory_stream_pos",