Add support for MSC2697: Dehydrated devices (#8380)

This allows a user to store an offline device on the server and
then restore it at a subsequent login.

synapse/handlers/device.py

@@ -1,7 +1,7 @@
 # -*- coding: utf-8 -*-
 # Copyright 2016 OpenMarket Ltd
 # Copyright 2019 New Vector Ltd
-# Copyright 2019 The Matrix.org Foundation C.I.C.
+# Copyright 2019,2020 The Matrix.org Foundation C.I.C.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -15,7 +15,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 import logging
-from typing import Any, Dict, List, Optional
+from typing import Any, Dict, List, Optional, Tuple
 
 from synapse.api import errors
 from synapse.api.constants import EventTypes
@@ -29,6 +29,7 @@ from synapse.api.errors import (
 from synapse.logging.opentracing import log_kv, set_tag, trace
 from synapse.metrics.background_process_metrics import run_as_background_process
 from synapse.types import (
+    JsonDict,
     StreamToken,
     get_domain_from_id,
     get_verify_key_from_cross_signing_key,
@@ -505,6 +506,85 @@ class DeviceHandler(DeviceWorkerHandler):
             # receive device updates. Mark this in DB.
             await self.store.mark_remote_user_device_list_as_unsubscribed(user_id)
 
+    async def store_dehydrated_device(
+        self,
+        user_id: str,
+        device_data: JsonDict,
+        initial_device_display_name: Optional[str] = None,
+    ) -> str:
+        """Store a dehydrated device for a user.  If the user had a previous
+        dehydrated device, it is removed.
+
+        Args:
+            user_id: the user that we are storing the device for
+            device_data: the dehydrated device information
+            initial_device_display_name: The display name to use for the device
+        Returns:
+            device id of the dehydrated device
+        """
+        device_id = await self.check_device_registered(
+            user_id, None, initial_device_display_name,
+        )
+        old_device_id = await self.store.store_dehydrated_device(
+            user_id, device_id, device_data
+        )
+        if old_device_id is not None:
+            await self.delete_device(user_id, old_device_id)
+        return device_id
+
+    async def get_dehydrated_device(
+        self, user_id: str
+    ) -> Optional[Tuple[str, JsonDict]]:
+        """Retrieve the information for a dehydrated device.
+
+        Args:
+            user_id: the user whose dehydrated device we are looking for
+        Returns:
+            a tuple whose first item is the device ID, and the second item is
+            the dehydrated device information
+        """
+        return await self.store.get_dehydrated_device(user_id)
+
+    async def rehydrate_device(
+        self, user_id: str, access_token: str, device_id: str
+    ) -> dict:
+        """Process a rehydration request from the user.
+
+        Args:
+            user_id: the user who is rehydrating the device
+            access_token: the access token used for the request
+            device_id: the ID of the device that will be rehydrated
+        Returns:
+            a dict containing {"success": True}
+        """
+        success = await self.store.remove_dehydrated_device(user_id, device_id)
+
+        if not success:
+            raise errors.NotFoundError()
+
+        # If the dehydrated device was successfully deleted (the device ID
+        # matched the stored dehydrated device), then modify the access
+        # token to use the dehydrated device's ID and copy the old device
+        # display name to the dehydrated device, and destroy the old device
+        # ID
+        old_device_id = await self.store.set_device_for_access_token(
+            access_token, device_id
+        )
+        old_device = await self.store.get_device(user_id, old_device_id)
+        await self.store.update_device(user_id, device_id, old_device["display_name"])
+        # can't call self.delete_device because that will clobber the
+        # access token so call the storage layer directly
+        await self.store.delete_device(user_id, old_device_id)
+        await self.store.delete_e2e_keys_by_device(
+            user_id=user_id, device_id=old_device_id
+        )
+
+        # tell everyone that the old device is gone and that the dehydrated
+        # device has a new display name
+        await self.notify_device_update(user_id, [old_device_id, device_id])
+
+        return {"success": True}
+
 
 def _update_device_from_client_ips(device, client_ips):
     ip = client_ips.get((device["user_id"], device["device_id"]), {})