Fix dehydrated device REST checks (#14336)

changelog.d/14336.bugfix

+Fix a bug introduced in Synapse 1.70 where clients were unable to PUT new [dehydrated devices](https://github.com/matrix-org/matrix-spec-proposals/pull/2697).

synapse/rest/client/devices.py

@@ -231,7 +231,7 @@ class DehydratedDeviceServlet(RestServlet):
       }
     }
 
-    PUT /org.matrix.msc2697/dehydrated_device
+    PUT /org.matrix.msc2697.v2/dehydrated_device
     Content-Type: application/json
 
     {
@@ -271,7 +271,6 @@ class DehydratedDeviceServlet(RestServlet):
             raise errors.NotFoundError("No dehydrated device available")
 
     class PutBody(RequestBodyModel):
-        device_id: StrictStr
         device_data: DehydratedDeviceDataModel
         initial_device_display_name: Optional[StrictStr]
 
@@ -281,7 +280,7 @@ class DehydratedDeviceServlet(RestServlet):
 
         device_id = await self.device_handler.store_dehydrated_device(
             requester.user.to_string(),
-            submission.device_data,
+            submission.device_data.dict(),
             submission.initial_device_display_name,
         )
         return 200, {"device_id": device_id}

tests/rest/client/test_devices.py

@@ -200,3 +200,37 @@ class DevicesTestCase(unittest.HomeserverTestCase):
         self.reactor.advance(43200)
         self.get_success(self.handler.get_device(user_id, "abc"))
         self.get_failure(self.handler.get_device(user_id, "def"), NotFoundError)
+
+
+class DehydratedDeviceTestCase(unittest.HomeserverTestCase):
+    servlets = [
+        admin.register_servlets_for_client_rest_resource,
+        login.register_servlets,
+        register.register_servlets,
+        devices.register_servlets,
+    ]
+
+    def test_PUT(self) -> None:
+        """Sanity-check that we can PUT a dehydrated device.
+
+        Detects https://github.com/matrix-org/synapse/issues/14334.
+        """
+        alice = self.register_user("alice", "correcthorse")
+        token = self.login(alice, "correcthorse")
+
+        # Have alice update their device list
+        channel = self.make_request(
+            "PUT",
+            "_matrix/client/unstable/org.matrix.msc2697.v2/dehydrated_device",
+            {
+                "device_data": {
+                    "algorithm": "org.matrix.msc2697.v1.dehydration.v1.olm",
+                    "account": "dehydrated_device",
+                }
+            },
+            access_token=token,
+            shorthand=False,
+        )
+        self.assertEqual(channel.code, HTTPStatus.OK, channel.json_body)
+        device_id = channel.json_body.get("device_id")
+        self.assertIsInstance(device_id, str)