From 39be5bc550f2e882b4754c7d98c906d9bde8b649 Mon Sep 17 00:00:00 2001
From: reivilibre <oliverw@matrix.org>
Date: Wed, 27 Jul 2022 10:37:50 +0000
Subject: [PATCH] Make minor clarifications to the error messages given when we
 fail to join a room via any server. (#13160)

---
 changelog.d/13160.misc                  | 1 +
 synapse/federation/federation_client.py | 8 +++++++-
 synapse/handlers/room_member.py         | 6 +++++-
 tests/rest/admin/test_room.py           | 5 ++++-
 4 files changed, 17 insertions(+), 3 deletions(-)
 create mode 100644 changelog.d/13160.misc

diff --git a/changelog.d/13160.misc b/changelog.d/13160.misc
new file mode 100644
index 0000000000..36ff50c2a6
--- /dev/null
+++ b/changelog.d/13160.misc
@@ -0,0 +1 @@
+Make minor clarifications to the error messages given when we fail to join a room via any server.
\ No newline at end of file
diff --git a/synapse/federation/federation_client.py b/synapse/federation/federation_client.py
index 02276ed995..6a8d76529b 100644
--- a/synapse/federation/federation_client.py
+++ b/synapse/federation/federation_client.py
@@ -725,6 +725,12 @@ class FederationClient(FederationBase):
         if failover_errcodes is None:
             failover_errcodes = ()
 
+        if not destinations:
+            # Give a bit of a clearer message if no servers were specified at all.
+            raise SynapseError(
+                502, f"Failed to {description} via any server: No servers specified."
+            )
+
         for destination in destinations:
             if destination == self.server_name:
                 continue
@@ -774,7 +780,7 @@ class FederationClient(FederationBase):
                     "Failed to %s via %s", description, destination, exc_info=True
                 )
 
-        raise SynapseError(502, "Failed to %s via any server" % (description,))
+        raise SynapseError(502, f"Failed to {description} via any server")
 
     async def make_membership_event(
         self,
diff --git a/synapse/handlers/room_member.py b/synapse/handlers/room_member.py
index 30b4cb23df..520c52e013 100644
--- a/synapse/handlers/room_member.py
+++ b/synapse/handlers/room_member.py
@@ -1679,7 +1679,11 @@ class RoomMemberMasterHandler(RoomMemberHandler):
         ]
 
         if len(remote_room_hosts) == 0:
-            raise SynapseError(404, "No known servers")
+            raise SynapseError(
+                404,
+                "Can't join remote room because no servers "
+                "that are in the room have been provided.",
+            )
 
         check_complexity = self.hs.config.server.limit_remote_rooms.enabled
         if (
diff --git a/tests/rest/admin/test_room.py b/tests/rest/admin/test_room.py
index 2526136ff8..623883b53c 100644
--- a/tests/rest/admin/test_room.py
+++ b/tests/rest/admin/test_room.py
@@ -1873,7 +1873,10 @@ class JoinAliasRoomTestCase(unittest.HomeserverTestCase):
         )
 
         self.assertEqual(HTTPStatus.NOT_FOUND, channel.code, msg=channel.json_body)
-        self.assertEqual("No known servers", channel.json_body["error"])
+        self.assertEqual(
+            "Can't join remote room because no servers that are in the room have been provided.",
+            channel.json_body["error"],
+        )
 
     def test_room_is_not_valid(self) -> None:
         """