Uniformize spam-checker API: github/ts/spam-errors ts/spam-errors

- Some callbacks should return `True` to allow, `False` to deny, while others should return `True` to deny and `False` to allow. With this PR, all callbacks return `ALLOW` to allow or a `Codes` (typically `Codes.FORBIDDEN`) to deny.
- Similarly, some methods returned `True` to allow, `False` to deny, while others returned `True` to deny and `False` to allow. They now all return `ALLOW` to allow or a `Codes` to deny.
- Spam-checker implementations may now return an explicit code, e.g. to differentiate between "User account has been suspended" (which is in practice required by law in some countries, including UK) and "This message looks like spam".

1 files changed, 7 insertions, 3 deletions

diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index be5099b507..aa3be099a5 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -27,6 +27,7 @@ from signedjson.key import decode_verify_key_bytes
 from signedjson.sign import verify_signed_json
 from unpaddedbase64 import decode_base64
 
+import synapse
 from synapse import event_auth
 from synapse.api.constants import EventContentFields, EventTypes, Membership
 from synapse.api.errors import (
@@ -799,11 +800,14 @@ class FederationHandler:
         if self.hs.config.server.block_non_admin_invites:
             raise SynapseError(403, "This server does not accept room invites")
 
-        if not await self.spam_checker.user_may_invite(
+        spam_check = await self.spam_checker.user_may_invite(
             event.sender, event.state_key, event.room_id
-        ):
+        )
+        if spam_check is not synapse.spam_checker_api.ALLOW:
             raise SynapseError(
-                403, "This user is not permitted to send invites to this server/user"
+                403,
+                "This user is not permitted to send invites to this server/user",
+                spam_check,
             )
 
         membership = event.content.get("membership")