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, 6 insertions, 5 deletions

diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py

index e47799e7f9..9f51212e4e 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -23,6 +23,7 @@ from canonicaljson import encode_canonical_json
 
 from twisted.internet.interfaces import IDelayedCall
 
+import synapse
 from synapse import event_auth
 from synapse.api.constants import (
     EventContentFields,
@@ -881,11 +882,11 @@ class EventCreationHandler:
                 event.sender,
             )
 
-            spam_error = await self.spam_checker.check_event_for_spam(event)
-            if spam_error:
-                if not isinstance(spam_error, str):
-                    spam_error = "Spam is not permitted here"
-                raise SynapseError(403, spam_error, Codes.FORBIDDEN)
+            spam_check = await self.spam_checker.check_event_for_spam(event)
+            if spam_check is not synapse.spam_checker_api.ALLOW:
+                raise SynapseError(
+                    403, "This message had been rejected as probable spam", spam_check
+                )
 
             ev = await self.handle_new_client_event(
                 requester=requester,