diff --git a/changelog.d/12808.feature b/changelog.d/12808.feature
new file mode 100644
index 0000000000..561c8b9d34
--- /dev/null
+++ b/changelog.d/12808.feature
@@ -0,0 +1 @@
+Update to `check_event_for_spam`. Deprecate the current callback signature, replace it with a new signature that is both less ambiguous (replacing booleans with explicit allow/block) and more powerful (ability to return explicit error codes).
\ No newline at end of file
diff --git a/docs/modules/spam_checker_callbacks.md b/docs/modules/spam_checker_callbacks.md
index 27c5a0ed5c..71f6f9f0ab 100644
--- a/docs/modules/spam_checker_callbacks.md
+++ b/docs/modules/spam_checker_callbacks.md
@@ -11,22 +11,29 @@ The available spam checker callbacks are:
### `check_event_for_spam`
_First introduced in Synapse v1.37.0_
+_Signature extended to support Allow and Code in Synapse v1.60.0_
+_Boolean and string return value types deprecated in Synapse v1.60.0_
```python
-async def check_event_for_spam(event: "synapse.events.EventBase") -> Union[bool, str]
+async def check_event_for_spam(event: "synapse.module_api.EventBase") -> Union["synapse.module_api.ALLOW", "synapse.module_api.error.Codes", str, bool]
```
-Called when receiving an event from a client or via federation. The callback must return
-either:
-- an error message string, to indicate the event must be rejected because of spam and
- give a rejection reason to forward to clients;
-- the boolean `True`, to indicate that the event is spammy, but not provide further details; or
-- the booelan `False`, to indicate that the event is not considered spammy.
+Called when receiving an event from a client or via federation. The callback must return either:
+ - `synapse.module_api.ALLOW`, to allow the operation. Other callbacks
+ may still decide to reject it.
+ - `synapse.api.Codes` to reject the operation with an error code. In case
+ of doubt, `synapse.api.error.Codes.FORBIDDEN` is a good error code.
+ - (deprecated) a `str` to reject the operation and specify an error message. Note that clients
+ typically will not localize the error message to the user's preferred locale.
+ - (deprecated) on `False`, behave as `ALLOW`. Deprecated as confusing, as some
+ callbacks in expect `True` to allow and others `True` to reject.
+ - (deprecated) on `True`, behave as `synapse.api.error.Codes.FORBIDDEN`. Deprecated as confusing, as
+ some callbacks in expect `True` to allow and others `True` to reject.
If multiple modules implement this callback, they will be considered in order. If a
-callback returns `False`, Synapse falls through to the next one. The value of the first
-callback that does not return `False` will be used. If this happens, Synapse will not call
-any of the subsequent implementations of this callback.
+callback returns `synapse.module_api.ALLOW`, Synapse falls through to the next one. The value of the
+first callback that does not return `synapse.module_api.ALLOW` will be used. If this happens, Synapse
+will not call any of the subsequent implementations of this callback.
### `user_may_join_room`
diff --git a/docs/upgrade.md b/docs/upgrade.md
index 92ca31b2f8..e7eadadb64 100644
--- a/docs/upgrade.md
+++ b/docs/upgrade.md
@@ -177,7 +177,36 @@ has queries that can be used to check a database for this problem in advance.
</details>
+## SpamChecker API's `check_event_for_spam` has a new signature.
+The previous signature has been deprecated.
+
+Whereas `check_event_for_spam` callbacks used to return `Union[str, bool]`, they should now return `Union["synapse.module_api.Allow", "synapse.module_api.errors.Codes"]`.
+
+This is part of an ongoing refactoring of the SpamChecker API to make it less ambiguous and more powerful.
+
+If your module implements `check_event_for_spam` as follows:
+
+```python
+async def check_event_for_spam(event):
+ if ...:
+ # Event is spam
+ return True
+ # Event is not spam
+ return False
+```
+
+you should rewrite it as follows:
+
+```python
+async def check_event_for_spam(event):
+ if ...:
+ # Event is spam, mark it as forbidden (you may use some more precise error
+ # code if it is useful).
+ return synapse.module_api.errors.Codes.FORBIDDEN
+ # Event is not spam, mark it as `ALLOW`.
+ return synapse.module_api.ALLOW
+```
# Upgrading to v1.59.0
diff --git a/synapse/api/errors.py b/synapse/api/errors.py
index 9614be6b4e..6650e826d5 100644
--- a/synapse/api/errors.py
+++ b/synapse/api/errors.py
@@ -270,9 +270,7 @@ class UnrecognizedRequestError(SynapseError):
"""An error indicating we don't understand the request you're trying to make"""
def __init__(
- self,
- msg: str = "Unrecognized request",
- errcode: str = Codes.UNRECOGNIZED,
+ self, msg: str = "Unrecognized request", errcode: str = Codes.UNRECOGNIZED
):
super().__init__(400, msg, errcode)
diff --git a/synapse/events/spamcheck.py b/synapse/events/spamcheck.py
index 61bcbe2abe..7984874e21 100644
--- a/synapse/events/spamcheck.py
+++ b/synapse/events/spamcheck.py
@@ -27,9 +27,10 @@ from typing import (
Union,
)
+from synapse.api.errors import Codes
from synapse.rest.media.v1._base import FileInfo
from synapse.rest.media.v1.media_storage import ReadableFileWrapper
-from synapse.spam_checker_api import RegistrationBehaviour
+from synapse.spam_checker_api import Allow, Decision, RegistrationBehaviour
from synapse.types import RoomAlias, UserProfile
from synapse.util.async_helpers import delay_cancellation, maybe_awaitable
from synapse.util.metrics import Measure
@@ -40,9 +41,19 @@ if TYPE_CHECKING:
logger = logging.getLogger(__name__)
+
CHECK_EVENT_FOR_SPAM_CALLBACK = Callable[
["synapse.events.EventBase"],
- Awaitable[Union[bool, str]],
+ Awaitable[
+ Union[
+ Allow,
+ Codes,
+ # Deprecated
+ bool,
+ # Deprecated
+ str,
+ ]
+ ],
]
SHOULD_DROP_FEDERATED_EVENT_CALLBACK = Callable[
["synapse.events.EventBase"],
@@ -259,7 +270,7 @@ class SpamChecker:
async def check_event_for_spam(
self, event: "synapse.events.EventBase"
- ) -> Union[bool, str]:
+ ) -> Union[Decision, str]:
"""Checks if a given event is considered "spammy" by this server.
If the server considers an event spammy, then it will be rejected if
@@ -270,18 +281,36 @@ class SpamChecker:
event: the event to be checked
Returns:
- True or a string if the event is spammy. If a string is returned it
- will be used as the error message returned to the user.
+ - on `ALLOW`, the event is considered good (non-spammy) and should
+ be let through. Other spamcheck filters may still reject it.
+ - on `Code`, the event is considered spammy and is rejected with a specific
+ error message/code.
+ - on `str`, the event is considered spammy and the string is used as error
+ message. This usage is generally discouraged as it doesn't support
+ internationalization.
"""
for callback in self._check_event_for_spam_callbacks:
with Measure(
self.clock, "{}.{}".format(callback.__module__, callback.__qualname__)
):
- res: Union[bool, str] = await delay_cancellation(callback(event))
- if res:
- return res
-
- return False
+ res: Union[Decision, str, bool] = await delay_cancellation(
+ callback(event)
+ )
+ if res is False or res is Allow.ALLOW:
+ # This spam-checker accepts the event.
+ # Other spam-checkers may reject it, though.
+ continue
+ elif res is True:
+ # This spam-checker rejects the event with deprecated
+ # return value `True`
+ return Codes.FORBIDDEN
+ else:
+ # This spam-checker rejects the event either with a `str`
+ # or with a `Codes`. In either case, we stop here.
+ return res
+
+ # No spam-checker has rejected the event, let it pass.
+ return Allow.ALLOW
async def should_drop_federated_event(
self, event: "synapse.events.EventBase"
diff --git a/synapse/federation/federation_base.py b/synapse/federation/federation_base.py
index 41ac49fdc8..1e866b19d8 100644
--- a/synapse/federation/federation_base.py
+++ b/synapse/federation/federation_base.py
@@ -15,6 +15,7 @@
import logging
from typing import TYPE_CHECKING
+import synapse
from synapse.api.constants import MAX_DEPTH, EventContentFields, EventTypes, Membership
from synapse.api.errors import Codes, SynapseError
from synapse.api.room_versions import EventFormatVersions, RoomVersion
@@ -98,9 +99,9 @@ class FederationBase:
)
return redacted_event
- result = await self.spam_checker.check_event_for_spam(pdu)
+ spam_check = await self.spam_checker.check_event_for_spam(pdu)
- if result:
+ if spam_check is not synapse.spam_checker_api.Allow.ALLOW:
logger.warning("Event contains spam, soft-failing %s", pdu.event_id)
# we redact (to save disk space) as well as soft-failing (to stop
# using the event in prev_events).
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index e566ff1f8e..cb1bc4c06f 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,
@@ -885,11 +886,11 @@ 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.ALLOW:
+ raise SynapseError(
+ 403, "This message had been rejected as probable spam", spam_check
+ )
ev = await self.handle_new_client_event(
requester=requester,
diff --git a/synapse/module_api/__init__.py b/synapse/module_api/__init__.py
index c4f661bb93..95f3b27927 100644
--- a/synapse/module_api/__init__.py
+++ b/synapse/module_api/__init__.py
@@ -35,6 +35,7 @@ from typing_extensions import ParamSpec
from twisted.internet import defer
from twisted.web.resource import Resource
+from synapse import spam_checker_api
from synapse.api.errors import SynapseError
from synapse.events import EventBase
from synapse.events.presence_router import (
@@ -140,6 +141,9 @@ are loaded into Synapse.
PRESENCE_ALL_USERS = PresenceRouter.ALL_USERS
+ALLOW = spam_checker_api.Allow.ALLOW
+# Singleton value used to mark a message as permitted.
+
__all__ = [
"errors",
"make_deferred_yieldable",
@@ -147,6 +151,7 @@ __all__ = [
"respond_with_html",
"run_in_background",
"cached",
+ "Allow",
"UserID",
"DatabasePool",
"LoggingTransaction",
diff --git a/synapse/module_api/errors.py b/synapse/module_api/errors.py
index e58e0e60fe..bedd045d6f 100644
--- a/synapse/module_api/errors.py
+++ b/synapse/module_api/errors.py
@@ -15,6 +15,7 @@
"""Exception types which are exposed as part of the stable module API"""
from synapse.api.errors import (
+ Codes,
InvalidClientCredentialsError,
RedirectException,
SynapseError,
@@ -24,6 +25,7 @@ from synapse.handlers.push_rules import InvalidRuleException
from synapse.storage.push_rule import RuleNotFoundException
__all__ = [
+ "Codes",
"InvalidClientCredentialsError",
"RedirectException",
"SynapseError",
diff --git a/synapse/spam_checker_api/__init__.py b/synapse/spam_checker_api/__init__.py
index 73018f2d00..95132c80b7 100644
--- a/synapse/spam_checker_api/__init__.py
+++ b/synapse/spam_checker_api/__init__.py
@@ -12,13 +12,38 @@
# See the License for the specific language governing permissions and
# limitations under the License.
from enum import Enum
+from typing import Union
+
+from synapse.api.errors import Codes
class RegistrationBehaviour(Enum):
"""
- Enum to define whether a registration request should allowed, denied, or shadow-banned.
+ Enum to define whether a registration request should be allowed, denied, or shadow-banned.
"""
ALLOW = "allow"
SHADOW_BAN = "shadow_ban"
DENY = "deny"
+
+
+# We define the following singleton enum rather than a string to be able to
+# write `Union[Allow, ..., str]` in some of the callbacks for the spam-checker
+# API, where the `str` is required to maintain backwards compatibility with
+# previous versions of the API.
+class Allow(Enum):
+ """
+ Singleton to allow events to pass through in SpamChecker APIs.
+ """
+
+ ALLOW = "allow"
+
+
+Decision = Union[Allow, Codes]
+"""
+Union to define whether a request should be allowed or rejected.
+
+To accept a request, return `ALLOW`.
+
+To reject a request without any specific information, use `Codes.FORBIDDEN`.
+"""
|
