synapse/docs/spam_checker.md

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# Handling spam in Synapse
Synapse has support to customize spam checking behavior. It can plug into a
variety of events and affect how they are presented to users on your homeserver.
The spam checking behavior is implemented as a Python class, which must be
able to be imported by the running Synapse.
## Python spam checker class
The Python class is instantiated with two objects:
* Any configuration (see below).
* An instance of `synapse.spam_checker_api.SpamCheckerApi`.
It then implements methods which return a boolean to alter behavior in Synapse.
There's a generic method for checking every event (`check_event_for_spam`), as
well as some specific methods:
* `user_may_invite`
* `user_may_create_room`
* `user_may_create_room_alias`
* `user_may_publish_room`
The details of the each of these methods (as well as their inputs and outputs)
are documented in the `synapse.events.spamcheck.SpamChecker` class.
The `SpamCheckerApi` class provides a way for the custom spam checker class to
call back into the homeserver internals. It currently implements the following
methods:
* `get_state_events_in_room`
### Example
```python
class ExampleSpamChecker:
def __init__(self, config, api):
self.config = config
self.api = api
def check_event_for_spam(self, foo):
return False # allow all events
def user_may_invite(self, inviter_userid, invitee_userid, room_id):
return True # allow all invites
def user_may_create_room(self, userid):
return True # allow all room creations
def user_may_create_room_alias(self, userid, room_alias):
return True # allow all room aliases
def user_may_publish_room(self, userid, room_id):
return True # allow publishing of all rooms
```
## Configuration
Modify the `spam_checker` section of your `homeserver.yaml` in the following
manner:
`module` should point to the fully qualified Python class that implements your
custom logic, e.g. `my_module.ExampleSpamChecker`.
`config` is a dictionary that gets passed to the spam checker class.
### Example
This section might look like:
```yaml
spam_checker:
module: my_module.ExampleSpamChecker
config:
# Enable or disable a specific option in ExampleSpamChecker.
my_custom_option: true
```
## Examples
The [Mjolnir](https://github.com/matrix-org/mjolnir) project is a full fledged
example using the Synapse spam checking API, including a bot for dynamic
configuration.