synapse-old/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.module_api.ModuleApi`.
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`
* `check_username_for_spam`
* `check_registration_for_spam`
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 `ModuleApi` class provides a way for the custom spam checker class to
call back into the homeserver internals.
### Example
```python
from synapse.spam_checker_api import RegistrationBehaviour
class ExampleSpamChecker:
def __init__(self, config, api):
self.config = config
self.api = api
async def check_event_for_spam(self, foo):
return False # allow all events
async def user_may_invite(self, inviter_userid, invitee_userid, room_id):
return True # allow all invites
async def user_may_create_room(self, userid):
return True # allow all room creations
async def user_may_create_room_alias(self, userid, room_alias):
return True # allow all room aliases
async def user_may_publish_room(self, userid, room_id):
return True # allow publishing of all rooms
async def check_username_for_spam(self, user_profile):
return False # allow all usernames
async def check_registration_for_spam(self, email_threepid, username, request_info):
return RegistrationBehaviour.ALLOW # allow all registrations
```
## Configuration
Modify the `spam_checker` section of your `homeserver.yaml` in the following
manner:
Create a list entry with the keys `module` and `config`.
* `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
```
More spam checkers can be added in tandem by appending more items to the list. An
action is blocked when at least one of the configured spam checkers flags it.
## 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.