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Modules

Synapse supports extending its functionality by configuring external modules.

Using modules

To use a module on Synapse, add it to the modules section of the configuration file:

modules:
  - module: my_super_module.MySuperClass
    config:
      do_thing: true
  - module: my_other_super_module.SomeClass
    config: {}

Each module is defined by a path to a Python class as well as a configuration. This information for a given module should be available in the module's own documentation.

Note: When using third-party modules, you effectively allow someone else to run custom code on your Synapse homeserver. Server admins are encouraged to verify the provenance of the modules they use on their homeserver and make sure the modules aren't running malicious code on their instance.

Also note that we are currently in the process of migrating module interfaces to this system. While some interfaces might be compatible with it, others still require configuring modules in another part of Synapse's configuration file. Currently, only the spam checker interface is compatible with this new system.

Writing a module

A module is a Python class that uses Synapse's module API to interact with the homeserver. It can register callbacks that Synapse will call on specific operations, as well as web resources to attach to Synapse's web server.

When instantiated, a module is given its parsed configuration as well as an instance of the synapse.module_api.ModuleApi class. The configuration is a dictionary, and is either the output of the module's parse_config static method (see below), or the configuration associated with the module in Synapse's configuration file.

See the documentation for the ModuleApi class here.

Handling the module's configuration

A module can implement the following static method:

@staticmethod
def parse_config(config: dict) -> dict

This method is given a dictionary resulting from parsing the YAML configuration for the module. It may modify it (for example by parsing durations expressed as strings (e.g. "5d") into milliseconds, etc.), and return the modified dictionary. It may also verify that the configuration is correct, and raise an instance of synapse.module_api.errors.ConfigError if not.

Registering a web resource

Modules can register web resources onto Synapse's web server using the following module API method:

def ModuleApi.register_web_resource(path: str, resource: IResource)

The path is the full absolute path to register the resource at. For example, if you register a resource for the path /_synapse/client/my_super_module/say_hello, Synapse will serve it at http(s)://[HS_URL]/_synapse/client/my_super_module/say_hello. Note that Synapse does not allow registering resources for several sub-paths in the /_matrix namespace (such as anything under /_matrix/client for example). It is strongly recommended that modules register their web resources under the /_synapse/client namespace.

The provided resource is a Python class that implements Twisted's IResource interface (such as Resource).

Only one resource can be registered for a given path. If several modules attempt to register a resource for the same path, the module that appears first in Synapse's configuration file takes priority.

Modules must register their web resources in their __init__ method.

Registering a callback

Modules can use Synapse's module API to register callbacks. Callbacks are functions that Synapse will call when performing specific actions. Callbacks must be asynchronous, and are split in categories. A single module may implement callbacks from multiple categories, and is under no obligation to implement all callbacks from the categories it registers callbacks for.

Spam checker callbacks

To register one of the callbacks described in this section, a module needs to use the module API's register_spam_checker_callbacks method. The callback functions are passed to register_spam_checker_callbacks as keyword arguments, with the callback name as the argument name and the function as its value. This is demonstrated in the example below.

The available spam checker callbacks are:

def check_event_for_spam(event: "synapse.events.EventBase") -> Union[bool, str]

Called when receiving an event from a client or via federation. The module can return either a bool to indicate whether the event must be rejected because of spam, or a str to indicate the event must be rejected because of spam and to give a rejection reason to forward to clients.

def user_may_invite(inviter: str, invitee: str, room_id: str) -> bool

Called when processing an invitation. The module must return a bool indicating whether the inviter can invite the invitee to the given room. Both inviter and invitee are represented by their Matrix user ID (i.e. @alice:example.com).

def user_may_create_room(user: str) -> bool

Called when processing a room creation request. The module must return a bool indicating whether the given user (represented by their Matrix user ID) is allowed to create a room.

def user_may_create_room_alias(user: str, room_alias: "synapse.types.RoomAlias") -> bool

Called when trying to associate an alias with an existing room. The module must return a bool indicating whether the given user (represented by their Matrix user ID) is allowed to set the given alias.

def user_may_publish_room(user: str, room_id: str) -> bool

Called when trying to publish a room to the homeserver's public rooms directory. The module must return a bool indicating whether the given user (represented by their Matrix user ID) is allowed to publish the given room.

def check_username_for_spam(user_profile: Dict[str, str]) -> bool

Called when computing search results in the user directory. The module must return a bool indicating whether the given user profile can appear in search results. The profile is represented as a dictionary with the following keys:

user_id: The Matrix ID for this user.
display_name: The user's display name.
avatar_url: The mxc:// URL to the user's avatar.

The module is given a copy of the original dictionary, so modifying it from within the module cannot modify a user's profile when included in user directory search results.

def check_registration_for_spam(
    email_threepid: Optional[dict],
    username: Optional[str],
    request_info: Collection[Tuple[str, str]],
    auth_provider_id: Optional[str] = None,
) -> "synapse.spam_checker_api.RegistrationBehaviour"

Called when registering a new user. The module must return a RegistrationBehaviour indicating whether the registration can go through or must be denied, or whether the user may be allowed to register but will be shadow banned.

The arguments passed to this callback are:

email_threepid: The email address used for registering, if any.
username: The username the user would like to register. Can be None, meaning that Synapse will generate one later.
request_info: A collection of tuples, which first item is a user agent, and which second item is an IP address. These user agents and IP addresses are the ones that were used during the registration process.
auth_provider_id: The identifier of the SSO authentication provider, if any.

def check_media_file_for_spam(
    file_wrapper: "synapse.rest.media.v1.media_storage.ReadableFileWrapper",
    file_info: "synapse.rest.media.v1._base.FileInfo"
) -> bool

Called when storing a local or remote file. The module must return a boolean indicating whether the given file can be stored in the homeserver's media store.

Porting an existing module that uses the old interface

In order to port a module that uses Synapse's old module interface, its author needs to:

ensure the module's callbacks are all asynchronous.
register their callbacks using one or more of the register_[...]_callbacks methods from the ModuleApi class in the module's __init__ method (see this section for more info).

Additionally, if the module is packaged with an additional web resource, the module should register this resource in its __init__ method using the register_web_resource method from the ModuleApi class (see this section for more info).

The module's author should also update any example in the module's configuration to only use the new modules section in Synapse's configuration file (see this section for more info).

Example

The example below is a module that implements the spam checker callback user_may_create_room to deny room creation to user @evilguy:example.com, and registers a web resource to the path /_synapse/client/demo/hello that returns a JSON object.

import json

from twisted.web.resource import Resource
from twisted.web.server import Request

from synapse.module_api import ModuleApi


class DemoResource(Resource):
    def __init__(self, config):
        super(DemoResource, self).__init__()
        self.config = config

    def render_GET(self, request: Request):
        name = request.args.get(b"name")[0]
        request.setHeader(b"Content-Type", b"application/json")
        return json.dumps({"hello": name})


class DemoModule:
    def __init__(self, config: dict, api: ModuleApi):
        self.config = config
        self.api = api

        self.api.register_web_resource(
            path="/_synapse/client/demo/hello",
            resource=DemoResource(self.config),
        )

        self.api.register_spam_checker_callbacks(
            user_may_create_room=self.user_may_create_room,
        )

    @staticmethod
    def parse_config(config):
        return config

    async def user_may_create_room(self, user: str) -> bool:
        if user == "@evilguy:example.com":
            return False

        return True

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