forked from MirrorHub/synapse
73743b8ad1
Document Synapse's behaviour when multiple modules register the same callback/web resource/etc. Co-authored-by: reivilibre <oliverw@matrix.org>
85 lines
No EOL
4.1 KiB
Markdown
85 lines
No EOL
4.1 KiB
Markdown
# 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](https://github.com/matrix-org/synapse/blob/master/synapse/module_api/__init__.py).
|
|
|
|
## When Synapse runs with several modules configured
|
|
|
|
If Synapse is running with other modules configured, the order each module appears in
|
|
within the `modules` section of the Synapse configuration file might restrict what it can
|
|
or cannot register. See [this section](index.html#using-multiple-modules) for more
|
|
information.
|
|
|
|
On top of the rules listed in the link above, if a callback returns a value that should
|
|
cause the current operation to fail (e.g. if a callback checking an event returns with a
|
|
value that should cause the event to be denied), Synapse will fail the operation and
|
|
ignore any subsequent callbacks that should have been run after this one.
|
|
|
|
The documentation for each callback mentions how Synapse behaves when
|
|
multiple modules implement it.
|
|
|
|
## Handling the module's configuration
|
|
|
|
A module can implement the following static method:
|
|
|
|
```python
|
|
@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:
|
|
|
|
```python
|
|
def ModuleApi.register_web_resource(path: str, resource: IResource) -> None
|
|
```
|
|
|
|
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](https://twistedmatrix.com/documents/current/api/twisted.web.resource.IResource.html)
|
|
interface (such as [Resource](https://twistedmatrix.com/documents/current/api/twisted.web.resource.Resource.html)).
|
|
|
|
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.
|
|
|
|
Modules can register callbacks using one of the module API's `register_[...]_callbacks`
|
|
methods. The callback functions are passed to these methods as keyword arguments, with
|
|
the callback name as the argument name and the function as its value. This is demonstrated
|
|
in the example below. A `register_[...]_callbacks` method exists for each category.
|
|
|
|
Callbacks for each category can be found on their respective page of the
|
|
[Synapse documentation website](https://matrix-org.github.io/synapse). |