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<ol class="chapter"><li class="chapter-item expanded affix "><li class="part-title">Introduction</li><li class="chapter-item expanded "><a href="../welcome_and_overview.html">Welcome and Overview</a></li><li class="chapter-item expanded affix "><li class="part-title">Setup</li><li class="chapter-item expanded "><a href="../setup/installation.html">Installation</a></li><li class="chapter-item expanded "><a href="../postgres.html">Using Postgres</a></li><li class="chapter-item expanded "><a href="../reverse_proxy.html">Configuring a Reverse Proxy</a></li><li class="chapter-item expanded "><a href="../setup/forward_proxy.html">Configuring a Forward/Outbound Proxy</a></li><li class="chapter-item expanded "><a href="../turn-howto.html">Configuring a Turn Server</a></li><li class="chapter-item expanded "><a href="../delegate.html">Delegation</a></li><li class="chapter-item expanded affix "><li class="part-title">Upgrading</li><li class="chapter-item expanded "><a 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class="active">Writing a module</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../modules/spam_checker_callbacks.html">Spam checker callbacks</a></li><li class="chapter-item expanded "><a href="../modules/third_party_rules_callbacks.html">Third-party rules callbacks</a></li><li class="chapter-item expanded "><a href="../modules/presence_router_callbacks.html">Presence router callbacks</a></li><li class="chapter-item expanded "><a href="../modules/account_validity_callbacks.html">Account validity callbacks</a></li><li class="chapter-item expanded "><a href="../modules/password_auth_provider_callbacks.html">Password auth provider callbacks</a></li><li class="chapter-item expanded "><a href="../modules/background_update_controller_callbacks.html">Background update controller callbacks</a></li><li class="chapter-item expanded "><a href="../modules/account_data_callbacks.html">Account data callbacks</a></li><li class="chapter-item expanded "><a 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format</a></li><li class="chapter-item expanded "><a href="../usage/administration/admin_faq.html">Admin FAQ</a></li><li class="chapter-item expanded "><div>Scripts</div></li></ol></li><li class="chapter-item expanded "><li class="part-title">Development</li><li class="chapter-item expanded "><a href="../development/contributing_guide.html">Contributing Guide</a></li><li class="chapter-item expanded "><a href="../code_style.html">Code Style</a></li><li class="chapter-item expanded "><a href="../development/releases.html">Release Cycle</a></li><li class="chapter-item expanded "><a href="../development/git.html">Git Usage</a></li><li class="chapter-item expanded "><div>Testing</div></li><li><ol class="section"><li class="chapter-item expanded "><a href="../development/demo.html">Demo scripts</a></li></ol></li><li class="chapter-item expanded "><a href="../opentracing.html">OpenTracing</a></li><li class="chapter-item expanded "><a href="../development/database_schema.html">Database 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<h1 id="writing-a-module"><a class="header" href="#writing-a-module">Writing a module</a></h1>
<p>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.</p>
<p>When instantiated, a module is given its parsed configuration as well as an instance of
the <code>synapse.module_api.ModuleApi</code> class. The configuration is a dictionary, and is
either the output of the module's <code>parse_config</code> static method (see below), or the
configuration associated with the module in Synapse's configuration file.</p>
<p>See the documentation for the <code>ModuleApi</code> class
<a href="https://github.com/matrix-org/synapse/blob/master/synapse/module_api/__init__.py">here</a>.</p>
<h2 id="when-synapse-runs-with-several-modules-configured"><a class="header" href="#when-synapse-runs-with-several-modules-configured">When Synapse runs with several modules configured</a></h2>
<p>If Synapse is running with other modules configured, the order each module appears in
within the <code>modules</code> section of the Synapse configuration file might restrict what it can
or cannot register. See <a href="index.html#using-multiple-modules">this section</a> for more
information.</p>
<p>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.</p>
<p>The documentation for each callback mentions how Synapse behaves when
multiple modules implement it.</p>
<h2 id="handling-the-modules-configuration"><a class="header" href="#handling-the-modules-configuration">Handling the module's configuration</a></h2>
<p>A module can implement the following static method:</p>
<pre><code class="language-python">@staticmethod
def parse_config(config: dict) -> Any
</code></pre>
<p>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
<code>synapse.module_api.errors.ConfigError</code> if not.</p>
<h2 id="registering-a-web-resource"><a class="header" href="#registering-a-web-resource">Registering a web resource</a></h2>
<p>Modules can register web resources onto Synapse's web server using the following module
API method:</p>
<pre><code class="language-python">def ModuleApi.register_web_resource(path: str, resource: IResource) -> None
</code></pre>
<p>The path is the full absolute path to register the resource at. For example, if you
register a resource for the path <code>/_synapse/client/my_super_module/say_hello</code>, Synapse
will serve it at <code>http(s)://[HS_URL]/_synapse/client/my_super_module/say_hello</code>. Note
that Synapse does not allow registering resources for several sub-paths in the <code>/_matrix</code>
namespace (such as anything under <code>/_matrix/client</code> for example). It is strongly
recommended that modules register their web resources under the <code>/_synapse/client</code>
namespace.</p>
<p>The provided resource is a Python class that implements Twisted's <a href="https://twistedmatrix.com/documents/current/api/twisted.web.resource.IResource.html">IResource</a>
interface (such as <a href="https://twistedmatrix.com/documents/current/api/twisted.web.resource.Resource.html">Resource</a>).</p>
<p>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.</p>
<p>Modules <strong>must</strong> register their web resources in their <code>__init__</code> method.</p>
<h2 id="registering-a-callback"><a class="header" href="#registering-a-callback">Registering a callback</a></h2>
<p>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 (unless
specified otherwise), 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.</p>
<p>Modules can register callbacks using one of the module API's <code>register_[...]_callbacks</code>
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. A
<code>register_[...]_callbacks</code> method exists for each category.</p>
<p>Callbacks for each category can be found on their respective page of the
<a href="https://matrix-org.github.io/synapse">Synapse documentation website</a>.</p>
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