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+Utility Process
+===============
+
+.. warning::
+  As of january 2022, this process is under heavy work, and many things can
+  evolve. Documentation might not always be as accurate as it should be.
+  Please reach to #ipc if you intent to add a new utility.
+
+The utility process is used to provide a simple way to implement IPC actor with
+some more specific sandboxing properties, in case where you don't need or want
+to deal with the extra complexity of adding a whole new process type but you
+just want to apply different sandboxing policies.
+To implement such an actor, you will have to follow a few steps like for
+implementing the trivial example visible in `EmptyUtil
+<https://phabricator.services.mozilla.com/D126402>`_:
+
+  - Define a new IPC actor, e.g., ``PEmptyUtil`` that allows to get some string
+    via ``GetSomeString()`` from the child to the parent
+
+  - In the ``PUtilityProcess`` definition, expose a new child-level method,
+    e.g., ``StartEmptyUtilService(Endpoint<PEmptyUtilChild>)``
+
+  - Implement ``EmptyUtilChild`` and ``EmptyUtilParent`` classes both deriving
+    from their ``PEmptyUtilXX``. If you want or need to run things from a
+    different thread, you can have a look at ``UtilityProcessGenericActor``
+
+  - Make sure both are refcounted
+
+  - Expose your new service on ``UtilityProcessManager`` with a method
+    performing the heavy lifting of starting your process, you can take
+    inspiration from ``StartEmptyUtil()`` in the sample.
+
+  - Ideally, this starting method should rely on `StartUtility() <https://searchfox.org/mozilla-central/rev/fb511723f821ceabeea23b123f1c50c9e93bde9d/ipc/glue/UtilityProcessManager.cpp#210-258,266>`_
+
+  - To use ``StartUtility()`` mentioned above, please ensure that you provide
+    a ``nsresult BindToUtilityProcess(RefPtr<UtilityProcessParent>
+    aUtilityParent)``. Usually, it should be in charge of creating a set of
+    endpoints and performing ``Bind()`` to setup the IPC. You can see some example for `Utility AudioDecoder <https://searchfox.org/mozilla-central/rev/4b3039b48c3cb67774270ebcc2a7d8624d888092/ipc/glue/UtilityAudioDecoderChild.h#31-51>`_
+
+  - For proper user-facing exposition in ``about:processes`` you will have to also provide an actor
+    name via a method ``UtilityActorName GetActorName() { return UtilityActorName::EmptyUtil; }``
+
+    + Add member within `enum WebIDLUtilityActorName in <https://searchfox.org/mozilla-central/rev/fb511723f821ceabeea23b123f1c50c9e93bde9d/dom/chrome-webidl/ChromeUtils.webidl#686-689>`_
+
+  - Handle reception of ``StartEmptyUtilService`` on the child side of
+    ``UtilityProcess`` within ``RecvStartEmptyUtilService()``
+
+  - In ``UtilityProcessChild::ActorDestroy``, release any resources that
+    you stored a reference to in ``RecvStartEmptyUtilService()``.  This
+    will probably include a reference to the ``EmptyUtilChild``.
+
+  - The specific sandboxing requirements can be implemented by tracking
+    ``SandboxingKind``, and it starts within `UtilityProcessSandboxing header
+    <https://searchfox.org/mozilla-central/source/ipc/glue/UtilityProcessSandboxing.h>`_
+
+  - Try and make sure you at least add some ``gtest`` coverage of your new
+    actor, for example like in `existing gtest
+    <https://searchfox.org/mozilla-central/source/ipc/glue/test/gtest/TestUtilityProcess.cpp>`_
+
+  - Also ensure actual sandbox testing within
+
+    + ``SandboxTest`` to start your new process,
+      `<https://searchfox.org/mozilla-central/source/security/sandbox/common/test/SandboxTest.cpp>`_
+
+    + ``SandboxTestingChildTests`` to define the test
+      `<https://searchfox.org/mozilla-central/source/security/sandbox/common/test/SandboxTestingChildTests.h>`_
+
+    + ``SandboxTestingChild`` to run your test
+      `<https://searchfox.org/mozilla-central/source/security/sandbox/common/test/SandboxTestingChild.cpp>`_