Utility Process

Warning

Please reach out to #ipc on https://chat.mozilla.org/ 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:

  • 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()

  • 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 UtilityMediaService

  • 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; }

  • 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

  • Try and make sure you at least add some gtest coverage of your new actor, for example like in existing gtest

  • Also ensure actual sandbox testing within

  • Please also consider having a look at Process Bookkeeping for anything you may want to ensure is supported by your new process, like e.g. profiler, crash reporting, etc.