sdk/fidl/fuchsia.sys2/realm.fidl

// Copyright 2018 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

library fuchsia.sys2;

using fuchsia.io;

// An interface used by a component instance to manage its own realm,
// such as for binding to its children.
//
// Note: The component manager exposes this interface to components
// that import the "fuchsia.sys2.Realm" service.
[Discoverable]
protocol Realm {
    // Binds to a child component instance, causing it to start running if
    // it is not already running.
    //
    // |child_name| must be the name of an already declared child in the realm.
    // |binding| is bound to the child.
    BindChild(string child_name, request<ComponentBinding> binding);

    // TODO(CP-154): Dynamically add/remove children in collections.
    // Perhaps have a way to control their durability.
    //2: AddChild(string collection_name, ChildDecl decl);
    //3: RemoveChild(string collection_name, string child_name);

    // TODO(CP-154): Add methods for resolving packages and components
    // within the realm.
};

// An interface that retains a connection to a component instance.
//
// Holding a binding is an indication to the component manager that the
// bound component instance is providing a useful service on behalf of
// the component instance that requested the binding.
//
// A component instance may retained by multiple bindings simultaneously.
// Typically this means that the component instance will continue to run
// until one of the following occurs:
//
// - All of the bindings retaining the component have been released.
// - The component instance terminates (or crashes).
// - The component instance is removed from its parent.
// - The component instance is killed due to component management policies
//   such as software updates or reallocation of system resources.
//
// EPITAPH
//
// This interface uses a FIDL epitaph to indicate that the bound component
// instance has terminated and to describe its final disposition.
//
// The following epitaph status codes have particular significance:
//
// - |ZX_ERR_NOT_FOUND|: The component instance named in the call to
//   |Realm.BindChild()| does not exist.
// - |ZX_ERR_UNAVAILABLE|: The component instance could not be started.
// - |ERR_COMPONENT_DIED|: The component instance was started but
//   subsequently terminated unexpectedly.
//
// Other status codes (e.g. |ZX_ERR_PEER_CLOSED|) may indicate a failure
// of the component manager itself.
protocol ComponentBinding {
    // Gets a directory containing objects exported by the child.
    GetExports(request<fuchsia.io.Directory> exports);

    // TODO(CP-154): Provide a mechanism to apply hints to a binding to
    // modulate its retention and resource allocation characteristics.
};