PROTOCOLS

ComponentController

Defined in fuchsia.component.runner/component_runner.fidl

A protocol for binding and controlling the lifetime of a component instance started using ComponentRunner.Start(). The component manager is the intended direct client of this protocol.

When the controlled component instance terminates or becomes inaccessible for any reason, the server closes the connection with an epitaph.

LIFECYCLE

A component may exist in one of two states: Started, or Stopped. The component is Started from the time ComponentRunner.Start() is called until the ComponentRunner closes the ComponentController handle. The component then transitions to Stopped.

Component manager uses ComponentController to terminate a component in two steps:

1. Component manager calls Stop() to indicate that the ComponentRunner should stop a component's execution and close this connection with an epitaph.
2. If after some time the ComponentController is not closed, component manager calls Kill() to indicate that the ComponentRunner must halt a component's execution immediately, and then close this connection with an epitaph. The component manager may wait some period of time after calling Kill() before closing the ComponentController channel, but makes no guarantees it will wait or for how long.

Component manager first waits for the ComponentController to close, and then tears down the namespace it hosts for the stopped component. Component manager may call Kill() without first having called Stop().

EPITAPH

This protocol sends a FIDL epitaph to indicate that the component instance has been terminated. The component runner is expected to clean up all resources attributed to the component before closing the connection.

The following epitaphs may be sent by the server on error:

• ZX_OK: The component exited successfully, typically because the component was asked to stop or it decided independently to exit.
• INVALID_ARGUMENTS:
  • start_info.resolved_url is not supported by this runner;
  • start_info contains missing or invalid arguments.
• INSTANCE_CANNOT_START: The runner could not start the component. For example, a critical part of the program could not be found or loaded, or the referenced binary was invalid for this runner.
• RESOURCE_UNAVAILABLE: The component could not be launched due to lack of resources.
• INTERNAL: An unexpected internal runner error was encountered.
• INSTANCE_DIED: The component instance was started but subsequently terminated with an error.
• Other status codes (e.g. ZX_ERR_PEER_CLOSED) may indicate a failure of the component runner itself. The component manager may respond to such failures by terminating the component runner's job to ensure system stability.

Kill

Stop this component instance immediately.

The ComponentRunner must immediately kill the component instance, and then close this connection with an epitaph. After the connection closes, component manager considers this component instance to be Stopped and the component's namespace will be torn down.

In some cases Kill() may be issued before Stop(), but that is not guaranteed.

Request

<EMPTY>

OnPublishDiagnostics

Event for runners to publish diagnostics to the platform.

This event signals to the platform that the runner for this component is publishing diagnostics about the runtime of the component. The component manager may optionally expose this data to clients.

Response

Name	Type
payload	fuchsia.diagnostics.types/ComponentDiagnostics

Stop

Request to stop the component instance.

After stopping the component instance, the server should close this connection with an epitaph. After the connection closes, component manager considers this component instance to be Stopped and the component's namespace will be torn down.

Request

<EMPTY>

ComponentRunner

Defined in fuchsia.component.runner/component_runner.fidl

A protocol used for running components.

This protocol is implemented by components which provide a runtime environment for other components.

Note: The component manager is the only intended direct client of this interface.

Start

Start running a component instance described by start_info.

Component manager binds and uses controller to control the lifetime of the newly started component instance.

Errors are delivered as epitaphs over the ComponentController protocol. In the event of an error, the runner must ensure that resources are cleaned up.

Errors:

Request

Name	Type
start_info	ComponentStartInfo
controller	server_end<ComponentController>

TABLES

ComponentNamespaceEntry resource

Defined in fuchsia.component.runner/component_runner.fidl

A single component namespace entry, which describes a namespace mount point (path) and the directory backing it (directory). This type is usually composed inside a vector. See ComponentStartInfo.ns for more details.

Ordinal	Field	Type	Description
1	path	string[4095]	The mount point for the directory, including a leading slash. For example: "/pkg", "/svc", or "/config/data".
2	directory	fuchsia.io/Directory	The directory mounted at the above path.

ComponentStartInfo resource

Defined in fuchsia.component.runner/component_runner.fidl

Parameters for starting a new component instance.

Ordinal	Field	Type	Description
1	resolved_url	fuchsia.url/Url	The resolved URL of the component. This is the canonical URL obtained by the component resolver after following redirects and resolving relative paths.
2	program	fuchsia.data/Dictionary	The component's program declaration. This information originates from ComponentDecl.program.
3	ns	vector<ComponentNamespaceEntry>[32]	The namespace to provide to the component instance. A namespace specifies the set of directories that a component instance receives at start-up. Through the namespace directories, a component may access capabilities available to it. The contents of the namespace are mainly determined by the component's use declarations but may also contain additional capabilities automatically provided by the framework. By convention, a component's namespace typically contains some or all of the following directories: "/svc": A directory containing services that the component requested to use via its "import" declarations. "/pkg": A directory containing the component's package, including its binaries, libraries, and other assets. The mount points specified in each entry must be unique and non-overlapping. For example, [{"/foo", ..}, {"/foo/bar", ..}] is invalid.
4	outgoing_dir	server_end<fuchsia.io/Directory>	The directory this component serves.
5	runtime_dir	server_end<fuchsia.io/Directory>	The directory served by the runner to present runtime information about the component. The runner must either serve it, or drop it to avoid blocking any consumers indefinitely.
6	numbered_handles	vector<fuchsia.process/HandleInfo>[128]	The numbered handles that were passed to the component. If the component does not support numbered handles, the runner is expected to close the handles.
7	encoded_config	fuchsia.mem/Data	Binary representation of the component's configuration. Layout The first 2 bytes of the data should be interpreted as an unsigned 16-bit little-endian integer which denotes the number of bytes following it that contain the configuration checksum. After the checksum, all the remaining bytes are a persistent FIDL message of a top-level struct. The struct's fields match the configuration fields of the component's compiled manifest in the same order.
8	break_on_start	handle<eventpair>	An eventpair that debuggers can use to defer the launch of the component. For example, ELF runners hold off from creating processes in the component until ZX_EVENTPAIR_PEER_CLOSED is signaled on this eventpair. They also ensure that runtime_dir is served before waiting on this eventpair. ELF debuggers can query the runtime_dir to decide whether to attach before they drop the other side of the eventpair, which is sent in the payload of the DebugStarted event in fuchsia.component.events.

CONSTANTS

Name	Value	Type	Description
MAX_HANDLE_COUNT	128	uint32
MAX_NAMESPACE_COUNT	32	uint32