connectExtension function

Future<KernelClientConnection> connectExtension(KernelClientHost? clientHost, { required String id, required ClientTransport transport, })

Canonical way to drive the extension-transport seam off a — possibly null, possibly non-capable — clientHost. Probes ExtensionTransportConnect and injects transport, or throws a StateError if the host cannot.

Hosts (AppPlayer core, Studio backbone) and the extension_transport recipe call this instead of hand-rolling the probe. The explicit cast is required because ExtensionTransportConnect is unrelated to the declared KernelClientHost?, so an is test does not promote the variable — a footgun this helper hides in one place.

Implementation

Future<KernelClientConnection> connectExtension(
  KernelClientHost? clientHost, {
  required String id,
  required ClientTransport transport,
}) async {
  if (clientHost is! ExtensionTransportConnect) {
    throw StateError(
      'client host does not support injected extension transports '
      '(not an ExtensionTransportConnect; the kernel booted without one, '
      'or with a host that only drives kernel-built transports)',
    );
  }
  return (clientHost as ExtensionTransportConnect)
      .connectWith(id: id, transport: transport);
}