Takes control of the underlying request socket.
Synchronously, this throws a HijackException that indicates to the
adapter that it shouldn't emit a response itself. Asynchronously,
callback is called with a Stream and
StreamSink, respectively, that provide access to the
underlying request socket.
If the sink is closed, the stream will be closed as well. The stream and
sink may be the same object, as in the case of a dart:io Socket
object.
This may only be called when using a Shelf adapter that supports
hijacking, such as the dart:io adapter. In addition, a given request may
only be hijacked once. canHijack can be used to detect whether this
request can be hijacked.
Source
void hijack(HijackCallback callback) {
if (_onHijack == null) {
throw new StateError("This request can't be hijacked.");
}
_onHijack.run(callback);
throw const HijackException();
}