onRequest method
Called when the request is about to be sent.
Implementation
@override
void onRequest(RequestOptions options, RequestInterceptorHandler handler) {
final id = HttpTracker.instance.startRequest(
options.method,
options.uri.toString(),
requestBytes: options.data is List<int>
? (options.data as List<int>).length
: null,
);
options.extra[_extraKey] = id;
handler.next(options);
}