With no configured protocols, none is negotiated and none is echoed —
echoing a protocol the client did not request breaks conformant clients.
With configured protocols, the client's first requested protocol that the
route accepts wins; if none match, the handshake is refused.
Parameters
configured: readonlystring[]
The route's accepted protocols
requested: readonlystring[]
The protocols the client asked for
Returns string|false|undefined
The selected protocol, undefined when none is negotiated, or false to refuse
Selects the subprotocol to echo for a route.
With no configured protocols, none is negotiated and none is echoed — echoing a protocol the client did not request breaks conformant clients. With configured protocols, the client's first requested protocol that the route accepts wins; if none match, the handshake is refused.