// when reading from the transport.
	// If zero, a default (currently 4KB) is used.
	ReadBufferSize int

	// nextProtoOnce guards initialization of TLSNextProto and
	// h2transport (via onceSetNextProtoDefaults)
	nextProtoOnce      sync.Once
	h2transport        h2Transport // non-nil if http2 wired up
	tlsNextProtoWasNil bool        // whether TLSNextProto was nil when the Once fired