	hello := &clientHelloMsg{
		vers:                         maxVersion,
		compressionMethods:           []uint8{compressionNone},
		random:                       make([]byte, 32),
…
		serverName:                   hostnameInSNI(config.ServerName),
		supportedCurves:              config.curvePreferences(maxVersion),
…
		alpnProtocols:                config.NextProtos,
		supportedVersions:            supportedVersions,
	}

	// The version at the beginning of the ClientHello was capped at TLS 1.2
	// for compatibility reasons. The supported_versions extension is used
	// to negotiate versions now. See RFC 8446, Section 4.2.1.
	if hello.vers > VersionTLS12 {
		hello.vers = VersionTLS12
	}
…
		// Since the order is fixed, the first one is always the one to send a
		// key share for. All the PQ hybrids sort first, and produce a fallback
		// ECDH share.
		curveID := hello.supportedCurves[0]
		ke, err := keyExchangeForCurveID(curveID)
…
		keyShareKeys, hello.keyShares, err = ke.keyShares(config.rand())
…
func hostnameInSNI(name string) string {
	host := name
	if len(host) > 0 && host[0] == '[' && host[len(host)-1] == ']' {
		host = host[1 : len(host)-1]
	}
	if i := strings.LastIndex(host, "%"); i > 0 {
		host = host[:i]
	}
	if net.ParseIP(host) != nil {
		return ""
	}
	for len(name) > 0 && name[len(name)-1] == '.' {
		name = name[:len(name)-1]
	}
	return name
}

Warm-up