Function validDNSName

ech.go:476–499

validDNSName is a rather rudimentary check for the validity of a DNS name. This is used to check if the public_name in a ECHConfig is valid when we are picking a config. This can be somewhat lax because even if we pick a valid-looking name, the DNS layer will later reject it anyway.

(name string)

// picking a config. This can be somewhat lax because even if we pick a
// valid-looking name, the DNS layer will later reject it anyway.
func validDNSName(name string) bool {
	if len(name) > 253 {
		return false
	}
	labels := strings.Split(name, ".")
	if len(labels) <= 1 {
		return false
	}
	for _, l := range labels {
		labelLen := len(l)
		if labelLen == 0 {
			return false
		}
		for i, r := range l {
			if r == '-' && (i == 0 || i == labelLen-1) {
				return false
			}
			if (r < '0' || r > '9') && (r < 'a' || r > 'z') && (r < 'A' || r > 'Z') && r != '-' {
				return false
			}
		}
	}
	return true
}

// ECHRejectionError is the error type returned when ECH is rejected by a remote
// server. If the server offered a ECHConfigList to use for retries, the