Require that server names must be hostnames, and nicks cannot be hostnames

irc/net.go

@@ -27,3 +27,28 @@ func LookupHostname(addr Name) Name {
 	hostname := strings.TrimSuffix(names[0], ".")
 	return Name(hostname)
 }
+
+var allowedHostnameChars = "abcdefghijklmnopqrstuvwxyz1234567890-."
+
+func IsHostname(name string) bool {
+	// IRC hostnames specifically require a period
+	if !strings.Contains(name, ".") || len(name) < 1 || len(name) > 253 {
+		return false
+	}
+
+	// ensure each part of hostname is valid
+	for _, part := range strings.Split(name, ".") {
+		if len(part) < 1 || len(part) > 63 || strings.HasPrefix(part, "-") || strings.HasSuffix(part, "-") {
+			return false
+		}
+	}
+
+	// ensure all chars of hostname are valid
+	for _, char := range strings.Split(strings.ToLower(name), "") {
+		if !strings.Contains(allowedHostnameChars, char) {
+			return false
+		}
+	}
+
+	return true
+}