id: add utilities for validating server names

id/servername.go

@@ -0,0 +1,58 @@
+// Copyright (c) 2025 Tulir Asokan
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+package id
+
+import (
+	"regexp"
+	"strconv"
+)
+
+type ParsedServerNameType int
+
+const (
+	ServerNameDNS ParsedServerNameType = iota
+	ServerNameIPv4
+	ServerNameIPv6
+)
+
+type ParsedServerName struct {
+	Type ParsedServerNameType
+	Host string
+	Port int
+}
+
+var ServerNameRegex = regexp.MustCompile(`^(?:\[([0-9A-Fa-f:.]{2,45})]|(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})|([0-9A-Za-z.-]{1,255}))(\d{1,5})?$`)
+
+func ValidateServerName(serverName string) bool {
+	return len(serverName) <= 255 && len(serverName) > 0 && ServerNameRegex.MatchString(serverName)
+}
+
+func ParseServerName(serverName string) *ParsedServerName {
+	if len(serverName) > 255 || len(serverName) < 1 {
+		return nil
+	}
+	match := ServerNameRegex.FindStringSubmatch(serverName)
+	if len(match) != 5 {
+		return nil
+	}
+	port, _ := strconv.Atoi(match[4])
+	parsed := &ParsedServerName{
+		Port: port,
+	}
+	switch {
+	case match[1] != "":
+		parsed.Type = ServerNameIPv6
+		parsed.Host = match[1]
+	case match[2] != "":
+		parsed.Type = ServerNameIPv4
+		parsed.Host = match[2]
+	case match[3] != "":
+		parsed.Type = ServerNameDNS
+		parsed.Host = match[3]
+	}
+	return parsed
+}