feat: Enhance AddEntries and RemoveByHostname functions with subdomain and alias handling

hostfile/managed.go

@@ -57,6 +57,19 @@ func ParseManagedBlock(lines []string) (prefix, managed, postfix []string, hasMa
 	return prefix, managed, postfix, true, nil
 }
 
+// lineMatchesHostname parses a hosts-file line ("IP<whitespace>hostname [aliases...]")
+// and returns true if any hostname field (including aliases) matches,
+// using case-insensitive comparison per RFC 4343.
+func lineMatchesHostname(line, hostname string) bool {
+	fields := strings.Fields(line)
+	for _, f := range fields[1:] {
+		if strings.EqualFold(f, hostname) {
+			return true
+		}
+	}
+	return false
+}
+
 // AddEntries removes existing entries for the same hostnames as the new entries,
 // then appends the new entries. Returns deduplicated managed content lines.
 func AddEntries(existing []string, entries []DNSEntry) []string {
@@ -71,7 +84,7 @@ func AddEntries(existing []string, entries []DNSEntry) []string {
 	for _, line := range existing {
 		keep := true
 		for h := range hostnames {
-			if strings.Contains(line, h) {
+			if lineMatchesHostname(line, h) {
 				keep = false
 				break
 			}
@@ -101,7 +114,7 @@ func RemoveByHostname(existing []string, hostnames []string) []string {
 	for _, line := range existing {
 		shouldRemove := false
 		for _, host := range hostnames {
-			if strings.Contains(line, host) {
+			if lineMatchesHostname(line, host) {
 				shouldRemove = true
 				break
 			}