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
 			}

hostfile/managed_test.go

@@ -201,6 +201,52 @@ func TestAddEntries_ReplacesExistingHostname(t *testing.T) {
 	}
 }
 
+func TestAddEntries_DoesNotClobberSubdomains(t *testing.T) {
+	// Regression: substring matching would cause adding "example.com" to
+	// incorrectly remove "sub.example.com" entries.
+	existing := []string{
+		"1.1.1.1\tsub.example.com",
+		"2.2.2.2\tother.example.com",
+	}
+	entries := []hostfile.DNSEntry{{IP: "9.9.9.9", Hostname: "example.com"}}
+	result := hostfile.AddEntries(existing, entries)
+	if len(result) != 3 {
+		t.Fatalf("expected 3 entries (2 existing + 1 new), got %d: %v", len(result), result)
+	}
+	for _, line := range result {
+		if line == "1.1.1.1\tsub.example.com" || line == "2.2.2.2\tother.example.com" || line == "9.9.9.9\texample.com" {
+			continue
+		}
+		t.Errorf("unexpected line: %q", line)
+	}
+}
+
+func TestAddEntries_MatchesAliasColumn(t *testing.T) {
+	// A hosts-file line can have aliases: "IP primary alias1 alias2"
+	// Replacing "alias1" should remove the entire line.
+	existing := []string{"1.1.1.1\tprimary\talias1"}
+	entries := []hostfile.DNSEntry{{IP: "9.9.9.9", Hostname: "alias1"}}
+	result := hostfile.AddEntries(existing, entries)
+	for _, line := range result {
+		if strings.Contains(line, "primary") {
+			t.Errorf("line with alias1 should have been removed, but found: %q", line)
+		}
+	}
+}
+
+func TestAddEntries_CaseInsensitive(t *testing.T) {
+	// RFC 4343: hostnames are case-insensitive.
+	existing := []string{"1.1.1.1\tHost1.Example.COM"}
+	entries := []hostfile.DNSEntry{{IP: "9.9.9.9", Hostname: "host1.example.com"}}
+	result := hostfile.AddEntries(existing, entries)
+	if len(result) != 1 {
+		t.Fatalf("expected 1 entry (old replaced), got %d: %v", len(result), result)
+	}
+	if result[0] != "9.9.9.9\thost1.example.com" {
+		t.Errorf("expected new entry, got %q", result[0])
+	}
+}
+
 func TestAddEntries_Deduplicates(t *testing.T) {
 	existing := []string{"1.1.1.1\thost1"}
 	entries := []hostfile.DNSEntry{
@@ -332,6 +378,54 @@ func TestRemoveByHostname_RegressionNoDuplicates(t *testing.T) {
 	}
 }
 
+func TestRemoveByHostname_DoesNotClobberSubdomains(t *testing.T) {
+	// Regression: substring matching would remove "sub.example.com" when
+	// only "example.com" was requested for removal.
+	existing := []string{
+		"1.1.1.1\texample.com",
+		"2.2.2.2\tsub.example.com",
+		"3.3.3.3\tmy-example.com",
+	}
+	result := hostfile.RemoveByHostname(existing, []string{"example.com"})
+	if len(result) != 2 {
+		t.Fatalf("expected 2 remaining entries, got %d: %v", len(result), result)
+	}
+	if result[0] != "2.2.2.2\tsub.example.com" {
+		t.Errorf("expected sub.example.com to remain, got %q", result[0])
+	}
+	if result[1] != "3.3.3.3\tmy-example.com" {
+		t.Errorf("expected my-example.com to remain, got %q", result[1])
+	}
+}
+
+func TestRemoveByHostname_MatchesAliasColumn(t *testing.T) {
+	existing := []string{
+		"1.1.1.1\tprimary\talias1",
+		"2.2.2.2\thost2",
+	}
+	result := hostfile.RemoveByHostname(existing, []string{"alias1"})
+	if len(result) != 1 {
+		t.Fatalf("expected 1 remaining entry, got %d: %v", len(result), result)
+	}
+	if result[0] != "2.2.2.2\thost2" {
+		t.Errorf("expected host2 to remain, got %q", result[0])
+	}
+}
+
+func TestRemoveByHostname_CaseInsensitive(t *testing.T) {
+	existing := []string{
+		"1.1.1.1\tHost1.Example.COM",
+		"2.2.2.2\thost2",
+	}
+	result := hostfile.RemoveByHostname(existing, []string{"host1.example.com"})
+	if len(result) != 1 {
+		t.Fatalf("expected 1 remaining entry, got %d: %v", len(result), result)
+	}
+	if result[0] != "2.2.2.2\thost2" {
+		t.Errorf("expected host2 to remain, got %q", result[0])
+	}
+}
+
 // ---------------------------------------------------------------------------
 // RemoveAll tests (T018)
 // ---------------------------------------------------------------------------