Introduce `InsertUnique()`

iptables/iptables.go

@@ -185,6 +185,20 @@ func (ipt *IPTables) Insert(table, chain string, pos int, rulespec ...string) er
 	return ipt.run(cmd...)
 }
 
+// InsertUnique acts like Insert except that it won't insert a duplicate (no matter the position in the chain)
+func (ipt *IPTables) InsertUnique(table, chain string, pos int, rulespec ...string) error {
+	exists, err := ipt.Exists(table, chain, rulespec...)
+	if err != nil {
+		return err
+	}
+
+	if !exists {
+		return ipt.Insert(table, chain, pos, rulespec...)
+	}
+
+	return nil
+}
+
 // Append appends rulespec to specified table/chain
 func (ipt *IPTables) Append(table, chain string, rulespec ...string) error {
 	cmd := append([]string{"-t", table, "-A", chain}, rulespec...)

iptables/iptables_test.go

@@ -293,6 +293,11 @@ func runRulesTests(t *testing.T, ipt *IPTables) {
 		t.Fatalf("Insert failed: %v", err)
 	}
 
+	err = ipt.InsertUnique("filter", chain, 2, "-s", subnet2, "-d", address2, "-j", "ACCEPT")
+	if err != nil {
+		t.Fatalf("Insert failed: %v", err)
+	}
+
 	err = ipt.Insert("filter", chain, 1, "-s", subnet1, "-d", address2, "-j", "ACCEPT")
 	if err != nil {
 		t.Fatalf("Insert failed: %v", err)