Validate IP slice values before appending or replacing

ip_slice.go

@@ -70,23 +70,35 @@ func (s *ipSliceValue) String() string {
 	return "[" + out + "]"
 }
 
-func (s *ipSliceValue) fromString(val string) net.IP {
-	return net.ParseIP(strings.TrimSpace(val))
+func (s *ipSliceValue) fromString(val string) (net.IP, error) {
+	ip := net.ParseIP(strings.TrimSpace(val))
+	if ip == nil {
+		return nil, fmt.Errorf("invalid string being converted to IP address: %s", val)
+	}
+	return ip, nil
 }
 
 func (s *ipSliceValue) toString(val net.IP) string {
 	return val.String()
 }
 
 func (s *ipSliceValue) Append(val string) error {
-	*s.value = append(*s.value, s.fromString(val))
+	ip, err := s.fromString(val)
+	if err != nil {
+		return err
+	}
+	*s.value = append(*s.value, ip)
 	return nil
 }
 
 func (s *ipSliceValue) Replace(val []string) error {
 	out := make([]net.IP, len(val))
 	for i, d := range val {
-		out[i] = s.fromString(d)
+		ip, err := s.fromString(d)
+		if err != nil {
+			return err
+		}
+		out[i] = ip
 	}
 	*s.value = out
 	return nil

ip_slice_test.go

@@ -243,3 +243,41 @@ func TestIPSBadQuoting(t *testing.T) {
 		}
 	}
 }
+
+func TestIPSliceValueRejectsInvalidIPs(t *testing.T) {
+	for _, operation := range []string{"Append", "Replace"} {
+		t.Run(operation, func(t *testing.T) {
+			var ips []net.IP
+			value := newIPSliceValue([]net.IP{net.ParseIP("192.0.2.1")}, &ips)
+			var err error
+			if operation == "Append" {
+				err = value.Append("not-an-ip")
+			} else {
+				err = value.Replace([]string{"2001:db8::1", "not-an-ip"})
+			}
+			if err == nil {
+				t.Error("expected an error for an invalid IP")
+			}
+			if len(ips) != 1 || !ips[0].Equal(net.ParseIP("192.0.2.1")) {
+				t.Errorf("invalid input changed the slice: %v", ips)
+			}
+		})
+	}
+}
+
+func TestIPSliceValueAppendAndReplace(t *testing.T) {
+	var ips []net.IP
+	value := newIPSliceValue(nil, &ips)
+	if err := value.Append(" 192.0.2.1 "); err != nil {
+		t.Fatal(err)
+	}
+	if len(ips) != 1 || !ips[0].Equal(net.ParseIP("192.0.2.1")) {
+		t.Fatalf("unexpected appended IPs: %v", ips)
+	}
+	if err := value.Replace([]string{" 2001:db8::1 "}); err != nil {
+		t.Fatal(err)
+	}
+	if len(ips) != 1 || !ips[0].Equal(net.ParseIP("2001:db8::1")) {
+		t.Fatalf("unexpected replacement IPs: %v", ips)
+	}
+}