lib/options: BlacklistIP text encoding

The BlacklistIP configuration uses the CIDR notation.
Implemented the TextMarshaler interface to support correct
encoding based on the notation.

lib/options.go

@@ -28,10 +28,9 @@ import (
 	"reflect"
 	"strconv"
 
-	"gopkg.in/guregu/null.v3"
-
 	"go.k6.io/k6/lib/types"
 	"go.k6.io/k6/stats"
+	"gopkg.in/guregu/null.v3"
 )
 
 // DefaultScenarioName is used as the default key/ID of the scenario config entries
@@ -178,10 +177,14 @@ func (ipnet *IPNet) UnmarshalText(b []byte) error {
 	}
 
 	*ipnet = *newIPNet
-
 	return nil
 }
 
+// MarshalText encodes the IPNet representation using CIDR notation.
+func (ipnet *IPNet) MarshalText() ([]byte, error) {
+	return []byte(ipnet.String()), nil
+}
+
 // HostAddress stores information about IP and port
 // for a host.
 type HostAddress net.TCPAddr

lib/options_test.go

@@ -307,15 +307,28 @@ func TestOptions(t *testing.T) {
 		opts := Options{}.Apply(Options{
 			BlacklistIPs: []*IPNet{{
 				IPNet: net.IPNet{
-					IP:   net.IPv4zero,
-					Mask: net.CIDRMask(1, 1),
+					IP:   net.IPv4bcast,
+					Mask: net.CIDRMask(31, 32),
 				},
 			}},
 		})
 		assert.NotNil(t, opts.BlacklistIPs)
 		assert.NotEmpty(t, opts.BlacklistIPs)
-		assert.Equal(t, net.IPv4zero, opts.BlacklistIPs[0].IP)
-		assert.Equal(t, net.CIDRMask(1, 1), opts.BlacklistIPs[0].Mask)
+		assert.Equal(t, net.IPv4bcast, opts.BlacklistIPs[0].IP)
+		assert.Equal(t, net.CIDRMask(31, 32), opts.BlacklistIPs[0].Mask)
+
+		t.Run("JSON", func(t *testing.T) {
+			t.Parallel()
+
+			b, err := json.Marshal(opts)
+			require.NoError(t, err)
+
+			var uopts Options
+			err = json.Unmarshal(b, &uopts)
+			require.NoError(t, err)
+			require.Len(t, uopts.BlacklistIPs, 1)
+			require.Equal(t, "255.255.255.254/31", uopts.BlacklistIPs[0].String())
+		})
 	})
 	t.Run("BlockedHostnames", func(t *testing.T) {
 		blockedHostnames, err := types.NewNullHostnameTrie([]string{"test.k6.io", "*valid.pattern"})