fix(unikernels): skip network args in Mewz CommandString when no network

Mewz.CommandString() unconditionally formatted ip=%s/%d and gateway=%s
even when no network was configured, producing "ip=/0 gateway= " as
kernel boot parameters. Mewz does not handle this case and panics.

Guard the network args behind an m.Net.Address != "" check, matching
the existing pattern in Hermit.CommandString(). Add unit tests covering
both the no-network and with-network cases.

Signed-off-by: mdryaan <alikhurshid4u@gmail.com>
Signed-off-by: mdryaan <alikhurshid842001@gmail.com>

fix(unikernels): simplify CommandString and use table-driven tests

PR: #674
Signed-off-by: mdryaan <alikhurshid842001@gmail.com>
Reviewed-by: Charalampos Mainas <cmainas@nubificus.co.uk>
Approved-by: Charalampos Mainas <cmainas@nubificus.co.uk>

Author: mdryaan

pkg/unikontainers/unikernels/mewz.go

@@ -36,8 +36,10 @@ type MewzNet struct {
 }
 
 func (m *Mewz) CommandString() (string, error) {
-	return fmt.Sprintf("ip=%s/%d gateway=%s ", m.Net.Address, m.Net.Mask,
-		m.Net.Gateway), nil
+	if m.Net.Address != "" {
+		return fmt.Sprintf("ip=%s/%d gateway=%s", m.Net.Address, m.Net.Mask, m.Net.Gateway), nil
+	}
+	return "", nil
 }
 
 func (m *Mewz) SupportsBlock() bool {

pkg/unikontainers/unikernels/mewz_test.go

@@ -0,0 +1,58 @@
+// Copyright (c) 2023-2026, Nubificus LTD
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package unikernels
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestMewzCommandString(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name     string
+		mewz     *Mewz
+		expected string
+	}{
+		{
+			name:     "no network configured",
+			mewz:     &Mewz{},
+			expected: "",
+		},
+		{
+			name: "with network configured",
+			mewz: &Mewz{
+				Net: MewzNet{
+					Address: "10.0.0.2",
+					Mask:    24,
+					Gateway: "10.0.0.1",
+				},
+			},
+			expected: "ip=10.0.0.2/24 gateway=10.0.0.1",
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			result, err := tc.mewz.CommandString()
+			require.NoError(t, err)
+			assert.Equal(t, tc.expected, result)
+		})
+	}
+}