Fix pkg/plugins TLSConfig panic

Fix #25046

Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>

pkg/plugins/discovery.go

@@ -116,7 +116,7 @@ func readPluginJSONInfo(name, path string) (*Plugin, error) {
 		return nil, err
 	}
 	p.name = name
-	if len(p.TLSConfig.CAFile) == 0 {
+	if p.TLSConfig != nil && len(p.TLSConfig.CAFile) == 0 {
 		p.TLSConfig.InsecureSkipVerify = true
 	}
 	p.activateWait = sync.NewCond(&sync.Mutex{})

pkg/plugins/discovery_test.go

@@ -117,3 +117,36 @@ func TestFileJSONSpecPlugin(t *testing.T) {
 		t.Fatalf("Expected plugin Key `/usr/shared/docker/certs/example-key.pem`, got %s\n", plugin.TLSConfig.KeyFile)
 	}
 }
+
+func TestFileJSONSpecPluginWithoutTLSConfig(t *testing.T) {
+	tmpdir, unregister := Setup(t)
+	defer unregister()
+
+	p := filepath.Join(tmpdir, "example.json")
+	spec := `{
+  "Name": "plugin-example",
+  "Addr": "https://example.com/docker/plugin"
+}`
+
+	if err := ioutil.WriteFile(p, []byte(spec), 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	r := newLocalRegistry()
+	plugin, err := r.Plugin("example")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if plugin.name != "example" {
+		t.Fatalf("Expected plugin `plugin-example`, got %s\n", plugin.Name)
+	}
+
+	if plugin.Addr != "https://example.com/docker/plugin" {
+		t.Fatalf("Expected plugin addr `https://example.com/docker/plugin`, got %s\n", plugin.Addr)
+	}
+
+	if plugin.TLSConfig != nil {
+		t.Fatalf("Expected plugin TLSConfig nil, got %v\n", plugin.TLSConfig)
+	}
+}