feat: Add SMTPResponse type for extensions (#539)

Signed-off-by: James Hillyerd <james@hillyerd.com>

pkg/extension/luahost/bind_smtpresponse_test.go

@@ -0,0 +1,40 @@
+package luahost
+
+import (
+	"testing"
+
+	"github.com/inbucket/inbucket/v3/pkg/extension/event"
+	"github.com/inbucket/inbucket/v3/pkg/test"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestSMTPResponseConstructors(t *testing.T) {
+	check := func(script string, want event.SMTPResponse) {
+		t.Helper()
+		ls, _ := test.NewLuaState()
+		registerSMTPResponseType(ls)
+		require.NoError(t, ls.DoString(script))
+
+		got, err := unwrapSMTPResponse(ls.Get(-1))
+		require.NoError(t, err)
+		assert.Equal(t, &want, got)
+	}
+
+	check("return smtp.defer()", event.SMTPResponse{Action: event.ActionDefer})
+	check("return smtp.allow()", event.SMTPResponse{Action: event.ActionAllow})
+
+	// Verify deny() has default code & msg.
+	check("return smtp.deny()", event.SMTPResponse{
+		Action:    event.ActionDeny,
+		ErrorCode: 550,
+		ErrorMsg:  "Mail denied by policy",
+	})
+
+	// Verify defaults can be overridden.
+	check("return smtp.deny(123, 'bacon')", event.SMTPResponse{
+		Action:    event.ActionDeny,
+		ErrorCode: 123,
+		ErrorMsg:  "bacon",
+	})
+}