feat: Add SMTPResponse type for extensions (#539)

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

pkg/extension/luahost/bind_smtpresponse.go

@@ -0,0 +1,54 @@
+package luahost
+
+import (
+	"fmt"
+
+	"github.com/inbucket/inbucket/v3/pkg/extension/event"
+	lua "github.com/yuin/gopher-lua"
+)
+
+const smtpResponseName = "smtp"
+
+func registerSMTPResponseType(ls *lua.LState) {
+	mt := ls.NewTypeMetatable(smtpResponseName)
+	ls.SetGlobal(smtpResponseName, mt)
+
+	// Static attributes.
+	ls.SetField(mt, "allow", ls.NewFunction(newSMTPResponse(event.ActionAllow)))
+	ls.SetField(mt, "defer", ls.NewFunction(newSMTPResponse(event.ActionDefer)))
+	ls.SetField(mt, "deny", ls.NewFunction(newSMTPResponse(event.ActionDeny)))
+}
+
+func newSMTPResponse(action int) func(*lua.LState) int {
+	return func(ls *lua.LState) int {
+		val := &event.SMTPResponse{Action: action}
+
+		if action == event.ActionDeny {
+			// Optionally accept error code and message.
+			val.ErrorCode = ls.OptInt(1, 550)
+			val.ErrorMsg = ls.OptString(2, "Mail denied by policy")
+		}
+
+		ud := wrapSMTPResponse(ls, val)
+		ls.Push(ud)
+		return 1
+	}
+}
+
+func wrapSMTPResponse(ls *lua.LState, val *event.SMTPResponse) *lua.LUserData {
+	ud := ls.NewUserData()
+	ud.Value = val
+	ls.SetMetatable(ud, ls.GetTypeMetatable(smtpResponseName))
+
+	return ud
+}
+
+func unwrapSMTPResponse(lv lua.LValue) (*event.SMTPResponse, error) {
+	if ud, ok := lv.(*lua.LUserData); ok {
+		if v, ok := ud.Value.(*event.SMTPResponse); ok {
+			return v, nil
+		}
+	}
+
+	return nil, fmt.Errorf("expected SMTPResponse, got %q", lv.Type().String())
+}