feat: Add SMTPSession and BeforeRcptToAccepted event (#541)

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

pkg/extension/luahost/bind_smtpsession.go

@@ -0,0 +1,70 @@
+package luahost
+
+import (
+	"github.com/inbucket/inbucket/v3/pkg/extension/event"
+	lua "github.com/yuin/gopher-lua"
+)
+
+const smtpSessionName = "smtp_session"
+
+func registerSMTPSessionType(ls *lua.LState) {
+	mt := ls.NewTypeMetatable(smtpSessionName)
+	ls.SetGlobal(smtpSessionName, mt)
+
+	// Static attributes.
+	ls.SetField(mt, "new", ls.NewFunction(newSMTPSession))
+
+	// Methods.
+	ls.SetField(mt, "__index", ls.NewFunction(smtpSessionIndex))
+}
+
+func newSMTPSession(ls *lua.LState) int {
+	val := &event.SMTPSession{}
+	ud := wrapSMTPSession(ls, val)
+	ls.Push(ud)
+
+	return 1
+}
+
+func wrapSMTPSession(ls *lua.LState, val *event.SMTPSession) *lua.LUserData {
+	ud := ls.NewUserData()
+	ud.Value = val
+	ls.SetMetatable(ud, ls.GetTypeMetatable(smtpSessionName))
+
+	return ud
+}
+
+// Checks there is an SMTPSession at stack position `pos`, else throws Lua error.
+func checkSMTPSession(ls *lua.LState, pos int) *event.SMTPSession {
+	ud := ls.CheckUserData(pos)
+	if v, ok := ud.Value.(*event.SMTPSession); ok {
+		return v
+	}
+	ls.ArgError(pos, smtpSessionName+" expected")
+	return nil
+}
+
+// Gets a field value from SMTPSession user object.  This emulates a Lua table,
+// allowing `msg.subject` instead of a Lua object syntax of `msg:subject()`.
+func smtpSessionIndex(ls *lua.LState) int {
+	m := checkSMTPSession(ls, 1)
+	field := ls.CheckString(2)
+
+	// Push the requested field's value onto the stack.
+	switch field {
+	case "from":
+		ls.Push(wrapMailAddress(ls, m.From))
+	case "to":
+		lt := &lua.LTable{}
+		for _, v := range m.To {
+			addr := v
+			lt.Append(wrapMailAddress(ls, addr))
+		}
+		ls.Push(lt)
+	default:
+		// Unknown field.
+		ls.Push(lua.LNil)
+	}
+
+	return 1
+}