fix: middleware panics on ended transaction

module/apmechov4/middleware.go

@@ -81,7 +81,10 @@ func (m *middleware) handle(c echo.Context) error {
 	}
 	name := m.requestName(c)
 	tx, body, req := apmhttp.StartTransactionWithBody(m.tracer, name, req)
-	defer tx.End()
+	defer func() {
+		body.Discard()
+		tx.End()
+	}()
 	c.SetRequest(req)
 
 	resp := c.Response()
@@ -106,11 +109,14 @@ func (m *middleware) handle(c echo.Context) error {
 			e.Handled = true
 			e.Send()
 		}
+
+		if txEnded := tx.TransactionData == nil; txEnded {
+			return
+		}
 		tx.Result = apmhttp.StatusCodeResult(resp.Status)
 		if tx.Sampled() {
 			setContext(&tx.Context, req, resp, body)
 		}
-		body.Discard()
 	}()
 
 	handlerErr = m.handler(c)

module/apmechov4/middleware_test.go

@@ -165,6 +165,21 @@ func TestEchoMiddlewarePanic(t *testing.T) {
 	assertError(t, transport.Payloads(), "handlePanic", "boom", false)
 }
 
+func TestEchoMiddlewareEndedTxn(t *testing.T) {
+	tracer, _ := transporttest.NewRecorderTracer()
+	defer tracer.Close()
+
+	e := echo.New()
+	e.Use(apmecho.Middleware(apmecho.WithTracer(tracer)))
+	e.GET("/end-txn", handleEndTxn)
+
+	assert.NotPanics(t, func() {
+		w := doRequest(e, "GET", "http://server.testing/end-txn")
+		assert.Equal(t, http.StatusOK, w.Code)
+		tracer.Flush(nil)
+	})
+}
+
 func TestEchoMiddlewarePanicHeadersSent(t *testing.T) {
 	tracer, transport := transporttest.NewRecorderTracer()
 	defer tracer.Close()
@@ -218,6 +233,12 @@ func handlePanicAfterHeaders(c echo.Context) error {
 	panic("boom")
 }
 
+func handleEndTxn(c echo.Context) error {
+	txn := apm.TransactionFromContext(c.Request().Context())
+	txn.End()
+	return nil
+}
+
 func handleError(c echo.Context) error {
 	return errors.New("wot")
 }