[dashboard api] manage error when data in dashboard table is not valid json (#29999)

* retrieve dashboard api

* Apply suggestions from code review

Co-authored-by: Arve Knudsen <arve.knudsen@gmail.com>

* Update pkg/api/dashboard.go

Co-authored-by: Arve Knudsen <arve.knudsen@gmail.com>

Co-authored-by: Arve Knudsen <arve.knudsen@gmail.com>

pkg/api/dashboard.go

@@ -54,6 +54,20 @@ func (hs *HTTPServer) GetDashboard(c *models.ReqContext) Response {
 		return rsp
 	}
 
+	// When dash contains only keys id, uid that means dashboard data is not valid and json decode failed.
+	if dash.Data != nil {
+		isEmptyData := true
+		for k := range dash.Data.MustMap() {
+			if k != "id" && k != "uid" {
+				isEmptyData = false
+				break
+			}
+		}
+		if isEmptyData {
+			return Error(500, "Error while loading dashboard, dashboard data is invalid", nil)
+		}
+	}
+
 	guardian := guardian.New(dash.Id, c.OrgId, c.SignedInUser)
 	if canView, err := guardian.CanView(); err != nil || !canView {
 		return dashboardGuardianResponse(err)

pkg/api/dashboard_test.go

@@ -1009,7 +1009,9 @@ func TestDashboardAPIEndpoint(t *testing.T) {
 				return nil
 			})
 			bus.AddHandler("test", func(query *models.GetDashboardQuery) error {
-				query.Result = &models.Dashboard{Id: 1, Data: &simplejson.Json{}}
+				dataValue, err := simplejson.NewJson([]byte(`{"id": 1, "editable": true, "style": "dark"}`))
+				require.NoError(t, err)
+				query.Result = &models.Dashboard{Id: 1, Data: dataValue}
 				return nil
 			})