Return an error for a canceled request.

Allow the datasource to decide how to handle a
canceled request.

public/app/core/services/backend_srv.js

@@ -120,21 +120,15 @@ function (angular, _, coreModule, config) {
 
       return $http(options).then(null, function(err) {
         if (err.status === HTTP_REQUEST_ABORTED) {
-          // Need to return the right data structure so it has no effect on
-          // iterating over returned data in datasource.ts#115
-          // TODO: Hitting another refresh cancels the "loading" animation on
-          // panes. Figure out how to keep it going.
-          return {
-            data: {
-              data: {
-                result: []
-              }
-            }
-          };
+          // TODO: Hitting refresh before the original request returns cancels
+          // the "loading" animation on the panes, but it should continue to be
+          // visible.
+          err.statusText = "request aborted";
+          return err;
         }
 
         // handle unauthorized for backend requests
-        if (requestIsLocal && firstAttempt  && err.status === 401) {
+        if (requestIsLocal && firstAttempt && err.status === 401) {
           return self.loginPing().then(function() {
             options.retry = 1;
             canceler.resolve();

public/app/plugins/datasource/prometheus/datasource.ts

@@ -58,6 +58,7 @@ export function PrometheusDatasource(instanceSettings, $q, backendSrv, templateS
     return escapedValues.join('|');
   };
 
+  var HTTP_REQUEST_ABORTED = -1;
   // Called once per panel (graph)
   this.query = function(options) {
     var self = this;
@@ -107,6 +108,9 @@ export function PrometheusDatasource(instanceSettings, $q, backendSrv, templateS
       var result = [];
 
       _.each(allResponse, function(response, index) {
+        if (response.status === HTTP_REQUEST_ABORTED) {
+          return;
+        }
         if (response.status === 'error') {
           self.lastErrors.query = response.error;
           throw response.error;