scheduler ACLs: improve ACL-related error handling in UI and API.

scheduler/appengine/ui/invocation.go

 // Copyright 2015 The LUCI Authors.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //      http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
@@ skipping 38 matching lines @@
         }()
         wg.Add(1)
         go func() {
                 defer wg.Done()
                 job, err2 = eng.GetVisibleJob(c.Context, projectID+"/"+jobName)
         }()
         wg.Wait()
 
         // panic on internal datastore errors to trigger HTTP 500.
         switch {
+        case err2 == engine.ErrNoSuchJob:
+                http.Error(c.Writer, "No such job or no permission", http.StatusNotFound)
+                return
+        case err1 == engine.ErrNoSuchInvocation:
+                http.Error(c.Writer, "No such invocation", http.StatusNotFound)
+                return
         case err1 != nil:
                 panic(err1)
         case err2 != nil:
                 panic(err2)
-        case inv == nil:
-                http.Error(c.Writer, "No such invocation", http.StatusNotFound)
-                return
-        case job == nil:
-                http.Error(c.Writer, "No such job", http.StatusNotFound)
-                return
         }
 
         jobUI := makeJob(c.Context, job)
         templates.MustRender(c.Context, c.Writer, "pages/invocation.html", map[string]interface{}{
                 "Job": jobUI,
                 "Inv": makeInvocation(jobUI, inv),
         })
 }
 
 ////////////////////////////////////////////////////////////////////////////////
@@ skipping 17 matching lines @@
         switch err := cb(projectID+"/"+jobName, invIDAsInt); {
         case err == engine.ErrNoOwnerPermission:
                 http.Error(c.Writer, "Forbidden", 403)
                 return
         case err != nil:
                 panic(err)
         default:
                 http.Redirect(c.Writer, c.Request, fmt.Sprintf("/jobs/%s/%s/%s", projectID, jobName, invID), http.StatusFound)
         }
 }