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

scheduler/appengine/engine/engine.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 60 matching lines @@
 //    ErrNoOwnerPermission (assuming caller has READER access, else see above).
 type Engine interface {
         // GetVisibleJobs returns a list of all enabled scheduler jobs in no
         // particular order.
         GetVisibleJobs(c context.Context) ([]*Job, error)
 
         // GetVisibleProjectJobs returns a list of enabled scheduler jobs of some
         // project in no particular order.
         GetVisibleProjectJobs(c context.Context, projectID string) ([]*Job, error)
 
-        // GetVisibleJob returns single scheduler job given its full ID or nil if no such
-        // job or if not visible.
+        // GetVisibleJob returns single scheduler job given its full ID.
+        // ErrNoSuchJob error is returned if job doesn't exist OR isn't visible.
         GetVisibleJob(c context.Context, jobID string) (*Job, error)
 
         // ListVisibleInvocations returns invocations of a visible job, most recent first.
         // Returns fetched invocations and cursor string if there's more.
+        // error is ErrNoSuchJob if job doesn't exist or isn't visible.
         ListVisibleInvocations(c context.Context, jobID string, pageSize int, cursor string) ([]*Invocation, string, error)
 
         // GetVisibleInvocation returns single invocation of some job given its ID.
+        // ErrNoSuchInvocation is returned if either job or invocation doesn't exist
+        // or job and hence invocation isn't visible.
         GetVisibleInvocation(c context.Context, jobID string, invID int64) (*Invocation, error)
 
         // GetVisibleInvocationsByNonce returns a list of Invocations with given nonce.
         //
         // Invocation nonce is a random number that identifies an intent to start
         // an invocation. Normally one nonce corresponds to one Invocation entity,
         // but there can be more if job fails to start with a transient error.
         GetVisibleInvocationsByNonce(c context.Context, invNonce int64) ([]*Invocation, error)
 
         // PauseJob replaces job's schedule with "triggered", effectively preventing
@@ skipping 621 matching lines @@
         default:
                 return nil, transient.Tag.Apply(err)
         }
 }
 
 func (e *engineImpl) PublicAPI() Engine {
         return e
 }
 
 func (e *engineImpl) ListVisibleInvocations(c context.Context, jobID string, pageSize int, cursor string) ([]*Invocation, string, error) {
-        if job, err := e.GetVisibleJob(c, jobID); err != nil {
+        if _, err := e.GetVisibleJob(c, jobID); err != nil {
                 return nil, "", err
-        } else if job == nil {
-                // Either no Job or no access, both imply returning no invocations.
-                return nil, "", ErrNoSuchInvocation
         }
 
         if pageSize == 0 || pageSize > 500 {
                 pageSize = 500
         }
 
         // Deserialize the cursor.
         var cursorObj ds.Cursor
         if cursor != "" {
                 var err error
@@ skipping 1326 matching lines @@
                 }
                 if hasFinished {
                         return ctl.eng.rollSM(c, job, func(sm *StateMachine) error {
                                 sm.OnInvocationDone(saving.ID)
                                 return nil
                         })
                 }
                 return nil
         })
 }