rc: add Job to ctx so it can be used elsewhere

See: https://forum.rclone.org/t/uploads-start-repeatedly-failing-after-a-while-using-rc-sync-copy-vs-rclone-copy-for-dropbox/38873/

fs/rc/jobs/job.go

@@ -83,6 +83,17 @@ func (job *Job) removeListener(fn *func()) {
 	}
 }
 
+// OnFinish adds listener to job that will be triggered when job is finished.
+// It returns a function to cancel listening.
+func (job *Job) OnFinish(fn func()) func() {
+	if job.Finished {
+		fn()
+	} else {
+		job.addListener(&fn)
+	}
+	return func() { job.removeListener(&fn) }
+}
+
 // run the job until completion writing the return status
 func (job *Job) run(ctx context.Context, fn rc.Func, in rc.Params) {
 	defer func() {
@@ -237,6 +248,11 @@ func getFilter(ctx context.Context, in rc.Params) (context.Context, error) {
 	return ctx, nil
 }
 
+type jobKeyType struct{}
+
+// Key for adding jobs to ctx
+var jobKey = jobKeyType{}
+
 // NewJob creates a Job and executes it, possibly in the background if _async is set
 func (jobs *Jobs) NewJob(ctx context.Context, fn rc.Func, in rc.Params) (job *Job, out rc.Params, err error) {
 	id := atomic.AddInt64(&jobID, 1)
@@ -274,9 +290,14 @@ func (jobs *Jobs) NewJob(ctx context.Context, fn rc.Func, in rc.Params) (job *Jo
 		StartTime: time.Now(),
 		Stop:      stop,
 	}
+
 	jobs.mu.Lock()
 	jobs.jobs[job.ID] = job
 	jobs.mu.Unlock()
+
+	// Add the job to the context
+	ctx = context.WithValue(ctx, jobKey, job)
+
 	if isAsync {
 		go job.run(ctx, fn, in)
 		out = make(rc.Params)
@@ -303,12 +324,22 @@ func OnFinish(jobID int64, fn func()) (func(), error) {
 	if job == nil {
 		return func() {}, errors.New("job not found")
 	}
-	if job.Finished {
-		fn()
-	} else {
-		job.addListener(&fn)
+	return job.OnFinish(fn), nil
+}
+
+// GetJob gets the Job from the context if possible
+func GetJob(ctx context.Context) (job *Job, ok bool) {
+	job, ok = ctx.Value(jobKey).(*Job)
+	return job, ok
+}
+
+// GetJobID gets the Job from the context if possible
+func GetJobID(ctx context.Context) (jobID int64, ok bool) {
+	job, ok := GetJob(ctx)
+	if !ok {
+		return -1, ok
 	}
-	return func() { job.removeListener(&fn) }, nil
+	return job.ID, true
 }
 
 func init() {

fs/rc/jobs/job_test.go

@@ -44,13 +44,22 @@ func TestJobsExpire(t *testing.T) {
 	jobs := newJobs()
 	jobs.opt.JobExpireInterval = time.Millisecond
 	assert.Equal(t, false, jobs.expireRunning)
+	var gotJobID int64
+	var gotJob *Job
 	job, out, err := jobs.NewJob(ctx, func(ctx context.Context, in rc.Params) (rc.Params, error) {
 		defer close(wait)
+		var ok bool
+		gotJobID, ok = GetJobID(ctx)
+		assert.True(t, ok)
+		gotJob, ok = GetJob(ctx)
+		assert.True(t, ok)
 		return in, nil
 	}, rc.Params{"_async": true})
 	require.NoError(t, err)
 	assert.Equal(t, 1, len(out))
 	<-wait
+	assert.Equal(t, job.ID, gotJobID, "check can get JobID from ctx")
+	assert.Equal(t, job, gotJob, "check can get Job from ctx")
 	assert.Equal(t, 1, len(jobs.jobs))
 	jobs.Expire()
 	assert.Equal(t, 1, len(jobs.jobs))