FailFast(false), return helpful error message when context is time out

picker_wrapper.go

@@ -101,7 +101,15 @@ func doneChannelzWrapper(acw *acBalancerWrapper, done func(balancer.DoneInfo)) f
 // - the subConn returned by the current picker is not READY
 // When one of these situations happens, pick blocks until the picker gets updated.
 func (bp *pickerWrapper) pick(ctx context.Context, failfast bool, opts balancer.PickOptions) (transport.ClientTransport, func(balancer.DoneInfo), error) {
- var ch chan struct{}
+ var (
+ ch chan struct{}
+
+ // when the current picker returns balancer.ErrTransientFailure and failfast is false,
+ // this function will block until context is done.
+ // To return some helpful connection messages, like tls config error message,
+ // use pickErr to save balancer.ErrTransientFailure which occurred.
+ pickErr error
+ )
 
  for {
  bp.mu.Lock()
@@ -120,6 +128,14 @@ func (bp *pickerWrapper) pick(ctx context.Context, failfast bool, opts balancer.
  bp.mu.Unlock()
  select {
  case <-ctx.Done():
+ if pickErr != nil {
+ switch ctx.Err() {
+ case context.DeadlineExceeded:
+ return nil, nil, status.Errorf(codes.DeadlineExceeded, "latest connection error: %v", bp.connectionError())
+ case context.Canceled:
+ return nil, nil, status.Errorf(codes.Canceled, "latest connection error: %v", bp.connectionError())
+ }
+ }
  return nil, nil, ctx.Err()
  case <-ch:
  }
@@ -138,6 +154,7 @@ func (bp *pickerWrapper) pick(ctx context.Context, failfast bool, opts balancer.
  continue
  case balancer.ErrTransientFailure:
  if !failfast {
+ pickErr = err
  continue
  }
  return nil, nil, status.Errorf(codes.Unavailable, "%v, latest connection error: %v", err, bp.connectionError())