example/aws/request/httptrace: Fix example with timeouts and retries (#…

…3499)

The tracing example incorrectly copied the HTTP trace between retry
attempts, instead of replacing it. This update corrects this behavior so
that each request attempt has its own http trace. This also fixes
potential output of negative values.

example/aws/request/httptrace/main.go

@@ -55,7 +55,7 @@ func main() {
  for scanner.Scan() {
  trace, err := publishMessage(ctx, svc, topicARN, scanner.Text())
  if err != nil {
- fmt.Fprintf(os.Stderr, "failed to publish message, %v", err)
+ fmt.Fprintf(os.Stderr, "failed to publish message, %v\n", err)
  }
  log.Println(trace)
 
@@ -77,7 +77,7 @@ func publishMessage(ctx context.Context, svc *sns.SNS, topic, msg string) (*Requ
  Message: &msg,
  }, trace.TraceRequest)
  if err != nil {
- return nil, err
+ return trace, err
  }
 
  return trace, nil

example/aws/request/httptrace/trace.go

@@ -113,10 +113,15 @@ func (t *RequestTrace) TraceRequest(r *request.Request) {
  attempt.SignDone = time.Now()
  })
 
+ // Ensure that the http trace added to the request always uses the original
+ // context instead of each following attempt's context to prevent conflict
+ // with previous http traces used.
+ origContext := r.Context()
+
  // Send
  r.Handlers.Send.PushFront(func(rr *request.Request) {
  attempt.SendStart = time.Now()
- attempt.HTTPTrace = NewHTTPTrace(rr.Context())
+ attempt.HTTPTrace = NewHTTPTrace(origContext)
  rr.SetContext(attempt.HTTPTrace)
  })
  r.Handlers.Send.PushBack(func(rr *request.Request) {
@@ -398,7 +403,7 @@ func (t *HTTPTrace) wroteRequest(info httptrace.WroteRequestInfo) {
 }
 
 func safeTimeDelta(start, end time.Time) time.Duration {
- if start.IsZero() || end.IsZero() {
+ if start.IsZero() || end.IsZero() || start.After(end) {
  return 0
  }