func roundTrip(conn *client.Conn, deviceId, channelId, endpoint string, version int64) (err error) {
stopChan, errChan := make(chan bool), make(chan error)
defer close(stopChan)
go func() {
err := client.Notify(endpoint, version)
if err != nil {
err = fmt.Errorf("Error sending update %d on channel %q: %s",
version, channelId, err)
}
select {
case <-stopChan:
case errChan <- err:
}
}()
go func() {
var (
pendingAccepts []client.Update
err error
)
timeout := time.After(15 * time.Second)
for ok := true; ok; {
var packet client.Packet
select {
case ok = <-stopChan:
case <-timeout:
ok = false
err = client.ErrTimedOut
case packet, ok = <-conn.Packets:
if !ok {
err = client.ErrChanClosed
break
}
updates, _ := packet.(client.ServerUpdates)
if len(updates) == 0 {
continue
}
pendingAccepts = append(pendingAccepts, updates...)
var (
update client.Update
hasUpdate bool
)
for _, update = range updates {
if update.ChannelId == channelId && update.Version >= version {
hasUpdate = true
break
}
}
if !hasUpdate {
continue
}
ok = false
if update.Version != version {
err = fmt.Errorf("Wrong update version: got %d; want %d",
update.Version, version)
break
}
}
}
if acceptErr := conn.AcceptBatch(pendingAccepts); acceptErr != nil {
err = fmt.Errorf("Error acknowledging updates: %s", acceptErr)
}
select {
case <-stopChan:
case errChan <- err:
}
}()
for i := 0; i < 2; i++ {
if err := <-errChan; err != nil {
return err
}
}
return nil
}
