app2.go

// stream is *Stream and err is error
// err filled if we fail to listen for events 
stream, err := observable3.Execute(serviceID, "send")
if err != nil {
  log.Fatal(err)
}

for {
  select {
  case execution := <- stream.Executions:
    // exection.Err is an error
    // filled when task execution failed
    if exection.Err != nil {
        continue
    }

    fmt.Println(execution.ID)
    
    // err is an error
    // send on stream error
    // if received, stream.Executions channel will be closed too.
    case err := <- stream.Err:
    
  }
}

stream.Close()