What will happen when the server receives a message for a user who has gone offline? If the receiver has disconnected, the server can notify the sender about the delivery failure. However, if it is a temporary disconnect, e.g., the receiver’s long-poll request just timed out, then we should expect a reconnect from the user. In that case, we can ask the sender to retry sending the message. This retry could be embedded in the client’s logic so that users don’t have to retype the message. The server can also store the message for a while and retry sending it once the receiver reconnects.
why is it a failure if the receiver has disconnected? why don’t we store the message and give it to the user when he comes back online?