Messages doesn't come if I lost my connection in socket.io - node.js

Question

I am building chat app.My server code:
socket.on('sendMessage',function(data){
var to=data.To;
var from=data.From;
var message=data.Message;
var sendData={
to:to,
from:from,
message:message,
messageId:randomId
}
io.to(to).emit("processmessage",sendData);
});
It is working well when receiver is online.But when I plugged out the ethernet cable and when someone sends a message to me the message doesn't come after I reconnected. (I am reconnecting within 10 seconds.)
Ps:After I reconnected new messages are coming without any problem.I lost the messages when I reconnecting.
How can I resolve this ?

Answer 1

You can implement a retry system that uses each messages unique id and timestamp to check whether it has reached the other side.
You would require that the receiver send back an acknowledgement that it has received a message of a particular ID.
Set a timeout (T) where you will retry a message after (T) seconds if it hasn't been acknowledged.
You can keep a buffer of messages that you send, then for every message that you confirm has been received (via an acknowledgement from the receiver), you can remove it from the buffer. After receiving an acknowledgement, you can also check the oldest message in your buffer to see if it is older than (T). If it is, you can retry the message and reset the timestamp. Continue checking the next oldest until you find one that is not older than (T). Then move on to sending next message.
This procedure will help your system recover messages that may have not made it to the receiver during downtime in the network.