onClose event does not fire on connection lost

[micahbule]

Description

onClose event doesn't fire when a TCP client loses WiFi

Steps to reproduce

Steps to reproduce the behavior:

1. Instantiate a TCP Server on device1.
2. Instantiate a TCP Client on device2 and connect to device1.
3. Turn off WiFi for device2.

Current behavior

Client's socket in the TCP server is still connected.

Expected behavior

Client's socket in the TCP server must be disconnected.

Relevant information

OS	ubuntu 18.04
react-native	0.61.4
react-native-tcp-socket	3.3.1

[Rapsssito]

@micahbule, I am sorry, but TCP does not provide an explicit disconection event, since it is an idle protocol. You can find more information on this article about half-open connection:

TCP does have acknowledgments for data, so when one side sends data to the other side, it will receive an acknowledgment if the connection is stil active (or an error if it is not). Thus, broken connections can be detected by sending out data. It is important to note that the act of receiving data is completely passive in TCP; a socket that only reads cannot detect a dropped connection.

You will need to configure your communication protocol to detect a dropped connection. So, all you need to do is to try reading at some interval, and if the read fails, the connection has dropped.