Question

I have a program in C++ using winsock that connects to a server, the user’s will need to send data to this server periodically over a very long span of time(perhaps weeks without the need to reconnect).

I have found plenty of documentation on timeouts when establishing a connection, but I am trying to find out how long the connection lasts after it has been established. Does the connection last until either program is shut down? Can I connect then wait two hours to send something?

Answer 1

There’s no explicit connection lifetime limitation (at least in TCP). The connection lasts until one of the following:

• Either endpoint (application) shuts down (actually the connection may remain in half-duplex mode)
• Intermediate entity decides to terminate the connection (such as firewall, NAT or etc.)

In “real-world” internet connections are usually shut down forcibly after some period of time, especially if there’s no data sent. Besides of this, depending on the protocol, some servers refuse to keep the connection open for indefinite time (such as http servers).

In conclusion: there’s no generic way to discover the lifetime of the connection. You’re completely in the hands of the firewalls, proxies (if applicable), and the server behalf.

Sending some data periodically (such as keep-alive messages) usually help. It also helps to detect that the connection has been silently terminated.