SocketProgramming

Given a TCP client/server model where the client and server are running in two different systems and a proxy is in between them, assume the client is able to send messages to the server through the proxy, then the server suddenly becomes non-responsive (say it got reset). What happens to the connection between the proxy and server

Either:

1. Nothing.
2. A read timeout, or
3. a 'connection reset' error

depending entirely on what the proxy is doing. If it's receiving, (2), or (3) if there was already a pending send. If it's sending, (3), but not on the first send, because of buffering. Eventually a send will cause (3).

and how to handle this?

Close the connection, and the connection to the client. If it was a reset, you might want to propagate that to the client via a technique I will not document here as it is so widely misused. If it was a read timeout, you might even want to try to propagate that to the client by simply doing nothing for five minutes or whatever is appropriate, and then closing or resetting the connection.

I mean, what technique can I employ to detect such an event, close my connection, and return an error message to the client?

See above.

One way I can think of is to check the receive buffer in the proxy, and if there is no data in it for some time, tell the client that the server is down. But I think that timeout is a primitive approach.

It isn't.

Are there any known standard methods or alternatives available in socket programming for this?

See above.