Socket read fails but write is successful. Why?

Question

Hi once more!
I have a Java application, reading and writing from/to a client socket:
InputStream is = socket.getInputStream();
BufferedReader br = new BufferedReader(new InputStreamReader(is));
i = br.read();
...If i is equal to -1, it means there's no connection or that somehow the connection is unavailable right? So, how come is it possible to write to the socket's output stream with success after that read( ) returning -1? Shouldn't it also fail?
I'm trying a "persistent" TCP connection, so I use that condition (read () == -1) to determine when the connection is down (read() is only blocking a certain amount of time).
Thanks!

Answer 1

I suggest you to have a process constantly
sending a byte just to check that you still have
the ability to send a packetNow you've got it.That's what I'm doing, yet I feel in my case it's not enough.
I communicate with the server asynchronously. I send packets.. somewhen the server sends packets to my client.
This way, I have to be continuously reading from the socket's Input Stream, in order to check for incoming packets (which may arrive at any time)... Thus, I have to be sure I can read from the socket..
As the connection may timeout (if neither my client nor the server write anything to the socket) I send a dummy packet once per minute.
However:
1) This is too long to check connection status (only 1 time each minute)
2) It doesn't tell me I can read ok from the socket - check the case where I could write but read ( ) returned -1. This is abnormal behaviour in my case.. do you think if the server was sending some packets, my read ( ) would be able to capture them (even after returning -1 for quite a while)? It seemed to me I was able to send, yet unable to receive.. or my packets weren't actually reaching the server even though they seemed to be.
What write does is cause packets to be sent which
require acknowledgement, and if the ACKs don't
arrive, eventually a subsequent write() will fail. A
read doesn't engage in any wire protocol at all,
which is why it can't be used to detect a connection
failure other than via a read timeout, or as a result
of prior writes.Why does write ( ) doesn't fail when I unplug the cable? Either way this situation isn't quite important, as long as my packets start actually reaching the server after the cable is plugged back in. Curious, however, how write ( ) doesn't fail..