Java NIO: What does IOException: Broken pipe mean? [duplicate]

What causes a "broken pipe", and more importantly, is it possible to recover from that state?

It is caused by something causing the connection to close. (It is not your application that closed the connection: that would have resulted in a different exception.)

It is not possible to recover the connection. You need to open a new one.

If it cannot be recovered, it seems this would be a good sign that an irreversible problem has occurred and that I should simply close this socket connection. Is that a reasonable assumption?

Yes it is. Once you've received that exception, the socket won't ever work again. Closing it is is the only sensible thing to do.

Is there ever a time when this IOException would occur while the socket connection is still being properly connected in the first place (rather than a working connection that failed at some point)?

No. (Or at least, not without subverting proper behavior of the OS'es network stack, the JVM and/or your application.)

Is it wise to always call SocketChannel.isConnected() before attempting a SocketChannel.write() ...

In general, it is a bad idea to call r.isXYZ() before some call that uses the (external) resource r. There is a small chance that the state of the resource will change between the two calls. It is a better idea to do the action, catch the IOException (or whatever) resulting from the failed action and take whatever remedial action is required.

In this particular case, calling isConnected() is pointless. The method is defined to return true if the socket was connected at some point in the past. It does not tell you if the connection is still live. The only way to determine if the connection is still alive is to attempt to use it; e.g. do a read or write.

Broken pipe simply means that the connection has failed. It is reasonable to assume that this is unrecoverable, and to then perform any required cleanup actions (closing connections, etc). I don't believe that you would ever see this simply due to the connection not yet being complete.

If you are using non-blocking mode then the SocketChannel.connect method will return false, and you will need to use the isConnectionPending and finishConnect methods to insure that the connection is complete. I would generally code based upon the expectation that things will work, and then catch exceptions to detect failure, rather than relying on frequent calls to "isConnected".

Broken pipe means you wrote to a connection that is already closed by the other end.

isConnected() does not detect this condition. Only a write does.

is it wise to always call SocketChannel.isConnected() before attempting a SocketChannel.write()

It is pointless. The socket itself is connected. You connected it. What may not be connected is the connection itself, and you can only determine that by trying it.