What are some common SocketExceptions and what is causing them?

Question

I've been caught catching SocketExceptions belonging to subspecies like for example Broken pipe or Connection reset. The question is what to do with the slippery bastards once they're caught.

Which ones may I happily ignore and which need further attention? I'm looking for a list of different SocketExceptions and their causes.

Answer 1

In terms of Java web development, a Broken pipe or a Connection reset basically means that the other side has closed the connection. This can under each be caused by the client pressing Esc while the request is still running or navigating away by link/bookmark/addressbar while the request is still running. You see this particular error often in long running requests such as large file downloads and unnecessarily large/slow business tasks (which is not good for the impatient user, about 3 secs is really the max). In rare cases it can also be caused by a hardware/network problem, such as a network outage at either server or client side.

This exception can be thrown when a flush() or close() on the outputstream of the response is invoked. You as server side cannot do anything against it. You cannot recover from it as you cannot (re)connect the client due to security restrictions in HTTP. In most cases you also shouldn't even try to, because this is often client's own decision. Just ignore it or log it for pure statistics.

Answer 2

One of the other causes is usually the TCP/IP stack settings on the Operating System. Haven't tried it on Linux yet but one platform i've worked on is Sun's Solaris 9/10 Operating System. The basic idea is that Solaris has a tunable TCP/IP stack which you can tune while running your web applications.

So there are two parameters that you should be aware of

• *tcp_conn_req_max_q0* - queue of incomplete handshakes
• *tcp_conn_req_max_q1* - queue of complete handshakes
• *tcp_keepalive_interval* - keepalive
• *tcp_time_wait_interval* - time of a TCP segment that's considered alive in the internet

All the above parameters affect how much load can the system take (from a TCP/IP perspective) and on the flipside affects the occurrence of certain types of SocketExceptions - such as the ones BalusC pointed above.

This is obviously quite convoluted but the point i'm trying to make is that the OS you're hosting your apps on more often than not, offers you mitigation strategies.