[FIXED] Jetty how to detect if HTTP connection was closed by client

Issue

Problem

Jetty 9 based server is processing time consuming (30-60 sec) and computation heavy (~20 threads involved in parallel processing) requests.

Due to interactive nature, client may cancel HTTP request after few seconds and send a new one.

It is desirable to cancel computation immediately if connection has been closed by client.

Unsuccessful attempts

1. In case of closed HTTP connection, attempt to write to response output stream would trigger IOException. Though, in case of this application, HTTP status depends on result of whole computation so it is not possible to write anything back to socket in the middle of processing. Thus, this option is not applicable.

2. Jetty have handy HttpConnection.getCurrentConnection() method which can be used to get references to some internal classes related to HTTP connection including underlying SocketChannel. Though I haven't found a way to check liveliness of connection though SocketChannel or other Jetty's classes related to connection.

Solution

The best choice is to use the javax.servlet.AsyncContext and its javax.servlet.AsyncListener.

Start with a call to java.servlet.HttpServletRequest.startAsync() to get the AsyncContext.

Then add a custom AsyncListener of your own, don't forget to also set a timeout on your AsyncContext (as its existence overrides the default Idle Timeout mechanism)

You'll get events that mean something useful to you ...

• onComplete - the processing has completed
• onError - the processing has failed (such as a unexpected connection termination)
• onTimeout - the AsyncContext timeout has fired

This is the mechanism that the Servlet API has provided for exactly your situation: computation or backend heavy processing during an active request that might be terminated early.

Answered By - Joakim Erdfelt