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From Michael Poindexter <mpoindex...@qumu.com>
Subject Possible Bug With HttpCore-NIO 4.1
Date Sat, 20 Nov 2010 03:48:17 GMT
I'm seeing a problem with AsyncNHttpClientHandler in v4.1 of HttpCore.  When I submit a number
of requests simultaneously (anything > 12 seems to trigger it for me), I get this exception:

Caused by: java.lang.NullPointerException
at org.apache.http.nio.protocol.AsyncNHttpClientHandler.outputReady(AsyncNHttpClientHandler.java:268)
at org.apache.http.nio.protocol.BufferingHttpClientHandler.outputReady(BufferingHttpClientHandler.java:118)
at org.apache.http.impl.nio.DefaultNHttpClientConnection.produceOutput(DefaultNHttpClientConnection.java:207)
at org.apache.http.impl.nio.ssl.SSLClientIOEventDispatch.outputReady(SSLClientIOEventDispatch.java:245)
at com.qumu.cxf.rt.transport.ahttp.MultiProtocolIOEventDispatch.outputReady(MultiProtocolIOEventDispatch.java:49)
at org.apache.http.impl.nio.reactor.BaseIOReactor.writable(BaseIOReactor.java:185)
at org.apache.http.impl.nio.reactor.AbstractIOReactor.processEvent(AbstractIOReactor.java:338)
at org.apache.http.impl.nio.reactor.AbstractIOReactor.processEvents(AbstractIOReactor.java:315)
at org.apache.http.impl.nio.reactor.AbstractIOReactor.execute(AbstractIOReactor.java:275)
at org.apache.http.impl.nio.reactor.BaseIOReactor.execute(BaseIOReactor.java:104)
at org.apache.http.impl.nio.reactor.AbstractMultiworkerIOReactor$Worker.run(AbstractMultiworkerIOReactor.java:542)
at java.lang.Thread.run(Thread.java:680)

Some details about my code/environment:  Each request is submitted on it's own connection.
 The requests are all POSTs.  I am using SSL, and I cannot seem to reproduce this over plain
HTTP.  The server I am connecting to is IIS/7.5.  I am using NTLM authentication (with JCIFS),
so I need to keep the connection alive through several round trips as the NTLM message exchange
occurs.

I dug into the HttpCore code, and here is my analysis of what is occurring:
1.) AsyncNHttpClientHandler.connect calls requestReady to send the initial request.  This
sets the request on the connection, and the connection starts writing the request line in
response to write events.
2.) The server receives the request line and responds immediately with a 401 Unauthorized.
 At this point the POST body has not been fully sent to the server.
3.) AsyncNHttpClientHandler.inputReady is called with the response from the server.  At this
point processResponse is called, and my code executes.  I detect that the request needs authentication
and I need to retransmit my request with an auth header, so my ConnectionReuseStrategy says
to keep the connection alive.
4.) When control returns from my code, the code in processResponse calls connState.resetOutput,
clearing the entity and request in connState.  There is still output from the POST body pending.
5.)  processResponse calls conn.requestOutput to reenable write events since the connection
is not to be closed.
6.)  A write event happens, and DefaultNHttpClientConnection.produceOutput is called.  Since
the output from the initial request never finished, contentEncoder is not null and so AsyncNHttpClientHandler.outputReady
is called instead of requestReady.  Since connState was reset, the entity is null and this
NPE happens.

I copied the code of AsyncNHttpClientHandler and added a conn.suspendInput() call in requestReady:
            if (entityReq != null && entityReq.expectContinue()) {
                .....
            } else {
            conn.suspendInput();
            }
and a conn.requestInput call in outputReady:
            entity.produceContent(encoder, conn);
            if(encoder.isCompleted()) {
            conn.requestInput();
            }
and this seemed to resolve the issue by not allowing the request and response to overlap,
but I'm not sure this is the best way to fix it.

Is my analysis correct?  If so, is there a better way to fix this?

Mike Poindexter


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