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From "Oleg Kalnichevski (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HTTPCORE-242) NullPointerException in AsyncNHttpClientHandler when server sends reply before request is fully written.
Date Mon, 22 Nov 2010 13:23:13 GMT

    [ https://issues.apache.org/jira/browse/HTTPCORE-242?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12934457#action_12934457

Oleg Kalnichevski commented on HTTPCORE-242:

Hi Michael

Many thanks for the wire log! It helped a great deal.

Based on what I am seeing in the log, unfortunately, the behaviour of IIS/7.5 appears silly
and utterly illogical. The server responds early while the client is still busy writing out
the request body and nonetheless blissfully expects the client to keep the connection alive
somehow. The upshot of this silliness is that the client must either stop sending data and
switch to processing the response potentially leaving the connection in a inconsistent, non-reusable
state or continue writing request out under assumption that the server is still reading the
data (which begs the question what was the f..king point of sending the response early)

I see two possibilities to deal with the problem, none of which is ideal.

(1) If the server sends a response early, out of usual request/response sequence, the client
should stop writing out the request body, deal with the response, and then drop the connection
as non-reusable (which is basically the case). This, however, is very likely to interfere
with the NTLM authentication protocol, which is stateful by design and therefore cannot work
with non-persistent connections.

(2) Apply your patch and accept the risks of causing compatibility issues with those servers
that tend to respond early to POST requests but at least do not expect the client to keep
the connection alive.

My personal preference would be the first option given that the whole mess is a direct result
of IIS brokenness. In this case you will have to change your code to execute a GET request
for each new connection in order to force the NTLM authentication with the server. At any
rate it is massively more efficient to use an extra GET request for NTLM authentication instead
of a POST, which would require the same request body to be resent three times for no good

Do you think you could live with the first option?


> NullPointerException in AsyncNHttpClientHandler  when server sends reply before request
is fully written.
> ---------------------------------------------------------------------------------------------------------
>                 Key: HTTPCORE-242
>                 URL: https://issues.apache.org/jira/browse/HTTPCORE-242
>             Project: HttpComponents HttpCore
>          Issue Type: Bug
>          Components: HttpCore NIO
>    Affects Versions: 4.1
>         Environment: Server:  IIS/7.5 with NTLM authentication.
>            Reporter: Michael Poindexter
>         Attachments: httcore-quickresponse.pcap, HTTPCORE-242.patch, httpcore-connection-reuse-bug-fixed2.zip,
> I'm seeing a problem with AsyncNHttpClientHandler in v4.1 of HttpCore.  When I submit
a number of requests simultaneously or a single POST with a large body to a server using NTLM
authentication, 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)
> 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
> 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
>            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.

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