Peter Soles wrote:
I'm using HttpCore NIO as part of a web app that issues long polls to a
remote server on behalf of clients - basically it is a proxy. I
previously used NIO as part of a simulator I was building over the
summer and had good success with it! Now I am trying to use an enhanced
version of the code as part of my web app since it is possible that my
webapp may have to open many long polls to the remote server. One of
the enhancements is I added to my code is connection recycling.
My webapp operates as expected in my development environment under
Windows and I am able to make long polls using recycled connections
without errors. However, when I deploy it to a server running on Linux
I get frequent fatalIOExceptions raised by the EventListener. I traced
this to my connection recycler object that attempts to re-use a
connection. It appears that the code sometimes hangs when I issue
NHttpConnection.requestOutput() on a recycled connection, and then the
code throws the IOException: Connection reset by peer.
I use tcpdump to monitor the outgoing messages from my webapp to the
remote server and I observe that the message I am trying to send when I
call requestOutput() is never sent over the wire so I suspect that the
"connection reset by peer" is not really what is happening. I actually
suspect/hope that I am doing something obviously wrong in my recycle
connection code that is causing this to happen.
I've attached my code that implements my NIO communication stage for my
web app. To use, you create a new HttpClientNIO object and then you can
send a non-blocking request using HttpClientNIO.sendRequest(request,
callback). When the request completes you will receive notification
through the callback.
My connection logic is this:
1. When request arrives, check for available connection on queue.
2. If there is not an available connection:
a) call DefaultConnectionIOReactor.connect() start creation of new
connection
b) use connection as described in documentation
c) when HttpRequestExecutionHandler.handleResponse() has completed
it's processing, put connection on queue for re-use.
3. If there is an available connection
a) make sure connection is active
b) get the HttpContext from the connection NHttpConnection.getContext()
c) reset values as needed
d) call NHttpConnection.requestOutput
Am I missing something? I should also say that I generally instantiate
an SSLClientIOEventDispatch since the remote server uses SSL but I also
get fatalIOException when I am not using SSL.
Peter
Peter,
It all sounds very reasonable. I have a question, though. When you put
persistent connections on the re-use queue, do you clear interest in
read event notifications? This might explain why the I/O event dispatch
does not get called when a connection is closed by the peer on the
opposite end.
Anyways, for what it is worth to you, I have also put together a very
experimental and very buggy prototype of an async HTTP agent based on
HttpCore NIO and HttpClient 4.0. Feel free to take a look at my
implementation of the non-blocking connection manager and pick some
ideas or bits of code:
http://svn.apache.org/repos/asf/httpcomponents/asynchttpclient/trunk/
This is how this API looks in action:
http://svn.apache.org/repos/asf/httpcomponents/asynchttpclient/trunk/src/examples/org/apache/http/examples/nio/client/AsyncClientRequest.java
You may take a special look at the code that adds logging capability to
some of the HttpCore NIO classes.
http://svn.apache.org/repos/asf/httpcomponents/asynchttpclient/trunk/src/main/java/org/apache/http/impl/nio/conn/LoggingNHttpClientConnection.java
http://svn.apache.org/repos/asf/httpcomponents/asynchttpclient/trunk/src/main/java/org/apache/http/impl/nio/conn/LoggingIOSession.java
This really helps with debugging.
Hope this helps somewhat.
Oleg
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