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From André Warnier>
Subject Re: Request Timeout and empty post data issue
Date Thu, 26 Dec 2013 23:11:42 GMT
Peter Rifel wrote:
>> -----Original Message-----
>> From: Konstantin Preißer []
>> Sent: Thursday, December 26, 2013 1:28 PM
>> To: 'Tomcat Users List'
>> Subject: RE: Request Timeout and empty post data issue
>> Hi,
>>> -----Original Message-----
>>> From: Peter Rifel []
>>> Sent: Thursday, December 26, 2013 9:45 PM
>>> To:
>>> Subject: Request Timeout and empty post data issue
>>> Hello,
>>> I'm currently running Tomcat 7.0.42 on Ubuntu 12.04 with OpenJDK 1.7.0_25.
>>> I'm using Apache Tomcat Native library 1.1.27 with APR version 1.4.6.
>>> I'm noticing in my access logs that some of our POST requests don't have any
>>> POST data and all have response times of a few ms over 20000ms.  I'm trying
>>> to figure out whether this issue is client side or server side.  The response
>>> code and response size for these requests are normal.  Can anyone tell me
>>> under what circumstances this would happen?  I noticed that our connector's
>>> connectionTimeout is set to 20000ms, but it wouldn't make sense for that
>>> value to be a part of this issue because a connection timeout only occurs
>>> when the URI hasn't been received by tomcat in that amount of time, which
>>> is clearly not happening here (I was able to confirm this with telnet; a
>>> connection timeout will not write anything to the access logs).
>>> The "request" is making it to my servlet (logging confirms this) but for some
>>> reason tomcat doesn't see any request parameters and all of the response
>>> times in our access logs are just above 20 seconds.  Does this mean that my
>>> servlet is taking 20 seconds to process the request?  Is there some other
>>> timeout value somewhere that defaults to 20 seconds?  Is there a way for
>>> me to see exactly what is taking so long?  Its incredibly hard to debug this
>>> because we cant reproduce this bug on our own without any post data and
>>> <1% of our production traffic is having this issue.  To try and gather more
>>> on this, I added a servlet filter that logs all of our POST request parameters
>>> the access log and I can confirm that there are no parameters on these
>>> specific requests.
>>> The lack of post data makes me think its a client issue, but that doesn't
>>> explain why all of these requests take ~20 seconds to be processed.
>>> I'd appreciate any ideas on what could cause this.
>> Did you try to set the "connectionTimeout" to some other value to see if the requests
still take ~ 20s?
>> I just tested with Tomcat 7.0.47 and HTTP APR connector, and for me the "connectionTimeout"
value is also applied when reading the POST data: When the client does not send a byte in
this interval (20s), then this will trigger some timeout error.
>> E.g., if you send the following POST request without a body (2x CR LF after the last
>> POST /MyWebapp/PostServlet HTTP/1.1
>> Host: localhost
>> Connection: keep-alive
>> Content-Length: 999
>> Content-Type: application/x-www-form-urlencoded
>> Then after the connectionTimeout interval, an occurs
at (e.g. when you directly read the Request
input stream), so that Tomcat doesn't wait forever for further data when the client is already
gone. Note that the exception did not occur when I called  request.getParameter("xxx") - it
just returned null.
>> It could be possible that a client sends a request with complete headers, but when
sending the POST body the client waits too long so that Tomcat applies the connectionTimeout
before the full request body is received. The request will then be logged as the request headers
where completely received.
>> Regards,
>> Konstantin Preißer
> Konstantin,
> I changed the connectionTimeout and that value is being reflected in our access logs.
 So this means that tomcat is not receiving a body with the POST request, indicating a client-side
or network problem? 

It could also of course be a malicious client, doing this just to bother you.
(a form of DoS attack).

We never read the input stream directly, we only use getParameter so that would explain 
why our servlet isn't throwing a SocketTimeoutException.

Calling getParameters(), as far as I know, forces Tomcat to read the /whole/ request body,

to parse the parameters before returning from getParameters().

That is why I was a bit curious about how you managed to determine, in the servlet filter,

that there were no parameters.
Somehow it seems to me that there is still an unexplained phenomenon there, as follows :

Suppose that there is supposed to be a body with parameters, the total length of that body

being given by the Content-length header.
Your code calls getParameters() for the first time.  The underlying Tomcat code reads the

Either this body can be read completely (up to Content-length) and parsed into parameters,

and the getParameter() call returns.
Or else, the read of the POST body blocks for lack of data, before Content-length has been

reached.  In that case, the call to getParameter() should not return. And if that 
situation lasts long enough, a time-out should occur and some exception should be thrown.

So, unless I am missing something (which is very possible, as I did not consult the 
underlying code), the only way that the servlet filter could determine that there are no 
parameters, would be if there was no body (Content-length = 0).  Otherwise, it would be 
faced with the timeout before the return from getParameters(), no ?

   It would be nice if the connectionTimeout documentation could mention this scenario as

> Thank you for your quick response!
> Peter
> Peter
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