Re: HTTP communication

[Maxim Neshcheret <Ma...@cma.ru>]

Hi André,

First about network. Client and server are in the same segment and there
are no firewalls in between them.
Second I expect connection to be alive because during initiation I specify
'keep-alive' property of HTTP request. Also
Tomcat and WLS are configured to support keepalive connections.

From what I noticed, I monitored TCP connection using TCPView and
Wireshark (on the client side), TCP connection is still alive
even Tomcat or WLS cannot write to the socket.

Just to mention, I have in my code an option to send periodical heartbeats
to the client if there is no data. It is configurable and
when I use this option everything works fine. But if I don’t send
heartbeats as I wrote before connection becomes stale and I want
to understand why it happens so that I can initiate, for example,
automatic client logoff and cleanup resources.



On 29/01/16 11:33, "André Warnier (tomcat)" <aw...@ice-sa.com> wrote:

>On 28.01.2016 18:38, Maxim Neshcheret wrote:
>> I have a problem with my java application related to HTTP communication.
>>
>> Application description:
>>
>> 1.      Client – server. Server is running in servlet container. We use
>>Tomcat.
>>
>> Client use java HTTP library to communicate with the server.
>>
>> 2.      When client establish connection to the server it sends GET
>>request (keepalive) and server creates AsyncContext for the client with
>>10 days timeout.
>>
>> 3.      After connection established server periodically sends data to
>>the client using AsyncContext and on the client side there is special
>>thread which reads and processes the data.
>>
>[ snip ...]
>>
>> Usually this code works fine but it there is no data from server to
>>client for 1 day and after 24 hours (can be 16 or 12) data appears,
>>server cannot send data to the client.
>> In the log there is no error. It is written that everything flushed but
>>client still waiting for data in “final String line = reader.readLine();”
>> When 2nd portion of data is sent by the server, then during flush I see
>>the following error
>>
>> 2016-01-26 00:00:00,051|INFO |GWNotify-2/50       |ClientAbort
>> 2016-01-26 00:00:00,051|TRACE|GWNotify-2/50
>>|ClientAbortException:java.io.IOException: APR error: -32
>> org.apache.catalina.connector.ClientAbortException:
>>java.io.IOException: APR error: -32
>[snip ...]
>
>Hi.
>I am unqualified to check your code, but a first question would be :
>where is the Client,
>and where is the Server and what is the connection between them like ?
>
>And the reason for the question is : it is not at all unusual, that any
>kind of network 
>connection would be interrupted at some point over a 24-hour period,
>specially if nothing
>is sent over that connection for a long time.
>When a connection "disappears", TCP sends no signal to either the client
>or the server, 
>and an error will only be caught, if one of the parties tries to write to
>the (now gone) 
>connection (which seems to be what happens above, when the server tries
>to write to the 
>Client, and gets a "client is no longer there" exception).
>
>If you want to avoid this, you will have to handle this in your code.
>You cannot just 
>expect the connection to be alive no matter what.
>
>
>
>
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