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From "Claus Ibsen (JIRA)" <>
Subject [jira] Commented: (CAMEL-1461) A request route with a topic node incurs a 20 second wait and refers to the wrong MEP.
Date Sat, 04 Apr 2009 18:07:34 GMT


Claus Ibsen commented on CAMEL-1461:

>> The problem is that the replyTo is inherited from the very first from("activemq:queue:request")
when you send a replyTo JMS Message to it in the first place - then this replyTo is propagated
in the the route.
> from() becomes an INOUT only from the fact that the original message came with replyTo
!= null or you explicitly set a replyDestination as part of from() endpoint configuration.

> The fact that the user choose to set the replyTo destination in the original message
suggests that one wants to receive a reply to its original message. If the designer of the
Camel route decided to drop this
> replyTo then he has to explicitly state that in the contract. Had Michael done that he'd
be all set.
That is what he is in fact trying to do. He want to return a reply but at the same time send
a fire and forget message to a topic. To send this "fire and forget" message he should use
- wireTap
- inOnly
- to with pattern=InOnly

The problem is that when he does that Camel will propagate the original JMS headers along,
and then Camel itself sees that there is a JMSReplyTo and therefore it want to wait as well.

The original exchange will still be InOut and Camel will send a reply back. Its the _fire
and forget_ JMS message that is the problem. This cannot be cleanup done out of the box with
Camel if we revert the change, then you need to add clear all the JMS headers with a custom
HeaderFilterStategy or whatever. This is not very easy. The route explicit states that its
a _fire and forget_ and thus there should be *no* JMSReplyTo send.

The HeaderFilterStategy is a kinda advanced feature where you need to plug it in and add your
own java implementation. This is not desired for doing a very common route such as spin off
a _fire and forget_ while doing a JMS request/reply. 

> But you just broke the old contract and now people that use CamleTemplate to send JMS
messages with replyTo not null will have to set explicitQoSEnabled=true on the from()
> endpoint they send messages to! You will soon have people coming back and complaining
about what I just described.
What do you mean? If the use CamelTemplate and send a request/reply (eg requestXXX) then its
an InOut and then the from endpoint should not have any special options.

For instance in the code below:

String out = template.requestBody("activemq:queue:foo", "Hello", String.class);

Assuming the {{bye}} bean returns a response such as: {{ return "Bye World" }} then the {{out}}
String will contain the value returned = {{Bye World}}.

The method {{requestBody}} is used for *InOut* MEP and thus Camel will set a {{JMSReplyTo}}
when it send the {{Hello}} message to the JMS foo queue. And when Camel receives this message
it sees the JMSReplyTo and returns the response.

The contract is *not* broken.

>> What if the topic we sent to in the original sample is not based on Camel, then you
cannot disable reply to on this destination.
> Why not?
Why should Camel send a JMSReplyTo to a MQ destination in the first place where we *do not*
want a reply? Lets imagine the MQ destination is part of a production system you cannot change.
So what if it inspects this JMSReplyTo and want to send a reply that it was *never* intended
to send. It was after all just a _fire and forget_ message that was send to it. 

> A request route with a topic node incurs a 20 second wait and refers to the wrong MEP.
> --------------------------------------------------------------------------------------
>                 Key: CAMEL-1461
>                 URL:
>             Project: Apache Camel
>          Issue Type: Bug
>          Components: camel-jms
>    Affects Versions: 1.6.0
>         Environment: ActiveMQ/Camel
>            Reporter: Michael Chen
>            Assignee: Claus Ibsen
>             Fix For: 2.0.0, 1.6.1
> If a route contains a node that publishes to a topic, the route is incorrectly suspended
for a default 20 seconds at the topic node.  Further, checks the MEP of the
original request Exchange and not the endpoint of the topic.
> For example, say I have a route built like this:
> {code}
> from("activemq:queue:request").
>   to("generate_news").
>   to("activemq:topic:news").
>   to("do_something_else");
> {code}
> The original request is expecting a reply. However, after the "news" is pumped into the
news topic, there is a default 20 second wait (requestTimeout).  This wait always results
in the exception: "The OUT message was not received within: 20000 millis on the exchange..."

> After reading the JmsProducer code, I changed the route to the following:
> {code}
> from("activemq:queue:request").
>   to("generate_news").
>   to("activemq:topic:news?exchangePattern=InOnly").
>   to("do_something_else");
> {code}
> This reveals the root of the bug, which is in the first few lines of method org.apache.camel.component.jms.JmsProducer.process(Exchange):
> {code}//
>     public void process(final Exchange exchange) {
>         final org.apache.camel.Message in = exchange.getIn();
>         if (exchange.getPattern().isOutCapable()) {
> {code}
> The above if statement checks the MEP of the original request's Exchange and not the
new endpoint of the news topic. This makes the above "?exchangePattern=InOnly" configuration
useless, because the original request MEP is InOut.  The result is that after that 20 second
time-out, the temporary queue for the original request has expired, so the whole request failed.
Note that the next node "do_something_else" is never reached due to the time-out exception.

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