Full support for async messaging and correlation
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Key: CAMEL-1336
URL: https://issues.apache.org/activemq/browse/CAMEL-1336
Project: Apache Camel
Issue Type: Improvement
Components: camel-core
Affects Versions: 1.5.0
Reporter: Hadrian Zbarcea
Priority: Critical
This is a feature that has been requested by users a few times, and it's time
to get addressed.
Camel does not really support 2x 1-way async messaging. It sorta does in
camel-jms, by sending a message to a queue and setting the "JMSCorrelationID"
header. For a ExchangePattern.InOut it immediately waits for a response (up to
a timeout period) and gets the reply and continues processing.
There are a few issues with this approach:
* this mechanism is not available across all camel components. There are other
camel components that support async 1 way messaging such as file/ftp, mail,
mina, cxf, etc.
* there can be no other processing between a message is sent and a reply is
received.
* the timeout value is short and keeps resources locked, we cannot have long
running transactions
My proposal is to:
* move the mechanism from jms into core (and improve it)
* use a correlation mechanism (that will be different for different components,
such as MessageID in camel-mail) to correlate inputs with outputs. The
correlation mechanism could be implicit or explicit.
* provide a storage for pending 2x 1-way async UOWs (multiple options available)
A route would then look something like this:
{code}
from("direct.start")
.setHeader("reply-to", constant("hadr...@localhost; c...@localhost"))
.correlate(header("Message-ID"))
.to("smtp://some...@localhost?password=secret&to=other...@localhost")
from("pop3://hadr...@localhost?password=secret).correlate(header("Message-ID"))
.from("some-other-source")
.aggregate(header("foo")).to("direct:end");
{code}
*note*: the multiple from(s).
* This also gives unlimited time for a reply to be received.
* I don't think support for acid transactions makes any sense in such case.
* The presence of correlate() in the pipeline causes automatic storage of the
uow
* The presence of correlate() after a from() causes the removal of the uow from
persistent store.
Any ideas?
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