Request/reply with rest - solace

Question

I'm unable to implement request/reply pattern using rest protocol with solace.
I'm correctly receiving a request and I can see some headers like "solace-correlation-id" and "solace-message-id".
What I'm expecting is to return an http response with the body as message reply but I always get in my application:
org.apache.camel.ExchangeTimedOutException: The OUT message was not received within: 20000 millis due reply message with correlationID: xxxxx-1549904557890-0-26 not received on destination: #P2P/QTMP/v:cfdce68771f5/c9c4ba4a-a427-438a-9b7a-1f069608d13a.
Unfortunately the solace documentation only covers pub/sub pattern for rest but not the request/reply one.

Answer 1

There could be a few different things going on here.
Firstly try adding the log component between the "from" and "to" endpoints and again after the "to" endpoint as this will show you the headers of the reply, for example, using the Java DSL syntax:
from("{{fromSource}}" )
.to("log:all?level=INFO&showAll=true&multiline=true")
.to("{{toDest}}" )
.to("log:all?level=INFO&showAll=true&multiline=true")
;
I suspect the correlation id is not getting passed back. In my example I have a a NodeJS service so I set the following response header:
res.setHeader('solace-correlation-id', req.get('solace-correlation-id'));
With the additional logging, you should be able to see what is going wrong.

Answer 2

You are most likely missing the message ID or coorelation ID in your reply message.
https://docs.solace.com/RESTMessagingPrtl/Solace-REST-Message-Encoding.htm#2.2.6.1
When the Solace message broker receives a possible reply message routed to the HTTP client, it verifies that the reply message's message ID or correlation ID match those of the request message.
Specifically,
- the reply's message ID must match the request's message ID the
- reply's correlation ID must match the request's message ID, or the
- reply's correlation ID must match the request's correlation ID.
If any of those matches occur, the Solace message broker sends the reply message as an HTTP response to the HTTP client.
HTTP requires that there be exactly one HTTP response for each HTTP request, so each matching message ID or correlation ID can be used only in a single request-reply message exchange pattern.
If the reply message does not have a matching message ID or correlation ID as above, or if the reply message's matching message ID or correlation ID has already been consumed by an earlier reply message, the reply message is discarded.