[rabbitmq-discuss] Durable queues for STOMP broker

[Sean Treadway]

Hi all,

I was pleased to find a STOMP broker to rabbitmq is under works,  
however the default queue creation parameters didn't meet my initial  
assumptions for using the broker as a reliable task dispatcher.   
Digging through the code, I found that the queues were always being  
created as non-durable and auto-deleted - any persistent messages  
would be discarded when no consumers were subscribed.  For our  
application, we needed to save these messages and process them at well  
defined intervals as well as have restart tolerant reliability.

Attached are 2 patches from my findings on how to expose some of the  
method parameters as STOMP headers.  They include the following changes:

  * utility function to extract boolean header values
  * expose 'passive', 'durable', 'auto-delete', 'exclusive' parameters  
of the AMQP 'queue.declare' method as STOMP headers in SUBSCRIBE
  * persist non AMQP binary content properties
  * test sender and receiver for durable queues

The simple reproduction case is as follows:

  * Connect a consumer and subscribe with the following headers:

SUBSCRIBE
destination: /queue/test
auto-delete: false
durable: true

  * Disconnect the consumer
  * Start a producer and send some persistent messages:

SEND
destination: /queue/test
delivery-mode: 2
content-length: 5
content-type: text/plain

ohai!

* Connect a consumer and subscribe to the queue with any headers

You should receive the persisted message sent to /queue/test.  There  
are 2 files in priv/tests-ruby that show this behavior a little bit  
better.  Comments are in persistent-sender.rb.

I also found a bug in message persistence over server restarts in  
rabbitmq-1.3.0.  In the comments for the content record, it states  
that at most, one of properties and properties_bin can be 'none'.   
During message persistence, it looked like there was an assumption  
that all properties came from AMQP binary packed blobs and the parsed  
headers were always cleared without checking that they could be  
restored later.  This patch will maintain the existing content/ 
properties when properties_bin is 'none'.  As well as fixing the stomp  
broker, this may fix persistence bugs with other erlang brokers that  
speak directly to rabbit_channel:do/3.

Without the patch, when the durable queues were restored and the  
persisted messages were resent, the content properties (including the  
STOMP headers) were lost and no longer matched by  
rabbit_stomp:send_reply/3 - logging an error and consuming the  
message.  With the patch, the persisted messages are are properly  
restored and resent to the first subscriber.

To reproduce this:

Run persistent-receiver.rb once - interrupt.
Run persistent-sender.rb once
Stop all running nodes of rabbitmq
Start rabbitmq
Run persistent-receiver.rb - you should receive the messages

Big thanks to you all at LShift for building this beautiful code.  My  
familiarity with AMQP is still fresh so feedback on the applicability  
of these patches is very welcome.  Points I am unsure about are - the  
role of the 'passive' parameter to queue.declare, whether or not to  
expose the 'nowait' parameter, whether or not to try and match  
ActiveMQ's STOMP header names or stick with the AMQP naming,  
interoperability of the properties patch for brokers such as HTTP and  
regression of the properties patch against AMQP messages with binary  
properties.  Also, the STOMP spec gives no insight for queue deletion  
when a durable queue is no longer needed.  Any ideas for that one?

Thanks,
-Sean

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