TL;DR

Langohr is a Clojure RabbitMQ client that embraces AMQP 0.9.1 Model.

1.0.0-beta14 is a development milestone release that includes a few minor features, mostly around error handling and recovery.

Changes between Langohr 1.0.0-beta13 and 1.0.0-beta14

Queueing Consumers

In its early days, Langohr has been using QueueingConsumer for langohr.queue/subscribe. It was later replaced by a DefaultConsumer implementation.

The key difference between the two is that

• QueueingConsumer blocks the caller
• with QueueingConsumer, deliveries are typically processed in the same thread

This implementation has pros and cons. As such, an implementation on top of QueueingConsumer is back with langohr.consumers/blocking-subscribe which is identical to langohr.consumers/subscribe in the signature but blocks the caller.

In addition, langohr.consumers/ack-unless-exception is a new convenience function that takes a delivery handler fn and will return a new function that explicitly acks deliveries unless an exception was raised by the original handler:

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(require '[langohr.consumers :as lc])
(require '[langohr.basic     :as lb])

(let [f  (fn [metadata payload]
           (comment "Message delivery handler"))
      f' (lc/ack-unless-exception f)]
  (lb/consume ch q (lc/create-default :handle-delivery-fn f'))

Contributed by Ian Eure.

Shutdown Signal Functions

Several new functions in langohr.shutdown aid with shutdown signals:

• langohr.shutdown/initiated-by-application?
• langohr.shutdown/initiated-by-broker?
• langohr.shutdown/reason-of
• langohr.shutdown/channel-of
• langohr.shutdown/connection-of

Clojure 1.5 By Default

Langohr now depends on org.clojure/clojure version 1.5.1. It is still compatible with Clojure 1.3 and if your project.clj depends on a different version, it will be used, but 1.5 is the default now.

We encourage all users to upgrade to 1.5, it is a drop-in replacement for the majority of projects out there.

Change Log

Langohr change log is available on GitHub.

Langohr is a ClojureWerkz Project

Langohr is part of the group of libraries known as ClojureWerkz, together with

• Elastisch, a minimalistic well documented Clojure client for ElasticSearch
• Welle, a Riak client with batteries included
• Monger, a Clojure MongoDB client for a more civilized age
• Neocons, a client for the Neo4J REST API
• Quartzite, a powerful scheduling library

and several others. If you like Langohr, you may also like our other projects.

Let us know what you think on Twitter or on the Clojure mailing list.

Michael on behalf of the ClojureWerkz Team