The ClojureWerkz Blog

News and updates about ClojureWerkz projects

Langohr 2.0.0 Is Released


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

2.0.0 is a major release that introduces automatic topology (queues, exchanges, bindings, and consumers) recovery.

Making Automatic Connection Recovery More Awesome

Langohr 1.7.0 supports automatic recovery of connections and channels when network connectivity fails. However, recovery of queues, exchanges, bindings and consumers was up to developers. In most cases, topology recovery consists of a few straightforward steps:

  • Re-declare queues
  • Re-declare exchanges
  • Re-establish bindings
  • Re-register consumers

Langohr 2.0 provides a feature that performs those steps automatically. Every channel now tracks the entities declared on it and re-declares them after recovery. It’s possible to disable this feature and perform manual recovery, just like before.

For many applications, recovery from network and node failures will now be almost effortless. Give it a try and let us know how it goes!

Changes between Langohr 1.7.0 and 2.0.0

Topology (Queues, Exchanges, Bindings, Consumers) Recovery

Connection recovery now supports entity recovery. Queues, exchanges, bindings and consumers can be recovered automatically after channel recovery. This feature is enabled by default and can be disabled by setting the :automatically-recover-topology option to false.

:requested-channel-max Connection Option

:requested-channel-max is a new option accepted by langohr.core/connect that configures how many channels this connection may have. The limit is enforced on the client side. 0 means “no limit” and is the default.

Contributed by Glophindale.


langohr.queue/empty? is a new function that returns true if provided queue is empty (has 0 messages ready):

(require '[langohr.queue :as lq])

(lq/empty? ch "a.queue")
;= true


langohr.core/add-shutdown-listener is a helper function that reifies and registers a shutdown signal listener on a connection.


langohr.core/add-blocked-listener is a helper function that reifies and registers a connection.blocked and connection.unblocked listener on a connection.

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
  • Cassaforte, a Clojure Cassandra client built around CQL 3.0
  • 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