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"Superman is a slacker."

slacker is a simple RPC framework designed for Clojure and created by clojure.


  • Fast serialization based on Kryo (Text based serialization is also supported)
  • Security without additional policies
  • Transparent and non-invasive API
  • Extensible server with interceptor framework
  • Cluster with Zookeeper (moved to slacker-cluster)
  • Clean code


An pair of example server/client can be found under "examples", you can run the examples by lein run :server and lein run :client .



:dependencies [[slacker "0.8.0-SNAPSHOT"]]

Getting Started

Slacker will expose all your public functions under a given namespace.

(ns slapi)
(defn timestamp 
  "return server time in milliseconds"

;; ...more functions

To expose slapi, use:

(use 'slacker.server)
(start-slacker-server (the-ns 'slapi) 2104)

On the client side, define a facade for the remote function:

(use 'slacker.client)
(def sc (slackerc "localhost:2104"))
(use-remote 'sc 'slapi)

By checking the metadata of timestamp, you can find useful information:

(meta timestamp)
=> {:slacker-remote-name "timestamp", :slacker-remote-fn true,
:slacker-client #<SlackerClient
slacker.client.common.SlackerClient@575752>, :slacker-remote-ns
"slapi" :arglists ([]), :name timestamp 
:doc "return server time in milliseconds"}

Closing the client

(close-slackerc sc)

Options in defn-remote

You are specify the remote function name when the name is occupied in current namespace

(defn-remote sc remote-time
  :remote-ns "slapi"
  :remote-name "timestamp")

If you add an :async flag to defn-remote, then the facade will be asynchronous which returns a promise when you call it. You should deref it by yourself to get the return value.

(defn-remote sc slapi/timestamp :async true)

You can also assign a callback for an async facade.

(defn-remote sc slapi/timestamp :callback #(println %))

Serializing custom types

By default, most clojure data types are registered in carbonite. (As kryo requires you to register a class before you can serialize its instances.) However, you may have additional types to transport between client and server. To add your own types, you should register custom serializers on both server side and client side. Run this before you start server or client:

(use '[slacker.serialization])
(register-serializers {Class Serializer)

Carbonite has some detailed docs on how to create your own serializers.

JSON Serialization

Other than binary format, you can also use JSON for serialization. JSON is a text based format which is more friendly to human beings. It may be useful for debugging, or communicating with external applications.

Configure slacker client to use JSON:

(def sc (slackerc "localhost:2104" :content-type :json))

One thing you should note is the representation of keyword in JSON. Keywords and strings are both encoded as JSON string in transport. But while decoding, all map keys will be decoded to keyword, and all other strings will be decoded to clojure string. This may lead to inconsistency of your clojure data structure between server and client. Try to avoid this by carefully design your data structure or just using carbonite(default and recommended).

From slacker 0.4.0, clojure pr/read is supported. You can just set content-type as :clj. clojure pr/read has full support on clojure data structures and also easy for debugging. However, it's much slower that carbonite so you'd better not use it if you have critical performance requirements.

Server interceptors

To add custom functions on server, you can define custom interceptors before or after function called.

(definterceptor logging-interceptor 
   :before (fn [req] (println (str "calling: " (:fname req))) req))

(start-slacker-server (the-ns 'slapi) 2104
                      :interceptors (interceptors logging-interceptor))

For more information about using interceptors and creating your own interceptors, query the wiki page.

Slacker on HTTP

From 0.4.0, slacker can be configured to run on HTTP protocol. To enable HTTP transport, just add a :http option to your slacker server:

(start-slacker-server ...
                      :http 4104)

The HTTP url pattern is http://localhost:4104/namespace/function-name.format. Arguments are encoded in format, and posted to server via HTTP body. If you have multiple arguments, you should put them into a clojure vector (for clj format) or javascript array (for json format).

See a curl example:

$ curl -d "[5]" http://localhost:4104/slapi/rand-ints.clj
(38945142 1413770549 1361247669 1899499977 1281637740)

Note that you can only use json or clj as format. Because HTTP is a test based protocol, so carb won't be supported.

Access Control List

Slacker 0.7 supports IP based access control list (ACL). Consult wiki page for the ACL rule DSL.

Slacker Cluster


To test performance, just start an example server with lein run :server.

Then run the performance test script: lein exec scripts/performance-test.clj 200000 50. This will run 200,000 calls with 50 threads.

Tested on my working desktop (DELL optiplex 760, Intel(R) Core(TM)2 Duo CPU E7400 @ 2.80GHz, 8G memory), without any special JVM optimization. 200,000 calls with 50 threads is completed in 21923.806054 msecs, which means slacker could handle more than 9000 calls per second on this machine.



Copyright (C) 2011-2012 Sun Ning

Distributed under the Eclipse Public License, the same as Clojure.

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