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clojure-msgpack is a lightweight and simple library for converting between native Clojure data structures and MessagePack byte formats. clojure-msgpack only depends on Clojure itself; it has no third-party dependencies.


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  • pack: Serialize object as a sequence of java.lang.Bytes.
  • unpack Deserialize bytes as a Clojure object.
(require '[msgpack.core :as msg])
(require 'msgpack.clojure-extensions)

(msg/pack {:compact true :schema 0})
; => #<byte[] [B@60280b2e>

(msg/unpack (msg/pack {:compact true :schema 0}))
; => {:schema 0, :compact true}


clojure-msgpack provides a streaming API for situations where it is more convenient or efficient to work with byte streams instead of fixed byte arrays (e.g. size of object is not known ahead of time).

The streaming counterpart to msgpack.core/pack is msgpack.core/pack-stream which returns nil and accepts either or as an additional argument.

msgpack.core/unpack is in "streaming mode" when the argument is of type or

(use '

(with-open [s (output-stream "test.dat")]
  (msg/pack-stream {:compact true :schema 0} s))

(with-open [s (input-stream "test.dat")] (msg/unpack s))
; => {:schema 0, :compact true}

Core types

Clojure MessagePack
nil Nil
java.lang.Boolean Boolean
java.lang.Byte Integer
java.lang.Short Integer
java.lang.Integer Integer
java.lang.Long Integer
java.lang.BigInteger Integer
clojure.lang.BigInt Integer
java.lang.Float Float
java.lang.Double Float
java.math.BigDecimal Float
java.lang.String String
clojure.lang.Sequential Array
clojure.lang.IPersistentMap Map
msgpack.core.Ext Extended

Serializing a value of unrecognized type will fail with IllegalArgumentException. See Application types if you want to register your own types.

Clojure types

Some native Clojure types don't have an obvious MessagePack counterpart. We can serialize them as Extended types. To enable automatic conversion of these types, load the clojure-extensions library.

Clojure MessagePack
clojure.lang.Keyword Extended (type = 3)
clojure.lang.Symbol Extended (type = 4)
java.lang.Character Extended (type = 5)
clojure.lang.Ratio Extended (type = 6)
clojure.lang.IPersistentSet Extended (type = 7)

With msgpack.clojure-extensions:

(require 'msgpack.clojure-extensions)
(msg/pack :hello)
; => #<byte[] [B@a8c55bf>

Without msgpack.clojure-extensions:

(msg/pack :hello)
; => IllegalArgumentException No implementation of method: :pack-stream of
; protocol: #'msgpack.core/Packable found for class: clojure.lang.Keyword
; clojure.core/-cache-protocol-fn (core _deftype.clj:544)

You can also define your own Extended types with extend-msgpack.

(require '[msgpack.macros :refer [extend-msgpack]])

(defrecord Person [name])

  [p] (.getBytes (:name p))
  [bytes] (->Person (String. bytes)))

(msg/unpack (msg/pack [(->Person "bob") 5 "test"]))
; => (#user.Person{:name "bob"} 5 "test")


All pack and unpack functions take an optional map of options:

  • :compatibility-mode Serialize/deserialize strings and bytes using the raw-type defined here:

    Note: No error is thrown if an unpacked value is reserved under the old spec but defined under the new spec. We always deserialize something if we can regardless of compatibility-mode.

(msg/pack (byte-array (byte 9)) {:compatibility-mode true})


clojure-msgpack is MIT licensed. See the included LICENSE file for more details.


MessagePack implementation in Clojure /[Clojure]







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