Purpose

The core MessagePack API provides simple pack and unpack methods for serializing and deserializing Ruby objects to and from binary format.

References

Concepts

Packing objects

Use Messagepack.pack to serialize Ruby objects to binary format:

Messagepack.pack({hello: "world"}) # => "\x81\xA5hello\xA5world"

Where,

  • Messagepack.pack accepts any Ruby object as its argument

  • The return value is a binary string containing the serialized data

  • Supported types include: nil, boolean, integer, float, string, array, hash, and any registered extension types

Unpacking data

Use Messagepack.unpack to deserialize binary data back to Ruby objects:

data = Messagepack.pack({hello: "world"})
Messagepack.unpack(data) # => {"hello"=>"world"}

Where,

  • Messagepack.unpack accepts a binary string or IO object

  • The return value is the original Ruby object

  • Extra bytes after the deserialized object will raise a Messagepack::MalformedFormatError

Supported types

Nil 

Messagepack.pack(nil) # => "\xC0"
Messagepack.unpack("\xC0") # => nil

Boolean 

Messagepack.pack(true)  # => "\xC3"
Messagepack.pack(false) # => "\xC2"
Messagepack.unpack("\xC3") # => true
Messagepack.unpack("\xC2") # => false

Integer

MessagePack supports integers from -2^63 to 2^64-1:

Messagepack.pack(0)   # => "\x00"
Messagepack.pack(127) # => "\x7F"
Messagepack.pack(128) # => "\xCC\x80"
Messagepack.pack(-1)  # => "\xFF"
Messagepack.unpack("\xCC\x80") # => 128

Float 

Messagepack.pack(3.14) # => "\xCB@\x09\x1E\xB8Q\xEB\x85\x1F"
Messagepack.unpack("\xCB@\x09\x1E\xB8Q\xEB\x85\x1F") # => 3.14

String

Strings are encoded as UTF-8:

Messagepack.pack("hello") # => "\xA5hello"
Messagepack.unpack("\xA5hello") # => "hello"

Array 

Messagepack.pack([1, 2, 3]) # => "\x93\x01\x02\x03"
Messagepack.unpack("\x93\x01\x02\x03") # => [1, 2, 3]

Hash 

Messagepack.pack({a: 1, b: 2}) # => "\x82\xA1a\x01\xA1b\x02"
Messagepack.unpack("\x82\xA1a\x01\xA1b\x02") # => {"a"=>1, "b"=>2}

Examples

Example 1. Using pack and unpack
# Serialize a complex object
data = {
  name: "Alice",
  age: 30,
  skills: ["Ruby", "Python"],
  metadata: {
    active: true,
    score: 95.5
  }
}

binary = Messagepack.pack(data)
# => "\x84\xA4name\xA5Alice\xA3age\x1E\xA6skills\
#     \x92\xA4Ruby\xA6Python\xA8metadata\x82\xA6active\
#     \xC3\xA5score\xCB@_\x00\x00"

# Deserialize back to a Ruby object
result = Messagepack.unpack(binary)
# => {"name"=>"Alice", "age"=>30, "skills"=>["Ruby", "Python"],
#     "metadata"=>{"active"=>true, "score"=>95.5}}

Aliases

The module also provides dump and load as aliases:

Messagepack.dump(data)  # Same as Messagepack.pack(data)
Messagepack.load(data)  # Same as Messagepack.unpack(data)