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MessagePack Code Generator and Library for Go

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This is a code generation tool and serialization library for MessagePack. You can read more about MessagePack in the wiki or at

This library is no longer being maintained. You should be using Protocol Buffers for binary data serialization

Top Features

  • Use Go as your schema language
  • Performance is amazing
  • JSON interoperability
  • Type safety
  • Support for complex type declarations
  • Define your own MessagePack extensions
  • Automatic unit test and benchmark generation
  • Native support for Go’s time.Time, complex64, and complex128 types
  • Preprocessor directives
  • Generation of both []byte-oriented and io.Reader/io.Writer-oriented methods


In a Go code source file, include the following directive:

//go:generate msgp

Within the directory with the file where you placed that directive, run go generate.

The msgp command will tell the go generate tool to generate serialization and deserialization methods (functions) for all exported types in the file. These custom-built functions enable you to use package msgp to efficiently encode objects to and from the MessagePack format.

You can read more about the code generation options here.


Struct field names can be set the same way as with the encoding/json package. For example:

type Person struct {
    Name       string `msgp:"name"`
    Address    string `msgp:"address"`
    Age        int    `msgp:"age"`
    Hidden     string `msgp:"-"` // this field is ignored
    unexported bool              // this field is also ignored

(The struct field tags are optional.)

By default, the code generator will satisfy msgp.Sizer, msgp.Encoder, msgp.Decoder, msgp.Marshaler, and msgp.Unmarshaler. You’ll often find that much marshalling and unmarshalling will be done with zero heap allocations.

Although msgp.Marshaler and msgp.Unmarshaler are similar to the standard library’s json.Marshaler and json.Unmarshaler, msgp.Encoder and msgp.Decoder are useful for stream serialization. (*msgp.Writer and *msgp.Reader are essentially protocol-aware versions of *bufio.Writer and *bufio.Reader.)

Consider the following:

const Eight = 8
type MyInt int
type Data []byte

type Struct struct {
    Which  map[string]*MyInt `msgp:"which"`
    Other  Data              `msgp:"other"`
    Nums   [Eight]float64    `msgp:"nums"`

As long as the declarations of MyInt and Data are in the same file as Struct, the parser will determine that the type information for MyInt and Data can be passed into the definition of Struct before its methods are generated.


MessagePack supports defining your own types through "extensions," which are just a tuple of the data "type" (int8) and the raw binary. You can see a worked example in the wiki.


The code generator here and runtime library are both stable. Newer versions of the code may generate different code than older versions for performance reasons.

You can read more about how msgp maps MessagePack types onto Go types in the wiki.

Here some of the known limitations/restrictions:

  • Identifiers from outside the processed source file are assumed to satisfy the generator's interfaces. If this isn't the case, your code will fail to compile.
  • The chan and func fields and types are ignored as well as un-exported fields.
  • Encoding of interface{} is limited to built-ins or types that have explicit encoding methods.
  • Maps must have string keys. This is intentional (as it preserves JSON interoperability). Although non-string map keys are not forbidden by the MessagePack standard, many serializers impose this restriction. (It also means any well-formed struct can be decoded into a map[string]interface{}.) The only exception to this rule is that the decoders will allow you to read map keys encoded as bin types, since some legacy encodings permitted this. (However, those values will still be cast to Go strings, and they will be converted to str types when re-encoded. It is the responsibility of the user to ensure that map keys are UTF-8 safe in this case.) The same rules hold true for JSON translation.

If the output compiles, then there's a pretty good chance things are fine. (Plus, we generate tests for you.) Please file an issue if you think the generator is writing broken code.


If you like benchmarks, see here, here, and here.


This repository is a fork of

Differences between this tool and tinylib/msgp:

  • Here we have regular expression matching for type names in directives.
  • Here we do not use package unsafe for conversions from byte slices to strings: []byte is converted quite efficiently to string simply with the built-in string().
  • This codebase is thoroughly refactored to be more Go-idiomatic and efficient.

You're welcome to contribute!

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