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Colfer Build Status

Colfer is a binary serialization format optimized for speed and size.

The project's compiler colf(1) generates source code from schema definitions to marshal and unmarshall data structures.

This is free and unencumbered software released into the public domain. The format is inspired by Protocol Buffer.

Language Support

  • C, ISO/IEC 9899:2011 compliant a.k.a. C11, C++ compatible
  • Go, a.k.a. golang
  • Java, Android compatible
  • JavaScript, a.k.a. ECMAScript, NodeJS compatible


  • Simple and straightforward in use
  • No dependencies other than the core library
  • Both faster and smaller than: Protocol Buffers, FlatBuffers and MessagePack
  • Robust including size protection
  • Maximum of 127 fields per data structure
  • No support for enumerations
  • Framed; suitable for concatenation/streaming


  • Rust and Python
  • List support for integers and timestamps


Download a prebuilt compiler or run go get -u to make one yourself. Without arguments the command prints its manual.

	colf — compile Colfer schemas

	colf [ options ] language [ file ... ]

	Generates source code for a language. The options are: C, Go,
	Java and JavaScript.
	The file operands specify the input. Directories are scanned for
	files with the colf extension. If file is absent, colf includes
	the working directory.
	A package can have multiple schema files.

  -b directory
    	Use a specific destination base directory. (default ".")
  -f	Normalizes schemas on the fly.
  -l expression
    	Sets the default upper limit for the number of elements in a
    	list. The expression is applied to the target language under
    	the name ColferListMax. (default "64 * 1024")
  -p prefix
    	Adds a package prefix. Use slash as a separator when nesting.
  -s expression
    	Sets the default upper limit for serial byte sizes. The
    	expression is applied to the target language under the name
    	ColferSizeMax. (default "16 * 1024 * 1024")
  -v	Enables verbose reporting to the standard error.
  -x class
    	Makes all generated classes extend a super class. Use slash as
    	a package separator. Java only.

	The command exits 0 on succes, 1 on compilation failure and 2
	when invoked without arguments.

	Compile ./io.colf with compact limits as C:

		colf -b src -s 2048 -l 96 C io.colf

	Compile ./api/*.colf in package com.example as Java:

		colf -p com/example -x com/example/Parent Java api

	Report bugs at

	Text validation is not part of the marshalling and unmarshalling
	process. C and Go just pass any malformed UTF-8 characters. Java
	and JavaScript replace unmappable content with the '?' character
	(ASCII 63).


It is recommended to commit the generated source code to the respective version control.

Alternatively, you may use the Maven plugin.



Data structures are defined in .colf files. The format is quite conventional.

// Package demo offers a demonstration.
// These comment lines will end up in the generated code.
package demo

// Course is the grounds where the game of golf is played.
type course struct {
	ID    uint64
	name  text
	holes []hole
	image binary
	tags  []text

type hole struct {
	// Lat is the latitude of the cup.
	lat float64
	// Lon is the longitude of the cup.
	lon float64
	// Par is the difficulty index.
	par uint8
	// Water marks the presence of water.
	water bool
	// Sand marks the presence of sand.
	sand bool

See what the generated code looks like in C, Go, Java or JavaScript.

The following table shows how Colfer data types are applied per language.

Colfer C Go Java JavaScript
bool char bool boolean Boolean
uint8 uint8_t uint8 byte † Number
uint16 uint16_t uint16 short † Number
uint32 uint32_t uint32 int † Number
uint64 uint64_t uint64 long † Number ‡
int32 int32_t int32 int Number
int64 int64_t int64 long Number ‡
float32 float float32 float Number
float64 double float64 double Number
timestamp timespec time.Time †† time.Instant Date + Number
text const char* + size_t string String †‡ String †‡
binary uint8_t* + size_t []byte byte[] Uint8Array
list * + size_t slice array Array
  • † signed representation of unsigned data, i.e. may overflow to negative.
  • ‡ range limited to (1 - 2⁵³, 2⁵³ - 1)
  • †† timezone not preserved
  • †‡ characters limited by UTF-16 (U+0000, U+10FFFF)

Lists may contain floating points, text, binaries or data structures.


Name changes do not affect the serialization format. Deprecated fields should be renamed to clearly discourage their use. For backwards compatibility new fields must be added to the end of colfer structs. Thus the number of fields can be seen as the schema version.


Colfer aims to be the fastest and the smallest format while still resilient to malicious input. See the benchmark wiki for a comparison. Suboptimal performance is treated like a bug.