packer

README

packer

Overview

This library is for packing/unpacking structs(i.e. serialize struct to binary) in classical protocol style mostly used in C (e.g. bitcoiin protocol).

Requirements

This requires

• git
• go 1.3+

Supported types in Struct

• uint16/32/64
• byte
• byte slice
• VarInt
• string(automatically prefixed by length)
• struct slice

You must specify how size of slice is serialized to binary by struct tag named len.

• len:"<number>" : fixed size (e.g. len:"5")
• len:"lastnum" : The size of slice is specified at last field in struct.
• len:"prefix : The size of slice is prefixed.

When you pack slices in struct and use "lastnum" , pack will NOT automatically adds the sizes of slices. You must specify the size manually. If you use "prefix", the size is automatically prefixed. The length of fixed size is not packed.

Length of non-slice types(e.g. size 8 of uint64 etc) is not packed.

All integers are packed in little endian.

Installation

 $ go get github.com/bitgoin/packer

Example

(This example omits error handlings for simplicity.)

import "git.gurkengewuerz.de/bitgoin/utils/packer"

type S3 struct {
	B byte
}

type S1 struct {
	I64 uint64
	VB1 []byte `len:"5"`
	VI1 packer.VarInt
	VS  string
	ST  S3
	STA []S3 `len:"2"`
	STB []S3 `len:"prefix"`
}

var s1 = S1{
	12345,
	[]byte{0x12, 0x34, 0x45, 0x00, 0x00},
	packer.VarInt(6),
	"abcde",
	S3{
		0x12,
	},
	[]S3{
		{0x34}, {0x35},
	},
	[]S3{
		{0x21}, {0x22},
	},
}
var result = []byte{
	0x39, 0x30, 0, 0, 0, 0, 0, 0, //uint64(12345)
	0x12, 0x34, 0x45, 0x00, 0x00, //fixed size of slice, no length is packed.
	0x06, 0x00, //VarInt(6)
	0x05,                         //size of string(abcde)
	0x61, 0x62, 0x63, 0x64, 0x65, //string("abcde")
	0x12,             //struct S3{byte(0x12)}
	0x34,0x35         //fixed size of []S3
	0x02,  //size of []S3
	0x21, 0x22, //struct []S3
}

func main(){
	var buf bytes.Buffer
	err := Pack(&buf, s1)

	s2 := S1{}
	r := bytes.NewBuffer(result)
	err := Unpack(r, &s2)

}

Contribution

Improvements to the codebase and pull requests are encouraged.

Documentation

Index

• func Pack(buf io.Writer, t interface{}) error
• func Unpack(buf io.Reader, t interface{}) error
• type VarInt

Functions

func Pack

func Pack(buf io.Writer, t interface{}) error

Pack converts struct to []byte.

func Unpack

func Unpack(buf io.Reader, t interface{}) error

Unpack converts []byte to struct.

Types

type VarInt

type VarInt uint64

VarInt is variable integer in bitcoin protocol.