What is Fixed-Width Binary Encoding

Fixed-Width Binary Encoding is a data structure not often seen in web development.

Getting Started

When data is transferred between parties, the convention is a key value pair structure eg.

{
    userId: "191B2E92-3E2A-4473-B848-8E8D07046FD7",
    attending: true,
    Date: 1750021782
}

If this data example was converted into bytes as is, it would look like:

package main

import (
	"encoding/json"
	"fmt"
)

type UserAttendanceRecord struct {
	UserID    string `json:"userId"`
	Attending bool   `json:"attending"`
	Date      int64  `json:"date"`
}

func main() {
	record := UserAttendanceRecord{
		UserID:    "191B2E92-3E2A-4473-B848-8E8D07046FD7",
		Attending: true,
		Date:      1750021782,
	}

	bytes, err := json.Marshal(record)
	if err != nil {
		panic(err)
	}

	fmt.Printf("Total length: %d bytes\n", len(bytes))
}

Total length: 84 bytes

Fixed-Width Binary Encoding

Fixed-Width Binary Encoding stores data in an array of bytes without identifiers. Because there are no identifiers, the order and length of the data in the array follows a predefined structure.

Fixed-Width Binary Encoded arrays are used in cryptographic processes where data length is standardized and data transfer efficiency is paramount. An example specification is below.

User Attendance Data

userAttendanceRecord := {
    userId: "191B2E92-3E2A-4473-B848-8E8D07046FD7",
    attending: true,
    Date: 1750021782
}

func process() {
	hexStr := "191B2E923E2A4473B8488E8D07046FD7"
	userID, err := hex.DecodeString(hexStr)
	if err != nil {
		panic(err)
	}

	attending := []byte{1}

	date := make([]byte, 4)
	binary.LittleEndian.PutUint32(date, 1750021782)

	pbe := append(userID, attending...)
	pbe = append(pbe, date...)

    return pbe
}

Total length: 21 bytes

The receiver of the data would use the API specs above to decode the provided byte array back into their original value.