How to parse a binary file in Go? Snippet based on MoPaQ SC2 replay parsing. Related blog post: http://www.jonathan-petitcolas.com/2014/09/25/parsing-binary-files-in-go.html

parsing-binary-file.go

package main

import (
    "bytes"
    "encoding/binary"
    "fmt"
    "log"
    "os"
)

type Header struct {
    UserDataMaxSize uint32
    HeaderOffset uint32
    UserDataSize uint32
    _ [5]byte
    Starcraft2 [22]byte
}

func main() {
    path := "replay.SC2Replay"

    file, err := os.Open(path)
    if err != nil {
        log.Fatal("Error while opening file", err)
    }

    defer file.Close()

    fmt.Printf("%s opened\n", path)

    formatName := readNextBytes(file, 4)
    fmt.Printf("Parsed format: %s\n", formatName)
    if string(formatName) != "MPQ\x1b" {
        log.Fatal("Provided replay file is not in correct format. Are you sure this is a SC2 replay file?")
    }

    header := Header{}
    data := readNextBytes(file, 39) //  3 * uint32 (4) + 5 * byte (1) + 22 * byte (1) = 43

    buffer := bytes.NewBuffer(data)
    err = binary.Read(buffer, binary.LittleEndian, &header)
    if err != nil {
        log.Fatal("binary.Read failed", err)
    }

    fmt.Printf("Parsed data:\n%+v\n", header)
}

func readNextBytes(file *os.File, number int) []byte {
    bytes := make([]byte, number)

    _, err := file.Read(bytes)
    if err != nil {
        log.Fatal(err)
    }

    return bytes
}