Detect compression type in Golang

main.go

package main

import (
        "flag"
        "log"
        "net/http"
        "os"
        "strings"
)

func main() {
        flag.Parse()
        sourcefile := flag.Arg(0)
        if sourcefile == "" {
                log.Fatalln("Miss file argument")
        }

        file, err := os.Open(sourcefile)
        if err != nil {
                log.Fatalln(err.Error())
        }
        defer file.Close()

        buff := make([]byte, 512)
        if _, err = file.Read(buff); err != nil {
                log.Fatalln(err.Error())
        }

        fileType := http.DetectContentType(buff)

        log.Println("http--> ", fileType)

        switch fileType {
        case "application/x-gzip":
                log.Println("gzip")
        case "application/zip":
                log.Println("zip")
        default:
                if strings.HasPrefix(string(buff), "\x42\x5a\x68") {
                        log.Println("bzip2")
                } else {
                        log.Println("text")
                }
        }
}