Golang : Zip file

Go's standard library provides support for several archive file formats. Zip format is the most common standard of compressing file. It is easy to create/compress zip file in Go.

The package you need to import is

 archive/zip

and below is a simple Go program to compress file.

NOTE : The default compression level is 0(store), you have to change the compression algorithm to deflate(number 8). Otherwise, you will find that the created zip file size will be slightly larger!

go-zip.go

 package main

 import (
 "archive/zip"
 "flag"
 "fmt"
 "io"
 "os"
 )

 // use RegisterCompressor, if you plan to use your own compression algorithm
 // other that the standard algorithm 8(deflate)
 // the init block is commentted out as it is not used in this example
 //func init() {
 // see https://pkware.cachefly.net/webdocs/casestudies/APPNOTE.TXT
 // section 4.4.5 for the available compression methods...which are not implemented by Golang....
 // only algorithm 0 and number 8(deflate) available

 // var comp zip.Compressor
 // zip.RegisterCompressor(999, comp)
 //}

 func main() {
 flag.Parse()

 filename := flag.Arg(0)

 if filename == "" {
 fmt.Println("Usage go-zip sourcefile")
 os.Exit(1)
 }

 fmt.Printf("Zipping file. \n")

 err := zipfile(filename)

 if err != nil {
 fmt.Println(err)
 os.Exit(1)
 }

 fmt.Println("Zipped to ", filename+".zip")
 }

 func zipfile(filename string) error {

 newfile, err := os.Create(filename + ".zip")
 if err != nil {
 return err
 }
 defer newfile.Close()

 zipit := zip.NewWriter(newfile)

 defer zipit.Close()

 zipfile, err := os.Open(filename)
 if err != nil {
 return err
 }
 defer zipfile.Close()

 // get the file information
 info, err := zipfile.Stat()
 if err != nil {
 return err
 }

 header, err := zip.FileInfoHeader(info)
 if err != nil {
 return err
 }

 // default is Store 0(no compression!) 
 // forking important !!
 // change to deflate
 // see http://golang.org/pkg/archive/zip/#pkg-constants

 header.Method = zip.Deflate

 writer, err := zipit.CreateHeader(header)
 if err != nil {
 return err
 }
 _, err = io.Copy(writer, zipfile)
 return err

 }

test out the go-zip.go by >go run go-zip.go [filename]

Reference:

golang zip