Golang : Gzip file example

This tutorial is to fulfill a request from a student learning Golang in Senegal.

His question is how to gzip a file in Golang. Most of the online articles he found only show how to compress some bytes of text but not how to compress a file. This tutorial will show how to read an uncompress file content into a buffer, gzip the buffer and write out the buffer content into a new file.

Here we go :

 package main

 import (
 "bufio"
 "bytes"
 "compress/gzip"
 "flag"
 "fmt"
 "io/ioutil"
 "os"
 )

 func main() {

 flag.Parse() // get the arguments from command line

 filename := flag.Arg(0)

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

 rawfile, err := os.Open(filename)

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

 // calculate the buffer size for rawfile
 info, _ := rawfile.Stat()

 var size int64 = info.Size()
 rawbytes := make([]byte, size)

 // read rawfile content into buffer
 buffer := bufio.NewReader(rawfile)
 _, err = buffer.Read(rawbytes)

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

 var buf bytes.Buffer
 writer := gzip.NewWriter(&buf)
 writer.Write(rawbytes)
 writer.Close()

 err = ioutil.WriteFile(filename+".gz", buf.Bytes(), info.Mode())
 // use 0666 to replace info.Mode() if you prefer

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

 fmt.Printf("%s compressed to %s\n", filename, filename + ".gz")

 }

Sample tests result :