Golang : zlib compress file example

This tutorial will show you how to read an uncompress file content into a buffer, use zlib on the buffer and write out the buffer content into a new file.

Here we go :

 package main

 import (
 "bufio"
 "bytes"
 "compress/zlib"
 "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-zlib 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 := zlib.NewWriter(&buf)
 writer.Write(rawbytes)
 writer.Close()

 err = ioutil.WriteFile(filename+".zlib", 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+".zlib")

 }

References :

http://golang.org/pkg/compress/zlib/

https://www.socketloop.com/tutorials/golang-read-binary-file-into-memory