How can I use the “compress/gzip” package to gzip a file?

Question

I\'m new to Go, and can\'t figure out how to use the compress/gzip package to my advantage. Basically, I just want to write something to a file, gzip it and rea

Answer 1

I decided to combine ideas from others answers and just provide a full example program. Obviously there are many different ways to do the same thing. This is just one way:

package main

import (
    "compress/gzip"
    "fmt"
    "io/ioutil"
    "os"
)

var zipFile = "zipfile.gz"

func main() {
    writeZip()
    readZip()
}

func writeZip() {
    handle, err := openFile(zipFile)
    if err != nil {
        fmt.Println("[ERROR] Opening file:", err)
    }

    zipWriter, err := gzip.NewWriterLevel(handle, 9)
    if err != nil {
        fmt.Println("[ERROR] New gzip writer:", err)
    }
    numberOfBytesWritten, err := zipWriter.Write([]byte("Hello, World!\n"))
    if err != nil {
        fmt.Println("[ERROR] Writing:", err)
    }
    err = zipWriter.Close()
    if err != nil {
        fmt.Println("[ERROR] Closing zip writer:", err)
    }
    fmt.Println("[INFO] Number of bytes written:", numberOfBytesWritten)

    closeFile(handle)
}

func readZip() {
    handle, err := openFile(zipFile)
    if err != nil {
        fmt.Println("[ERROR] Opening file:", err)
    }

    zipReader, err := gzip.NewReader(handle)
    if err != nil {
        fmt.Println("[ERROR] New gzip reader:", err)
    }
    defer zipReader.Close()

    fileContents, err := ioutil.ReadAll(zipReader)
    if err != nil {
        fmt.Println("[ERROR] ReadAll:", err)
    }

    fmt.Printf("[INFO] Uncompressed contents: %s\n", fileContents)

    // ** Another way of reading the file **
    //
    // fileInfo, _ := handle.Stat()
    // fileContents := make([]byte, fileInfo.Size())
    // bytesRead, err := zipReader.Read(fileContents)
    // if err != nil {
    //     fmt.Println("[ERROR] Reading gzip file:", err)
    // }
    // fmt.Println("[INFO] Number of bytes read from the file:", bytesRead)

    closeFile(handle)
}

func openFile(fileToOpen string) (*os.File, error) {
    return os.OpenFile(fileToOpen, openFileOptions, openFilePermissions)
}

func closeFile(handle *os.File) {
    if handle == nil {
        return
    }

    err := handle.Close()
    if err != nil {
        fmt.Println("[ERROR] Closing file:", err)
    }
}

const openFileOptions int = os.O_CREATE | os.O_RDWR
const openFilePermissions os.FileMode = 0660

Having a full example like this should be helpful for future reference.