main.go

package main

import (
	"archive/tar"
	"compress/gzip"
	"io"
	"os"
	"path/filepath"
)

func main() {
	var files []string
	root := "./data/"
	err := filepath.Walk(root, func(path string, info os.FileInfo, err error) error {
		if err != nil {
			panic(err)
		}

		if info.IsDir() {
			return nil
		}

		files = append(files, path)
		os.Stderr.WriteString("Adding file: " + path + "\n")

		return nil
	})
	if err != nil {
		panic(err)
	}

	file := os.Stdout
	err = createArchive(files, file)
	if err != nil {
		panic(err)
	}

	os.Stderr.WriteString("Done!\n")
}

func createArchive(files []string, buf io.Writer) error {
	// Create new Writers for gzip and tar
	// These writers are chained. Writing to the tar writer will
	// write to the gzip writer which in turn will write to
	// the "buf" writer
	gw := gzip.NewWriter(buf)
	defer gw.Close()
	tw := tar.NewWriter(gw)
	defer tw.Close()

	// Iterate over files and add them to the tar archive
	for _, file := range files {
		err := addToArchive(tw, file)
		if err != nil {
			return err
		}
	}

	return nil
}

func addToArchive(tw *tar.Writer, filename string) error {
	// Open the file which will be written into the archive
	file, err := os.Open(filename)
	if err != nil {
		return err
	}
	defer file.Close()

	// Get FileInfo about our file providing file size, mode, etc.
	info, err := file.Stat()
	if err != nil {
		return err
	}

	// Create a tar Header from the FileInfo data
	header, err := tar.FileInfoHeader(info, info.Name())
	if err != nil {
		return err
	}

	// Use full path as name (FileInfoHeader only takes the basename)
	// If we don't do this the directory strucuture would
	// not be preserved
	// https://golang.org/src/archive/tar/common.go?#L626
	header.Name = filename

	// Write file header to the tar archive
	err = tw.WriteHeader(header)
	if err != nil {
		return err
	}

	// Copy file content to tar archive
	_, err = io.Copy(tw, file)
	if err != nil {
		return err
	}

	return nil
}