Reading through a tar.gz file in Go / golang

tar-gz-reader.go

package main

import (
	"archive/tar"
	"compress/gzip"
	"flag"
	"fmt"
	"io"
	"os"
)

func main() {
	// get the arguments from the command line
	numPtr := flag.Int("n", 4, "an integer")
	flag.Parse()

	sourceFile := flag.Arg(0)

	if sourceFile == "" {
		fmt.Println("Dude, you didn't pass in a tar file!")
		os.Exit(1)
	}

	fmt.Println("arg 1: ", flag.Arg(0))

	processFile(sourceFile, *numPtr)
}

func processFile(srcFile string, num int) {
	f, err := os.Open(srcFile)
	if err != nil {
		fmt.Println(err)
		os.Exit(1)
	}
	defer f.Close()

	gzf, err := gzip.NewReader(f)
	if err != nil {
		fmt.Println(err)
		os.Exit(1)
	}

	tarReader := tar.NewReader(gzf)

	i := 0
	for {
		header, err := tarReader.Next()

		if err == io.EOF {
			break
		}

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

		name := header.Name

		switch header.Typeflag {
		case tar.TypeDir:
			continue
		case tar.TypeReg:
			fmt.Println("(", i, ")", "Name: ", name)
			if i == num {
				fmt.Println(" --- ")
				io.Copy(os.Stdout, tarReader)
				fmt.Println(" --- ")
				os.Exit(0)
			}
		default:
			fmt.Printf("%s : %c %s %s\n",
				"Yikes! Unable to figure out type",
				header.Typeflag,
				"in file",
				name,
			)
		}

		i++
	}
}

More over, it will fail in case the file is too large. (more than a couple of kb),

You need to change the Read/WriteFile into:
f, _ := os.Create(name)
defer f.Close()
io.Copy(f, tarReader)

This will safely copy everything. (just don't forget to make proper error handling)

EDIT: WARNING: this code (and the ones above) have path traversal vulnerability. Please read, understand and fix before using ANY OF THESE CODE SNIPPETS: https://snyk.io/research/zip-slip-vulnerability

Thank you all! Here's an improved non-buffering version with error checking that only takes in an io.Reader (works for files, HTTP responses etc.):

package tarextract

// hat tip https://gist.github.com/indraniel/1a91458984179ab4cf80

import (
	"archive/tar"
	"compress/gzip"
	"io"
	"log"
	"os"
)

func ExtractTarGz(gzipStream io.Reader) {
	uncompressedStream, err := gzip.NewReader(gzipStream)
	if err != nil {
		log.Fatal("ExtractTarGz: NewReader failed")
	}

	tarReader := tar.NewReader(uncompressedStream)

	for true {
		header, err := tarReader.Next()

		if err == io.EOF {
			break
		}

		if err != nil {
			log.Fatalf("ExtractTarGz: Next() failed: %s", err.Error())
		}

		switch header.Typeflag {
		case tar.TypeDir:
			if err := os.Mkdir(header.Name, 0755); err != nil {
				log.Fatalf("ExtractTarGz: Mkdir() failed: %s", err.Error())
			}
		case tar.TypeReg:
			outFile, err := os.Create(header.Name)
			if err != nil {
				log.Fatalf("ExtractTarGz: Create() failed: %s", err.Error())
			}
			defer outFile.Close()
			if _, err := io.Copy(outFile, tarReader); err != nil {
				log.Fatalf("ExtractTarGz: Copy() failed: %s", err.Error())
			}
		default:
			log.Fatalf(
				"ExtractTarGz: uknown type: %s in %s",
				header.Typeflag,
				header.Name)
		}
	}
}

How to write unit test for the same ?

I am working with symbolic links so I took the liberty to add a case for those to @joonas-fi's solution. Simple addition, but it works and I hope it helps someone :)

package tarextract

// hat tip https://gist.github.com/indraniel/1a91458984179ab4cf80

import (
	"archive/tar"
	"compress/gzip"
	"io"
	"log"
	"os"
)

func ExtractTarGz(gzipStream io.Reader) {
	uncompressedStream, err := gzip.NewReader(gzipStream)
	if err != nil {
		log.Fatal("ExtractTarGz: NewReader failed")
	}

	tarReader := tar.NewReader(uncompressedStream)

	for true {
		header, err := tarReader.Next()

		if err == io.EOF {
			break
		}

		if err != nil {
			log.Fatalf("ExtractTarGz: Next() failed: %s", err.Error())
		}

		switch header.Typeflag {
		case tar.TypeDir:
			if err := os.Mkdir(header.Name, 0755); err != nil {
				log.Fatalf("ExtractTarGz: Mkdir() failed: %s", err.Error())
			}
		case tar.TypeReg:
			outFile, err := os.Create(header.Name)
			if err != nil {
				log.Fatalf("ExtractTarGz: Create() failed: %s", err.Error())
			}
			defer outFile.Close()
			if _, err := io.Copy(outFile, tarReader); err != nil {
				log.Fatalf("ExtractTarGz: Copy() failed: %s", err.Error())
			}
                case tar.TypeSymlink:
                        os.Symlink(header.Linkname, header.Name)
		default:
			log.Fatalf(
				"ExtractTarGz: uknown type: %s in %s",
				header.Typeflag,
				header.Name)
		}
	}
}

Thanks for sharing @dkartachov, have a nice day :)

I echo @joonas-fi, thanks for the improvements @dkartachov !