Compress docker artifacts with gzip

dev-tools/mage/dockerbuilder.go

@@ -18,8 +18,12 @@
 package mage
 
 import (
+	"bytes"
+	"compress/gzip"
 	"fmt"
+	"io"
 	"os"
+	"os/exec"
 	"path/filepath"
 	"strings"
 
@@ -141,13 +145,47 @@ func (b *dockerBuilder) dockerSave(tag string) error {
 	// Save the container as artifact
 	outputFile := b.OutputFile
 	if outputFile == "" {
-		outputTar, err := b.Expand(defaultBinaryName + ".docker.tar")
+		outputTar, err := b.Expand(defaultBinaryName + ".docker.tar.gz")
 		if err != nil {
 			return err
 		}
 		outputFile = filepath.Join(distributionsDir, outputTar)
 	}
-	if err := sh.Run("docker", "save", "-o", outputFile, tag); err != nil {
+	var stderr bytes.Buffer
+	cmd := exec.Command("docker", "save", tag)
+	cmd.Stderr = &stderr
+	stdout, err := cmd.StdoutPipe()
+	if err != nil {
+		return err
+	}
+	if err = cmd.Start(); err != nil {
+		return err
+	}
+
+	err = func() error {
+		f, err := os.Create(outputFile)
+		if err != nil {
+			return err
+		}
+		defer f.Close()
+
+		w := gzip.NewWriter(f)
+		defer w.Close()
+
+		_, err = io.Copy(w, stdout)
+		if err != nil {
+			return err
+		}
+		return nil
+	}()
+	if err != nil {
+		return err
+	}
+
+	if err = cmd.Wait(); err != nil {
+		if errmsg := strings.TrimSpace(stderr.String()); errmsg != "" {
+			err = errors.Wrap(errors.New(errmsg), err.Error())
+		}
 		return err
 	}
 	return errors.Wrap(CreateSHA512File(outputFile), "failed to create .sha512 file")

dev-tools/packaging/package_test.go

@@ -80,7 +80,8 @@ func TestDeb(t *testing.T) {
 }
 
 func TestTar(t *testing.T) {
-	tars := getFiles(t, regexp.MustCompile(`\.tar\.gz$`))
+	// Regexp matches *-arch.tar.gz, but not *-arch.docker.tar.gz
+	tars := getFiles(t, regexp.MustCompile(`-\w+\.tar\.gz$`))
 	for _, tar := range tars {
 		checkTar(t, tar)
 	}
@@ -94,7 +95,7 @@ func TestZip(t *testing.T) {
 }
 
 func TestDocker(t *testing.T) {
-	dockers := getFiles(t, regexp.MustCompile(`\.docker.tar$`))
+	dockers := getFiles(t, regexp.MustCompile(`\.docker\.tar\.gz$`))
 	for _, docker := range dockers {
 		checkDocker(t, docker)
 	}
@@ -514,7 +515,13 @@ func readDocker(dockerFile string) (*packageFile, *dockerInfo, error) {
 	var info *dockerInfo
 	layers := make(map[string]*packageFile)
 
-	tarReader := tar.NewReader(file)
+	gzipReader, err := gzip.NewReader(file)
+	if err != nil {
+		return nil, nil, err
+	}
+	defer gzipReader.Close()
+
+	tarReader := tar.NewReader(gzipReader)
 	for {
 		header, err := tarReader.Next()
 		if err != nil {