make tarball creation idempotent

pkg/pkg/utils.go

@@ -18,7 +18,17 @@ import (
 
 func TarballBTF(ctx context.Context, btf string, out string) error {
 	// Use external tool for performance reasons
-	return utils.RunCMD(ctx, filepath.Dir(btf), "tar", "cvfJ", out, filepath.Base(btf))
+	return utils.RunCMD(ctx, filepath.Dir(btf), "tar",
+		"-cvJ",
+		"--sort=name",
+		"--owner=root:0",
+		"--group=root:0",
+		"--mode=a=r",
+		"--mtime=@0",
+		"-f",
+		out,
+		filepath.Base(btf),
+	)
 }
 
 //

pkg/pkg/utils_test.go

@@ -0,0 +1,101 @@
+package pkg
+
+import (
+	"archive/tar"
+	"context"
+	"io"
+	"os"
+	"path/filepath"
+	"reflect"
+	"testing"
+
+	fastxz "github.com/therootcompany/xz"
+)
+
+const filename = "test.btf"
+
+func writeTarball(t *testing.T, out string, perm os.FileMode) (os.FileInfo, error) {
+	dir := t.TempDir()
+	btf := filepath.Join(dir, filename)
+	err := os.WriteFile(btf, []byte{1}, perm)
+	if err != nil {
+		return nil, err
+	}
+	err = TarballBTF(context.Background(), btf, out)
+	if err != nil {
+		return nil, err
+	}
+	stat, err := os.Stat(out)
+	if err != nil {
+		return nil, err
+	}
+	return stat, nil
+}
+
+func TestTarballIdempotent(t *testing.T) {
+	outdir := t.TempDir()
+	out1 := filepath.Join(outdir, "test1.btf.xz")
+	stat1, err := writeTarball(t, out1, 0666)
+	if err != nil {
+		t.Fatal(err)
+	}
+	out2 := filepath.Join(outdir, "test2.btf.xz")
+	stat2, err := writeTarball(t, out2, 0444)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// check .tar.xz file attributes that matter to git
+	if stat1.Size() != stat2.Size() {
+		t.Errorf("file sizes do not match. file1=%d file2=%d", stat1.Size(), stat2.Size())
+	}
+	if stat1.Mode() != stat2.Mode() {
+		t.Errorf("file modes do not match. file1=%s file2=%s", stat1.Mode(), stat2.Mode())
+	}
+
+	// check contents of file
+	data1, err := os.ReadFile(out1)
+	if err != nil {
+		t.Fatal(err)
+	}
+	data2, err := os.ReadFile(out2)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !reflect.DeepEqual(data1, data2) {
+		t.Errorf("tarball contents are not identical")
+	}
+
+	// inspect tar contents to ensure they match our requirements
+	f, err := os.Open(out1)
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() { _ = f.Close() })
+	xr, err := fastxz.NewReader(f, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	tr := tar.NewReader(xr)
+	for {
+		hdr, err := tr.Next()
+		if err == io.EOF {
+			break // End of archive
+		}
+		if err != nil {
+			t.Fatal(err)
+		}
+		if hdr.ModTime.Unix() != 0 {
+			t.Errorf("BTF file timestamp is not unix epoch. time=%s unix=%d", hdr.ModTime, hdr.ModTime.Unix())
+		}
+		if hdr.Mode != 0444 {
+			t.Errorf("BTF file mode is not 0444. mode=%o", hdr.Mode)
+		}
+		if hdr.Uid != 0 {
+			t.Errorf("BTF file owner is not UID 0. uid=%d", hdr.Uid)
+		}
+		if hdr.Gid != 0 {
+			t.Errorf("BTF file group is not GID 0. gid=%d", hdr.Gid)
+		}
+	}
+}