diff --git a/taildrop/utils_test.go b/taildrop/utils_test.go
new file mode 100644
index 000000000..b54ea6899
--- /dev/null
+++ b/taildrop/utils_test.go
@@ -0,0 +1,131 @@
+package taildrop
+
+import (
+	"archive/tar"
+	"github.com/google/go-cmp/cmp"
+	"github.com/stretchr/testify/assert"
+	"io"
+	"os"
+	"path/filepath"
+	"slices"
+	"strings"
+	"tailscale.com/util/must"
+	"testing"
+)
+
+func TestTarArchiveUtils(t *testing.T) {
+	equalErrorPrefix := func(err error, prefix string) {
+		t.Helper()
+		assert.Error(t, err)
+		assert.True(t, strings.HasPrefix(err.Error(), prefix))
+	}
+
+	var autoCloser []io.ReadCloser
+	defer func() {
+		for _, r := range autoCloser {
+			_ = r.Close()
+		}
+	}()
+
+	readerFromFile := func(file string) io.ReadCloser {
+		t.Helper()
+		f, err := os.Open(file)
+		must.Do(err)
+		autoCloser = append(autoCloser, f)
+		return f
+	}
+
+	writeToFile := func(reader io.Reader, file string) {
+		t.Helper()
+		outFile, err := os.Create(file)
+		must.Do(err)
+		defer outFile.Close()
+
+		_, err = io.Copy(outFile, reader)
+		must.Do(err)
+	}
+
+	checkDirectory := func(dir string, want ...string) {
+		t.Helper()
+		var got []string
+		for _, de := range must.Get(os.ReadDir(dir)) {
+			got = append(got, de.Name())
+		}
+		slices.Sort(got)
+		slices.Sort(want)
+		if diff := cmp.Diff(got, want); diff != "" {
+			t.Fatalf("directory mismatch (-got +want):\n%s", diff)
+		}
+	}
+
+	checkTarArchive := func(tarFile string, want ...string) {
+		t.Helper()
+		r := tar.NewReader(readerFromFile(tarFile))
+
+		var got []string
+		for {
+			header, err := r.Next()
+			if err == io.EOF {
+				break // extract finished
+			}
+			must.Do(err)
+			got = append(got, header.Name)
+		}
+		slices.Sort(got)
+		slices.Sort(want)
+		if diff := cmp.Diff(got, want); diff != "" {
+			t.Fatalf("TAR archive mismatch (-got +want):\n%s", diff)
+		}
+	}
+
+	dir := t.TempDir()
+	must.Do(os.MkdirAll(filepath.Join(dir, "root-dir"), 0644))
+	must.Do(os.WriteFile(filepath.Join(dir, "root-dir/foo.txt"), []byte("This is foo.txt"), 0644))
+	must.Do(os.WriteFile(filepath.Join(dir, "root-dir/bar"), []byte("This is bar"), 0644))
+	must.Do(os.WriteFile(filepath.Join(dir, "root-dir/其他文字.docx"), []byte(""), 0644))
+	must.Do(os.MkdirAll(filepath.Join(dir, "root-dir/sub-dir"), 0644))
+	must.Do(os.WriteFile(filepath.Join(dir, "root-dir/sub-dir/buzz.log"), []byte("hello world..."), 0644))
+
+	// Test Directory Compression
+	tarPath := filepath.Join(dir, "root-dir.tscompresseddir")
+
+	reader, err := GetCompressedDirReader(filepath.Join(dir, "root-dir"))
+	must.Do(err)
+	writeToFile(reader, tarPath)
+	checkTarArchive(tarPath, "root-dir", "root-dir/foo.txt", "root-dir/bar", "root-dir/其他文字.docx",
+		"root-dir/sub-dir", "root-dir/sub-dir/buzz.log")
+
+	reader, err = GetCompressedDirReader(filepath.Join(dir, "./foo/bar/../../root-dir/sub/.."))
+	must.Do(err)
+	writeToFile(reader, tarPath)
+	checkTarArchive(tarPath, "root-dir", "root-dir/foo.txt", "root-dir/bar", "root-dir/其他文字.docx",
+		"root-dir/sub-dir", "root-dir/sub-dir/buzz.log")
+
+	// Test Archive Extraction
+	downloadDir := filepath.Join(dir, "test-download")
+	must.Do(os.MkdirAll(downloadDir, 0644))
+
+	// success first time
+	err = ExtractCompressedDir(readerFromFile(tarPath), downloadDir, SkipOnExist)
+	must.Do(err)
+	// fail second time, due to SkipOnExist
+	err = ExtractCompressedDir(readerFromFile(tarPath), downloadDir, SkipOnExist)
+	equalErrorPrefix(err, "refusing to overwrite directory:")
+	// success again, due to OverwriteExisting
+	err = ExtractCompressedDir(readerFromFile(tarPath), downloadDir, OverwriteExisting)
+	must.Do(err)
+
+	checkDirectory(downloadDir, "root-dir")
+	checkDirectory(filepath.Join(downloadDir, "root-dir"), "foo.txt", "bar", "其他文字.docx", "sub-dir")
+	checkDirectory(filepath.Join(downloadDir, "root-dir/sub-dir"), "buzz.log")
+
+	// success twice, due to CreateNumberedFiles
+	err = ExtractCompressedDir(readerFromFile(tarPath), downloadDir, CreateNumberedFiles)
+	must.Do(err)
+	err = ExtractCompressedDir(readerFromFile(tarPath), downloadDir, CreateNumberedFiles)
+	must.Do(err)
+
+	checkDirectory(downloadDir, "root-dir", "root-dir (1)", "root-dir (2)")
+	checkDirectory(filepath.Join(downloadDir, "root-dir (2)"), "foo.txt", "bar", "其他文字.docx", "sub-dir")
+	checkDirectory(filepath.Join(downloadDir, "root-dir (2)/sub-dir"), "buzz.log")
+}