Merge pull request #4163 from MichaelEischer/fix-windows-self-upgrade

self-upgrade: Fix handling of `--output` on windows

changelog/unreleased/pull-4163

@@ -0,0 +1,12 @@
+Bugfix: Repair `self-update --output new-file.exe` on Windows
+
+Since restic 0.14.0 `self-update` did not work when a custom output filename
+was specified via the `--output` option. This has been fixed.
+
+As a workaround either use an older restic version to run the self-update or
+create an empty file with the output filename before updating e.g. using CMD:
+`type nul > new-file.exe`
+`restic self-update --output new-file.exe`
+
+https://github.com/restic/restic/pull/4163
+https://forum.restic.net/t/self-update-windows-started-failing-after-release-of-0-15/5836

internal/selfupdate/download_test.go

@@ -0,0 +1,44 @@
+package selfupdate
+
+import (
+	"archive/zip"
+	"bytes"
+	"os"
+	"path/filepath"
+	"testing"
+
+	rtest "github.com/restic/restic/internal/test"
+)
+
+func TestExtractToFileZip(t *testing.T) {
+	printf := func(string, ...interface{}) {}
+	dir := t.TempDir()
+
+	ext := "zip"
+	data := []byte("Hello World!")
+
+	// create dummy archive
+	var archive bytes.Buffer
+	zw := zip.NewWriter(&archive)
+	w, err := zw.CreateHeader(&zip.FileHeader{
+		Name:               "example.exe",
+		UncompressedSize64: uint64(len(data)),
+	})
+	rtest.OK(t, err)
+	_, err = w.Write(data[:])
+	rtest.OK(t, err)
+	rtest.OK(t, zw.Close())
+
+	// run twice to test creating a new file and overwriting
+	for i := 0; i < 2; i++ {
+		outfn := filepath.Join(dir, ext+"-out")
+		rtest.OK(t, extractToFile(archive.Bytes(), "src."+ext, outfn, printf))
+
+		outdata, err := os.ReadFile(outfn)
+		rtest.OK(t, err)
+		rtest.Assert(t, bytes.Equal(data[:], outdata), "%v contains wrong data", outfn)
+
+		// overwrite to test the file is properly overwritten
+		rtest.OK(t, os.WriteFile(outfn, []byte{1, 2, 3}, 0))
+	}
+}

internal/selfupdate/download_windows.go

@@ -7,11 +7,18 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+
+	"github.com/restic/restic/internal/errors"
 )
 
 // Rename (rather than remove) the running version. The running binary will be locked
 // on Windows and cannot be removed while still executing.
 func removeResticBinary(dir, target string) error {
+	// nothing to do if the target does not exist
+	if _, err := os.Stat(target); errors.Is(err, os.ErrNotExist) {
+		return nil
+	}
+
 	backup := filepath.Join(dir, filepath.Base(target)+".bak")
 	if _, err := os.Stat(backup); err == nil {
 		_ = os.Remove(backup)