fix(libindex): temp files on non-linux

Signed-off-by: RTann <rtannenb@redhat.com>

libindex/fetcher.go

@@ -21,7 +21,6 @@ import (
 	"go.opentelemetry.io/otel/trace"
 	"golang.org/x/sync/errgroup"
 	"golang.org/x/sync/singleflight"
-	"golang.org/x/sys/unix"
 
 	"github.com/quay/claircore"
 	"github.com/quay/claircore/indexer"
@@ -66,13 +65,13 @@ func NewRemoteFetchArena(wc *http.Client, root string) *RemoteFetchArena {
 // Rc is a reference counter.
 type rc struct {
 	sync.Mutex
-	val   *os.File
+	val   *tempFile
 	count int
 	done  func()
 }
 
 // NewRc makes an rc.
-func newRc(v *os.File, done func()) *rc {
+func newRc(v *tempFile, done func()) *rc {
 	return &rc{
 		val:  v,
 		done: done,
@@ -115,15 +114,7 @@ type ref struct {
 func (r *ref) Val() (*os.File, error) {
 	r.rc.Lock()
 	defer r.rc.Unlock()
-	fd := int(r.rc.val.Fd())
-	if fd == -1 {
-		return nil, errStale
-	}
-	p := fmt.Sprintf(`/proc/self/fd/%d`, fd)
-	// Need to use OpenFile so that the symlink is not dereferenced.
-	// There's some proc magic so that opening that symlink itself copies the
-	// description.
-	return os.OpenFile(p, os.O_RDONLY, 0644)
+	return r.rc.val.Reopen()
 }
 
 // Close decrements the refcount.
@@ -250,7 +241,7 @@ func (a *RemoteFetchArena) fetchUnlinkedFile(ctx context.Context, key string, de
 		return v.(*rc), nil
 	}
 	// Otherwise, it needs to be populated.
-	f, err := os.OpenFile(a.root, os.O_WRONLY|unix.O_TMPFILE, 0644)
+	f, err := openTemp(a.root)
 	if err != nil {
 		return nil, err
 	}

libindex/tempfile_linux.go

@@ -0,0 +1,31 @@
+package libindex
+
+import (
+	"fmt"
+	"os"
+
+	"golang.org/x/sys/unix"
+)
+
+type tempFile struct {
+	*os.File
+}
+
+func openTemp(dir string) (*tempFile, error) {
+	f, err := os.OpenFile(dir, os.O_WRONLY|unix.O_TMPFILE, 0644)
+	if err != nil {
+		return nil, err
+	}
+	return &tempFile{
+		File: f,
+	}, nil
+}
+
+func (t *tempFile) Reopen() (*os.File, error) {
+	fd := int(t.Fd())
+	if fd == -1 {
+		return nil, errStale
+	}
+	p := fmt.Sprintf("/proc/self/fd/%d", fd)
+	return os.OpenFile(p, os.O_RDONLY, 0644)
+}

libindex/tempfile_unix.go

@@ -0,0 +1,30 @@
+//go:build unix && !linux
+
+package libindex
+
+import (
+	"errors"
+	"os"
+)
+
+type tempFile struct {
+	*os.File
+}
+
+func openTemp(dir string) (*tempFile, error) {
+	f, err := os.CreateTemp(dir, "*.fetch")
+	if err != nil {
+		return nil, err
+	}
+	return &tempFile{
+		File: f,
+	}, nil
+}
+
+func (t *tempFile) Reopen() (*os.File, error) {
+	return os.OpenFile(t.Name(), os.O_RDONLY, 0644)
+}
+
+func (t *tempFile) Close() error {
+	return errors.Join(os.Remove(t.Name()), t.File.Close())
+}

libindex/tempfile_windows.go

@@ -0,0 +1,43 @@
+package libindex
+
+import (
+	"errors"
+	"fmt"
+	"io/fs"
+	"os"
+	"path/filepath"
+	_ "unsafe" // linker tricks
+)
+
+// This is a very rough port of src/os/tempfile.go that adds the magic
+// autodelete flag.
+
+//go:linkname fastrand runtime.fastrand
+func fastrand() uint32
+
+type tempFile struct {
+	*os.File
+}
+
+func openTemp(dir string) (*tempFile, error) {
+	// Copied out of golang.org/x/sys/windows
+	const FILE_FLAG_DELETE_ON_CLOSE = 0x04000000
+	for {
+		fn := fmt.Sprintf("fetch.%d", fastrand())
+		f, err := os.OpenFile(filepath.Join(dir, fn), os.O_WRONLY|FILE_FLAG_DELETE_ON_CLOSE, 0644)
+		switch {
+		case errors.Is(err, nil):
+			return &tempFile{
+				File: f,
+			}, nil
+		case errors.Is(err, fs.ErrExist):
+			// Continue
+		default:
+			return nil, err
+		}
+	}
+}
+
+func (t *tempFile) Reopen() (*os.File, error) {
+	return os.OpenFile(t.Name(), os.O_RDONLY, 0644)
+}