1 files changed, 66 insertions, 0 deletions
diff --git a/internal/lockedfile/lockedfile_filelock.go b/internal/lockedfile/lockedfile_filelock.go
new file mode 100644
index 000000000..7c71672c8
--- /dev/null
+++ b/internal/lockedfile/lockedfile_filelock.go
@@ -0,0 +1,66 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build !plan9
+// +build !plan9
+
+package lockedfile
+
+import (
+	"io/fs"
+	"os"
+
+	"golang.org/x/tools/internal/lockedfile/internal/filelock"
+)
+
+func openFile(name string, flag int, perm fs.FileMode) (*os.File, error) {
+	// On BSD systems, we could add the O_SHLOCK or O_EXLOCK flag to the OpenFile
+	// call instead of locking separately, but we have to support separate locking
+	// calls for Linux and Windows anyway, so it's simpler to use that approach
+	// consistently.
+
+	f, err := os.OpenFile(name, flag&^os.O_TRUNC, perm)
+	if err != nil {
+		return nil, err
+	}
+
+	switch flag & (os.O_RDONLY | os.O_WRONLY | os.O_RDWR) {
+	case os.O_WRONLY, os.O_RDWR:
+		err = filelock.Lock(f)
+	default:
+		err = filelock.RLock(f)
+	}
+	if err != nil {
+		f.Close()
+		return nil, err
+	}
+
+	if flag&os.O_TRUNC == os.O_TRUNC {
+		if err := f.Truncate(0); err != nil {
+			// The documentation for os.O_TRUNC says “if possible, truncate file when
+			// opened”, but doesn't define “possible” (golang.org/issue/28699).
+			// We'll treat regular files (and symlinks to regular files) as “possible”
+			// and ignore errors for the rest.
+			if fi, statErr := f.Stat(); statErr != nil || fi.Mode().IsRegular() {
+				filelock.Unlock(f)
+				f.Close()
+				return nil, err
+			}
+		}
+	}
+
+	return f, nil
+}
+
+func closeFile(f *os.File) error {
+	// Since locking syscalls operate on file descriptors, we must unlock the file
+	// while the descriptor is still valid — that is, before the file is closed —
+	// and avoid unlocking files that are already closed.
+	err := filelock.Unlock(f)
+
+	if closeErr := f.Close(); err == nil {
+		err = closeErr
+	}
+	return err
+}