Merge pull request #44 from taruti/taruti/file-locking

Add support for file locking

Author: mcuadros

fs.go

@@ -135,4 +135,9 @@ type File interface {
 	io.ReaderAt
 	io.Seeker
 	io.Closer
+	// Lock locks the file like e.g. flock. It protects against access from
+	// other processes.
+	Lock() error
+	// Unlock unlocks the file.
+	Unlock() error
 }

memfs/memory.go

@@ -297,6 +297,15 @@ func (f *file) Stat() (os.FileInfo, error) {
 	}, nil
 }
 
+// Lock protects file from access from other processes. Which is a no-op
+// for this memory only filesystem.
+func (f *file) Lock() error {
+	return nil
+}
+func (f *file) Unlock() error {
+	return nil
+}
+
 type fileInfo struct {
 	name string
 	size int

osfs/os.go

@@ -23,6 +23,11 @@ func New(baseDir string) billy.Filesystem {
 	return chroot.New(&OS{}, baseDir)
 }
 
+// file is a wrapper for an os.File which adds support for file locking.
+type file struct {
+	*os.File
+}
+
 func (fs *OS) Create(filename string) (billy.File, error) {
 	return fs.OpenFile(filename, os.O_RDWR|os.O_CREATE|os.O_TRUNC, defaultCreateMode)
 }
@@ -34,7 +39,11 @@ func (fs *OS) OpenFile(filename string, flag int, perm os.FileMode) (billy.File,
 		}
 	}
 
-	return os.OpenFile(filename, flag, perm)
+	f, err := os.OpenFile(filename, flag, perm)
+	if err != nil {
+		return nil, err
+	}
+	return file{f}, err
 }
 
 func (fs *OS) createDir(fullpath string) error {
@@ -87,7 +96,11 @@ func (fs *OS) TempFile(dir, prefix string) (billy.File, error) {
 		return nil, err
 	}
 
-	return ioutil.TempFile(dir, prefix)
+	f, err := ioutil.TempFile(dir, prefix)
+	if err != nil {
+		return nil, err
+	}
+	return file{f}, nil
 }
 
 func (fs *OS) Join(elem ...string) string {

osfs/os_posix.go

@@ -4,9 +4,18 @@ package osfs
 
 import (
 	"os"
+	"syscall"
 )
 
 // Stat returns the FileInfo structure describing file.
 func (fs *OS) Stat(filename string) (os.FileInfo, error) {
 	return os.Stat(filename)
 }
+
+// Lock protects file from access from other processes.
+func (f file) Lock() error {
+	return syscall.Flock(int(f.File.Fd()), syscall.LOCK_EX)
+}
+func (f file) Unlock() error {
+	return syscall.Flock(int(f.File.Fd()), syscall.LOCK_UN)
+}

osfs/os_windows.go

@@ -5,7 +5,11 @@ package osfs
 import (
 	"os"
 	"path/filepath"
+	"runtime"
 	"strings"
+	"unsafe"
+
+	"golang.org/x/sys/windows"
 )
 
 // Stat returns the FileInfo structure describing file.
@@ -39,3 +43,34 @@ type fileInfo struct {
 func (fi *fileInfo) Name() string {
 	return fi.name
 }
+
+var (
+	kernel32DLL    = windows.NewLazySystemDLL("kernel32.dll")
+	lockFileExProc = kernel32DLL.NewProc("LockFileEx")
+	unlockFileProc = kernel32DLL.NewProc("UnlockFile")
+)
+
+const (
+	lockfileExclusiveLock = 0x2
+)
+
+// Lock protects file from access from other processes.
+func (f file) Lock() error {
+	var overlapped windows.Overlapped
+	// err is always non-nil as per sys/windows semantics.
+	ret, _, err := lockFileExProc.Call(f.File.Fd(), lockfileExclusiveLock, 0, 0xFFFFFFFF, 0,
+		uintptr(unsafe.Pointer(&overlapped)))
+	runtime.KeepAlive(&overlapped)
+	if ret == 0 {
+		return err
+	}
+	return nil
+}
+func (f file) Unlock() error {
+	// err is always non-nil as per sys/windows semantics.
+	ret, _, err := unlockFileProc.Call(f.File.Fd(), 0, 0, 0xFFFFFFFF, 0)
+	if ret == 0 {
+		return err
+	}
+	return nil
+}

test/mock.go

@@ -122,3 +122,11 @@ func (*FileMock) Seek(offset int64, whence int) (int64, error) {
 func (*FileMock) Close() error {
 	return nil
 }
+
+func (*FileMock) Lock() error {
+	return nil
+}
+
+func (*FileMock) Unlock() error {
+	return nil
+}