[PoC] copy on write

all_test.go

@@ -11,6 +11,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/otiai10/copy/plugins/copyonwrite"
 	. "github.com/otiai10/mint"
 )
 
@@ -476,3 +477,15 @@ func TestOptions_RenameDestination(t *testing.T) {
 	_, err = os.Stat("test/data.copy/case20/foo/control.txt")
 	Expect(t, err).ToBe(nil)
 }
+
+func TestOptions_FileCopyFunc_OnMacOS(t *testing.T) {
+	if runtime.GOOS != "darwin" {
+		t.Skip("This test is only for macOS")
+	}
+	// You can use your own file copy function
+	opt := Options{
+		FileCopyFunc: copyonwrite.CopyOnWrite,
+	}
+	err := Copy("test/data/case21", "test/data.copy/case21", opt)
+	Expect(t, err).ToBe(nil)
+}

copy.go

@@ -87,6 +87,46 @@ func copyNextOrSkip(src, dest string, info os.FileInfo, opt Options) error {
 // and file permission.
 func fcopy(src, dest string, info os.FileInfo, opt Options) (err error) {
 
+	if err = os.MkdirAll(filepath.Dir(dest), os.ModePerm); err != nil {
+		return
+	}
+
+	if opt.FileCopyFunc != nil {
+		if err = opt.FileCopyFunc(src, dest); err != nil {
+			return err
+		}
+	} else {
+		if err = fcopyByReadAndWrite(src, dest, info, opt); err != nil {
+			return err
+		}
+	}
+
+	chmodfunc, err := opt.PermissionControl(info, dest)
+	if err != nil {
+		return err
+	}
+	chmodfunc(&err)
+	if os.IsNotExist(err) {
+		// See https://github.com/otiai10/copy/issues/72
+		// Gracefully handle files/symlinks/dirs deleted while copy
+		return nil
+	}
+
+	if opt.PreserveOwner {
+		if err := preserveOwner(src, dest, info); err != nil {
+			return err
+		}
+	}
+	if opt.PreserveTimes {
+		if err := preserveTimes(info, dest); err != nil {
+			return err
+		}
+	}
+
+	return
+}
+
+func fcopyByReadAndWrite(src, dest string, info os.FileInfo, opt Options) (err error) {
 	var readcloser io.ReadCloser
 	if opt.FS != nil {
 		readcloser, err = opt.FS.Open(src)
@@ -101,22 +141,12 @@ func fcopy(src, dest string, info os.FileInfo, opt Options) (err error) {
 	}
 	defer fclose(readcloser, &err)
 
-	if err = os.MkdirAll(filepath.Dir(dest), os.ModePerm); err != nil {
-		return
-	}
-
 	f, err := os.Create(dest)
 	if err != nil {
 		return
 	}
 	defer fclose(f, &err)
 
-	chmodfunc, err := opt.PermissionControl(info, dest)
-	if err != nil {
-		return err
-	}
-	chmodfunc(&err)
-
 	var buf []byte = nil
 	var w io.Writer = f
 	var r io.Reader = readcloser
@@ -141,18 +171,7 @@ func fcopy(src, dest string, info os.FileInfo, opt Options) (err error) {
 		err = f.Sync()
 	}
 
-	if opt.PreserveOwner {
-		if err := preserveOwner(src, dest, info); err != nil {
-			return err
-		}
-	}
-	if opt.PreserveTimes {
-		if err := preserveTimes(info, dest); err != nil {
-			return err
-		}
-	}
-
-	return
+	return err
 }
 
 // dcopy is for a directory,

options.go

@@ -71,6 +71,11 @@ type Options struct {
 	// e.g., You can use embed.FS to copy files from embedded filesystem.
 	FS fs.FS
 
+	// FileCopyFunc is a function to copy an actual file.
+	// If nil, it uses the default file copying function with `io.Copy`.
+	// e.g., You can use `CopyOnWrite` to copy files with copy-on-write.
+	FileCopyFunc func(src, dest string) error
+
 	// NumOfWorkers represents the number of workers used for
 	// concurrent copying contents of directories.
 	// If 0 or 1, it does not use goroutine for copying directories.

plugins/copyonwrite/README.md

@@ -0,0 +1,3 @@
+# Support CopyOnWrite of macOS
+
+// TODO: Write more description

plugins/copyonwrite/copyonwrite_darwin copy.go

@@ -0,0 +1,9 @@
+//go:build darwin
+
+package copyonwrite
+
+import "golang.org/x/sys/unix"
+
+func CopyOnWrite(src, dst string) error {
+	return unix.Clonefile(src, dst, 0)
+}

plugins/copyonwrite/copyonwrite_x.go

@@ -0,0 +1,9 @@
+//go:build !darwin
+
+package copyonwrite
+
+import "errors"
+
+func CopyOnWrite(src, dst string) error {
+	return errors.New("copy-on-write is not supported on this platform")
+}

test/data/case21/README.md

@@ -0,0 +1 @@
+# CopyOnWrite plugin