refactor: Split common code out of CopyBytes

Permission changes, ownership preservation, and access/modify/creation
time presevation is something all implementations need. I brought it
out of the CopyBytes implementation so it can be shared when more
implementations are added later.

A small note:

The "ignore if source file deleted" check had to be brought out of
`CopyBytes`. The way it worked before is it returned no error, which
meant `fcopy` would try and modify the destination file (which was never
created). Instead, I check for the error explicitly in `fcopy`.

copy.go

@@ -2,6 +2,7 @@ package copy
 
 import (
 	"context"
+	"errors"
 	"io"
 	"io/fs"
 	"os"
@@ -86,7 +87,45 @@ func copyNextOrSkip(src, dest string, info os.FileInfo, opt Options) error {
 // with considering existence of parent directory
 // and file permission.
 func fcopy(src, dest string, info os.FileInfo, opt Options) (err error) {
-	return opt.FileCopyFunc.fcopy(src, dest, info, opt)
+	if err = os.MkdirAll(filepath.Dir(dest), os.ModePerm); err != nil {
+		return
+	}
+
+	// Use FileCopyMethod to do copy.
+	if err = opt.FileCopyFunc.fcopy(src, dest, info, opt); err != nil {
+		if pathError, ok := err.(*os.PathError); ok && errors.Is(err, os.ErrNotExist) && pathError.Path == src {
+			// Source file deleted. Ignore error.
+			return nil
+		}
+
+		return err
+	}
+
+	// Change file permissions.
+	chmodfunc, err := opt.PermissionControl(info, dest)
+	if err != nil {
+		return err
+	}
+
+	chmodfunc(&err)
+	if err != nil {
+		return err
+	}
+
+	// Preserve file ownership and times.
+	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
 }
 
 // dcopy is for a directory,

copy_methods.go

@@ -4,7 +4,6 @@ import (
 	"errors"
 	"io"
 	"os"
-	"path/filepath"
 )
 
 // ErrUnsupportedCopyMethod is returned when the FileCopyMethod specified in
@@ -17,37 +16,23 @@ var ErrUnsupportedCopyMethod = errors.New(
 // then writing the buffer back to the destination file.
 var CopyBytes = FileCopyMethod{
 	fcopy: func(src, dest string, info os.FileInfo, opt Options) (err error) {
-
 		var readcloser io.ReadCloser
 		if opt.FS != nil {
 			readcloser, err = opt.FS.Open(src)
 		} else {
 			readcloser, err = os.Open(src)
 		}
 		if err != nil {
-			if os.IsNotExist(err) {
-				return nil
-			}
 			return
 		}
 		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
@@ -72,17 +57,6 @@ var CopyBytes = FileCopyMethod{
 			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
 	},
 }