internal/fileio: extract low-level file I/O from internal/fs

Move TempFile and PreallocateFile into internal/fileio. internal/fs
primarily focuses on converting between data.Node and the actual
filesystem state. Extract the two methods to not pull in unnecessary
dependencies.

internal/backend/local/local.go

@@ -16,7 +16,7 @@ import (
 	"github.com/restic/restic/internal/backend/util"
 	"github.com/restic/restic/internal/debug"
 	"github.com/restic/restic/internal/errors"
-	"github.com/restic/restic/internal/fs"
+	"github.com/restic/restic/internal/fileio"
 
 	"github.com/cenkalti/backoff/v4"
 )
@@ -151,7 +151,7 @@ func (b *Local) Save(_ context.Context, h backend.Handle, rd backend.RewindReade
 
 	// preallocate disk space
 	if size := rd.Length(); size > 0 {
-		if err := fs.PreallocateFile(f, size); err != nil {
+		if err := fileio.PreallocateFile(f, size); err != nil {
 			debug.Log("Failed to preallocate %v with size %v: %v", finalname, size, err)
 		}
 	}

internal/fileio/file_unix.go

@@ -0,0 +1,22 @@
+//go:build !windows
+
+package fileio
+
+import (
+	"os"
+)
+
+// TempFile creates a temporary file which has already been deleted (on
+// supported platforms)
+func TempFile(dir, prefix string) (f *os.File, err error) {
+	f, err = os.CreateTemp(dir, prefix)
+	if err != nil {
+		return nil, err
+	}
+
+	if err = os.Remove(f.Name()); err != nil {
+		return nil, err
+	}
+
+	return f, nil
+}

internal/fileio/file_windows.go

@@ -0,0 +1,60 @@
+package fileio
+
+import (
+	"math/rand"
+	"os"
+	"path/filepath"
+	"strconv"
+	"syscall"
+
+	"golang.org/x/sys/windows"
+)
+
+// TempFile creates a temporary file which is marked as delete-on-close
+func TempFile(dir, prefix string) (f *os.File, err error) {
+	// slightly modified implementation of os.CreateTemp(dir, prefix) to allow us to add
+	// the FILE_ATTRIBUTE_TEMPORARY | FILE_FLAG_DELETE_ON_CLOSE flags.
+	// These provide two large benefits:
+	// FILE_ATTRIBUTE_TEMPORARY tells Windows to keep the file in memory only if possible
+	// which reduces the amount of unnecessary disk writes.
+	// FILE_FLAG_DELETE_ON_CLOSE instructs Windows to automatically delete the file once
+	// all file descriptors are closed.
+
+	if dir == "" {
+		dir = os.TempDir()
+	}
+
+	access := uint32(windows.GENERIC_READ | windows.GENERIC_WRITE)
+	creation := uint32(windows.CREATE_NEW)
+	share := uint32(0) // prevent other processes from accessing the file
+	flags := uint32(windows.FILE_ATTRIBUTE_TEMPORARY | windows.FILE_FLAG_DELETE_ON_CLOSE)
+
+	for i := 0; i < 10000; i++ {
+		randSuffix := strconv.Itoa(int(1e9 + rand.Intn(1e9)%1e9))[1:]
+		path := filepath.Join(dir, prefix+randSuffix)
+
+		ptr, err := windows.UTF16PtrFromString(path)
+		if err != nil {
+			return nil, err
+		}
+		h, err := windows.CreateFile(ptr, access, share, nil, creation, flags, 0)
+		if os.IsExist(err) {
+			continue
+		}
+		// Access denied error can occur if the tmp files conflict with each other.
+		if isAccessDeniedError(err) {
+			continue
+		}
+		return os.NewFile(uintptr(h), path), err
+	}
+
+	// Proper error handling is still to do
+	return nil, os.ErrExist
+}
+
+func isAccessDeniedError(err error) bool {
+	if errno, ok := err.(syscall.Errno); ok {
+		return errno == windows.ERROR_ACCESS_DENIED
+	}
+	return false
+}

internal/fileio/file_windows_test.go

@@ -1,21 +1,21 @@
-package fs_test
+package fileio_test
 
 import (
 	"errors"
 	"os"
 	"testing"
 
-	"github.com/restic/restic/internal/fs"
+	"github.com/restic/restic/internal/fileio"
 	rtest "github.com/restic/restic/internal/test"
 )
 
 func TestTempFile(t *testing.T) {
 	// create two temp files at the same time to check that the
 	// collision avoidance works
-	f, err := fs.TempFile("", "test")
+	f, err := fileio.TempFile("", "test")
 	fn := f.Name()
 	rtest.OK(t, err)
-	f2, err := fs.TempFile("", "test")
+	f2, err := fileio.TempFile("", "test")
 	fn2 := f2.Name()
 	rtest.OK(t, err)
 	rtest.Assert(t, fn != fn2, "filenames don't differ %s", fn)

internal/fileio/preallocate_darwin.go

@@ -1,4 +1,4 @@
-package fs
+package fileio
 
 import (
 	"os"

internal/fileio/preallocate_linux.go

@@ -1,4 +1,4 @@
-package fs
+package fileio
 
 import (
 	"os"

internal/fileio/preallocate_other.go

@@ -1,6 +1,6 @@
 //go:build !linux && !darwin
 
-package fs
+package fileio
 
 import "os"
 

internal/fileio/preallocate_test.go

@@ -1,4 +1,4 @@
-package fs
+package fileio
 
 import (
 	"os"
@@ -7,6 +7,7 @@ import (
 	"syscall"
 	"testing"
 
+	"github.com/restic/restic/internal/fs"
 	"github.com/restic/restic/internal/test"
 )
 
@@ -31,7 +32,7 @@ func TestPreallocate(t *testing.T) {
 			fi, err := wr.Stat()
 			test.OK(t, err)
 
-			efi := ExtendedStat(fi)
+			efi := fs.ExtendedStat(fi)
 			test.Assert(t, efi.Size == i || efi.Blocks > 0, "Preallocated size of %v, got size %v block %v", i, efi.Size, efi.Blocks)
 		})
 	}

internal/fs/file_unix.go

@@ -13,21 +13,6 @@ func fixpath(name string) string {
 	return name
 }
 
-// TempFile creates a temporary file which has already been deleted (on
-// supported platforms)
-func TempFile(dir, prefix string) (f *os.File, err error) {
-	f, err = os.CreateTemp(dir, prefix)
-	if err != nil {
-		return nil, err
-	}
-
-	if err = os.Remove(f.Name()); err != nil {
-		return nil, err
-	}
-
-	return f, nil
-}
-
 // isNotSupported returns true if the error is caused by an unsupported file system feature.
 func isNotSupported(err error) bool {
 	if perr, ok := err.(*os.PathError); ok && perr.Err == syscall.ENOTSUP {

internal/fs/file_windows.go

@@ -1,10 +1,8 @@
 package fs
 
 import (
-	"math/rand"
 	"os"
 	"path/filepath"
-	"strconv"
 	"strings"
 
 	"github.com/restic/restic/internal/data"
@@ -43,48 +41,6 @@ func fixpath(name string) string {
 	return name
 }
 
-// TempFile creates a temporary file which is marked as delete-on-close
-func TempFile(dir, prefix string) (f *os.File, err error) {
-	// slightly modified implementation of os.CreateTemp(dir, prefix) to allow us to add
-	// the FILE_ATTRIBUTE_TEMPORARY | FILE_FLAG_DELETE_ON_CLOSE flags.
-	// These provide two large benefits:
-	// FILE_ATTRIBUTE_TEMPORARY tells Windows to keep the file in memory only if possible
-	// which reduces the amount of unnecessary disk writes.
-	// FILE_FLAG_DELETE_ON_CLOSE instructs Windows to automatically delete the file once
-	// all file descriptors are closed.
-
-	if dir == "" {
-		dir = os.TempDir()
-	}
-
-	access := uint32(windows.GENERIC_READ | windows.GENERIC_WRITE)
-	creation := uint32(windows.CREATE_NEW)
-	share := uint32(0) // prevent other processes from accessing the file
-	flags := uint32(windows.FILE_ATTRIBUTE_TEMPORARY | windows.FILE_FLAG_DELETE_ON_CLOSE)
-
-	for i := 0; i < 10000; i++ {
-		randSuffix := strconv.Itoa(int(1e9 + rand.Intn(1e9)%1e9))[1:]
-		path := filepath.Join(dir, prefix+randSuffix)
-
-		ptr, err := windows.UTF16PtrFromString(path)
-		if err != nil {
-			return nil, err
-		}
-		h, err := windows.CreateFile(ptr, access, share, nil, creation, flags, 0)
-		if os.IsExist(err) {
-			continue
-		}
-		// Access denied error can occur if the tmp files conflict with each other.
-		if isAccessDeniedError(err) {
-			continue
-		}
-		return os.NewFile(uintptr(h), path), err
-	}
-
-	// Proper error handling is still to do
-	return nil, os.ErrExist
-}
-
 // Chmod changes the mode of the named file to mode.
 func chmod(name string, mode os.FileMode) error {
 	return os.Chmod(fixpath(name), mode)

internal/repository/packer_manager.go

@@ -16,7 +16,7 @@ import (
 	"github.com/restic/restic/internal/restic"
 
 	"github.com/restic/restic/internal/debug"
-	"github.com/restic/restic/internal/fs"
+	"github.com/restic/restic/internal/fileio"
 	"github.com/restic/restic/internal/repository/crypto"
 	"github.com/restic/restic/internal/repository/pack"
 )
@@ -201,7 +201,7 @@ func (r *packerManager) forgetPacker(packer *packer) {
 // created or one is returned that already has some blobs.
 func (r *packerManager) newPacker() (pck *packer, err error) {
 	debug.Log("create new pack")
-	tmpfile, err := fs.TempFile("", "restic-temp-pack-")
+	tmpfile, err := fileio.TempFile("", "restic-temp-pack-")
 	if err != nil {
 		return nil, errors.WithStack(err)
 	}

internal/restorer/fileswriter.go

@@ -10,6 +10,7 @@ import (
 	"github.com/hashicorp/golang-lru/v2/simplelru"
 	"github.com/restic/restic/internal/debug"
 	"github.com/restic/restic/internal/errors"
+	"github.com/restic/restic/internal/fileio"
 	"github.com/restic/restic/internal/fs"
 )
 
@@ -166,7 +167,7 @@ func ensureSize(f *os.File, fi os.FileInfo, createSize int64, sparse bool) (*os.
 			return nil, err
 		}
 	} else if createSize > 0 {
-		err := fs.PreallocateFile(f, createSize)
+		err := fileio.PreallocateFile(f, createSize)
 		if err != nil {
 			// Just log the preallocate error but don't let it cause the restore process to fail.
 			// Preallocate might return an error if the filesystem (implementation) does not