VFS improvements.

util/vfsutil/slice.go

@@ -0,0 +1,96 @@
+package vfsutil
+
+import (
+	"io"
+
+	"github.com/ncruces/go-sqlite3"
+	"github.com/ncruces/go-sqlite3/vfs"
+)
+
+// SliceFile implements [vfs.File] with a byte slice.
+// It is suitable for temporary files (such as [vfs.OPEN_TEMP_JOURNAL]),
+// but not concurrency safe.
+type SliceFile []byte
+
+var (
+	// Ensure these interfaces are implemented:
+	_ vfs.FileSizeHint = &SliceFile{}
+)
+
+// ReadAt implements [io.ReaderAt].
+func (f *SliceFile) ReadAt(b []byte, off int64) (n int, err error) {
+	if d := *f; off < int64(len(d)) {
+		n = copy(b, d[off:])
+	}
+	if n < len(b) {
+		err = io.EOF
+	}
+	return
+}
+
+// WriteAt implements [io.WriterAt].
+func (f *SliceFile) WriteAt(b []byte, off int64) (n int, err error) {
+	d := *f
+	if off > int64(len(d)) {
+		d = append(d, make([]byte, off-int64(len(d)))...)
+	}
+	d = append(d[:off], b...)
+	if len(d) > len(*f) {
+		*f = d
+	}
+	return len(b), nil
+}
+
+// Size implements [vfs.File].
+func (f *SliceFile) Size() (int64, error) {
+	return int64(len(*f)), nil
+}
+
+// Truncate implements [vfs.File].
+func (f *SliceFile) Truncate(size int64) error {
+	if d := *f; size < int64(len(d)) {
+		*f = d[:size]
+	}
+	return nil
+}
+
+// SizeHint implements [vfs.FileSizeHint].
+func (f *SliceFile) SizeHint(size int64) error {
+	if d := *f; size > int64(len(d)) {
+		*f = append(d, make([]byte, size-int64(len(d)))...)
+	}
+	return nil
+}
+
+// Close implements [io.Closer].
+func (*SliceFile) Close() error { return nil }
+
+// Sync implements [vfs.File].
+func (*SliceFile) Sync(flags vfs.SyncFlag) error { return nil }
+
+// Lock implements [vfs.File].
+func (*SliceFile) Lock(lock vfs.LockLevel) error { return nil }
+
+// Unlock implements [vfs.File].
+func (*SliceFile) Unlock(lock vfs.LockLevel) error { return nil }
+
+// CheckReservedLock implements [vfs.File].
+func (*SliceFile) CheckReservedLock() (bool, error) {
+	// notest // OPEN_MEMORY
+	return false, sqlite3.IOERR_CHECKRESERVEDLOCK
+}
+
+// SectorSize implements [vfs.File].
+func (*SliceFile) SectorSize() int {
+	// notest // IOCAP_POWERSAFE_OVERWRITE
+	return 0
+}
+
+// DeviceCharacteristics implements [vfs.File].
+func (*SliceFile) DeviceCharacteristics() vfs.DeviceCharacteristic {
+	return vfs.IOCAP_ATOMIC |
+		vfs.IOCAP_SEQUENTIAL |
+		vfs.IOCAP_SAFE_APPEND |
+		vfs.IOCAP_POWERSAFE_OVERWRITE |
+		vfs.IOCAP_SUBPAGE_READ
+}