backend: move LimitReadCloser to util package

The helper is only intended for usage by backend implementations.

internal/backend/local/local.go

@@ -247,7 +247,7 @@ func (b *Local) openReader(_ context.Context, h backend.Handle, length int, offs
 	}
 
 	if length > 0 {
-		return backend.LimitReadCloser(f, int64(length)), nil
+		return util.LimitReadCloser(f, int64(length)), nil
 	}
 
 	return f, nil

internal/backend/sftp/sftp.go

@@ -437,7 +437,7 @@ func (r *SFTP) Load(ctx context.Context, h backend.Handle, length int, offset in
 
 		// check the underlying reader to be agnostic to however fn() handles the returned error
 		_, rderr := rd.Read([]byte{0})
-		if rderr == io.EOF && rd.(*backend.LimitedReadCloser).N != 0 {
+		if rderr == io.EOF && rd.(*util.LimitedReadCloser).N != 0 {
 			// file is too short
 			return fmt.Errorf("%w: %v", errTooShort, err)
 		}
@@ -463,7 +463,7 @@ func (r *SFTP) openReader(_ context.Context, h backend.Handle, length int, offse
 	if length > 0 {
 		// unlimited reads usually use io.Copy which needs WriteTo support at the underlying reader
 		// limited reads are usually combined with io.ReadFull which reads all required bytes into a buffer in one go
-		return backend.LimitReadCloser(f, int64(length)), nil
+		return util.LimitReadCloser(f, int64(length)), nil
 	}
 
 	return f, nil

internal/backend/util/limited_reader.go

@@ -0,0 +1,15 @@
+package util
+
+import "io"
+
+// LimitedReadCloser wraps io.LimitedReader and exposes the Close() method.
+type LimitedReadCloser struct {
+	io.Closer
+	io.LimitedReader
+}
+
+// LimitReadCloser returns a new reader wraps r in an io.LimitedReader, but also
+// exposes the Close() method.
+func LimitReadCloser(r io.ReadCloser, n int64) *LimitedReadCloser {
+	return &LimitedReadCloser{Closer: r, LimitedReader: io.LimitedReader{R: r, N: n}}
+}

internal/backend/utils.go

@@ -62,15 +62,3 @@ func LoadAll(ctx context.Context, buf []byte, be Backend, h Handle) ([]byte, err
 
 	return buf, nil
 }
-
-// LimitedReadCloser wraps io.LimitedReader and exposes the Close() method.
-type LimitedReadCloser struct {
-	io.Closer
-	io.LimitedReader
-}
-
-// LimitReadCloser returns a new reader wraps r in an io.LimitedReader, but also
-// exposes the Close() method.
-func LimitReadCloser(r io.ReadCloser, n int64) *LimitedReadCloser {
-	return &LimitedReadCloser{Closer: r, LimitedReader: io.LimitedReader{R: r, N: n}}
-}