Add private BDataPositionIOWrapper

Implements the BPositionIO interface on top of a BDataIO, requiring the
{Read,Write}At() accesses to be sequential.

headers/private/support/DataPositionIOWrapper.h

@@ -0,0 +1,37 @@
+/*
+ * Copyright 2014, Ingo Weinhold, [email protected].
+ * Distributed under the terms of the MIT License.
+ */
+#ifndef _DATA_POSITION_IO_WRAPPER_H_
+#define _DATA_POSITION_IO_WRAPPER_H_
+
+
+#include <DataIO.h>
+
+
+class BDataPositionIOWrapper : public BPositionIO {
+public:
+								BDataPositionIOWrapper(BDataIO* io);
+								~BDataPositionIOWrapper();
+
+	virtual	ssize_t				Read(void* buffer, size_t size);
+	virtual	ssize_t				Write(const void* buffer, size_t size);
+
+	virtual	ssize_t				ReadAt(off_t position, void* buffer,
+									size_t size);
+	virtual	ssize_t				WriteAt(off_t position, const void* buffer,
+									size_t size);
+
+	virtual	off_t				Seek(off_t position, uint32 seekMode);
+	virtual	off_t				Position() const;
+
+	virtual	status_t			SetSize(off_t size);
+	virtual	status_t			GetSize(off_t* size) const;
+
+private:
+				BDataIO*		fIO;
+				off_t			fPosition;
+};
+
+
+#endif	// _DATA_POSITION_IO_WRAPPER_H_