Create common base classes for buffered streams

Most streams are backed by a memory buffer. Create common base classes
for this functionality to avoid code duplication.

common/rdr/BufferedInStream.h

@@ -0,0 +1,54 @@
+/* Copyright (C) 2002-2005 RealVNC Ltd.  All Rights Reserved.
+ * Copyright 2020 Pierre Ossman for Cendio AB
+ * 
+ * This is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ * 
+ * This software is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this software; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307,
+ * USA.
+ */
+
+//
+// Base class for input streams with a buffer
+//
+
+#ifndef __RDR_BUFFEREDINSTREAM_H__
+#define __RDR_BUFFEREDINSTREAM_H__
+
+#include <rdr/InStream.h>
+
+namespace rdr {
+
+  class BufferedInStream : public InStream {
+
+  public:
+    virtual ~BufferedInStream();
+
+    virtual size_t pos();
+
+  private:
+    virtual bool fillBuffer(size_t maxSize, bool wait) = 0;
+
+    virtual size_t overrun(size_t itemSize, size_t nItems, bool wait);
+
+  private:
+    size_t bufSize;
+    size_t offset;
+    U8* start;
+
+  protected:
+    BufferedInStream(size_t bufSize=0);
+  };
+
+} // end of namespace rdr
+
+#endif