diff --git a/rdr/ZlibOutStream.cxx b/rdr/ZlibOutStream.cxx
new file mode 100644
index 0000000..6aadde1
--- /dev/null
+++ b/rdr/ZlibOutStream.cxx
@@ -0,0 +1,140 @@
+/* Copyright (C) 2002-2004 RealVNC Ltd.  All Rights Reserved.
+ *    
+ * 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.
+ */
+
+#include <rdr/ZlibOutStream.h>
+#include <rdr/Exception.h>
+#include <zlib.h>
+
+using namespace rdr;
+
+enum { DEFAULT_BUF_SIZE = 16384 };
+
+ZlibOutStream::ZlibOutStream(OutStream* os, int bufSize_, int compressLevel)
+  : underlying(os), bufSize(bufSize_ ? bufSize_ : DEFAULT_BUF_SIZE), offset(0)
+{
+  zs = new z_stream;
+  zs->zalloc    = Z_NULL;
+  zs->zfree     = Z_NULL;
+  zs->opaque    = Z_NULL;
+  if (deflateInit(zs, compressLevel) != Z_OK) {
+    delete zs;
+    throw Exception("ZlibOutStream: deflateInit failed");
+  }
+  ptr = start = new U8[bufSize];
+  end = start + bufSize;
+}
+
+ZlibOutStream::~ZlibOutStream()
+{
+  try {
+    flush();
+  } catch (Exception&) {
+  }
+  delete [] start;
+  deflateEnd(zs);
+  delete zs;
+}
+
+void ZlibOutStream::setUnderlying(OutStream* os)
+{
+  underlying = os;
+}
+
+int ZlibOutStream::length()
+{
+  return offset + ptr - start;
+}
+
+void ZlibOutStream::flush()
+{
+  zs->next_in = start;
+  zs->avail_in = ptr - start;
+
+//    fprintf(stderr,"zos flush: avail_in %d\n",zs->avail_in);
+
+  while (zs->avail_in != 0) {
+
+    do {
+      underlying->check(1);
+      zs->next_out = underlying->getptr();
+      zs->avail_out = underlying->getend() - underlying->getptr();
+
+//        fprintf(stderr,"zos flush: calling deflate, avail_in %d, avail_out %d\n",
+//                zs->avail_in,zs->avail_out);
+      int rc = deflate(zs, Z_SYNC_FLUSH);
+      if (rc != Z_OK) throw Exception("ZlibOutStream: deflate failed");
+
+//        fprintf(stderr,"zos flush: after deflate: %d bytes\n",
+//                zs->next_out-underlying->getptr());
+
+      underlying->setptr(zs->next_out);
+    } while (zs->avail_out == 0);
+  }
+
+  offset += ptr - start;
+  ptr = start;
+}
+
+int ZlibOutStream::overrun(int itemSize, int nItems)
+{
+//    fprintf(stderr,"ZlibOutStream overrun\n");
+
+  if (itemSize > bufSize)
+    throw Exception("ZlibOutStream overrun: max itemSize exceeded");
+
+  while (end - ptr < itemSize) {
+    zs->next_in = start;
+    zs->avail_in = ptr - start;
+
+    do {
+      underlying->check(1);
+      zs->next_out = underlying->getptr();
+      zs->avail_out = underlying->getend() - underlying->getptr();
+
+//        fprintf(stderr,"zos overrun: calling deflate, avail_in %d, avail_out %d\n",
+//                zs->avail_in,zs->avail_out);
+
+      int rc = deflate(zs, 0);
+      if (rc != Z_OK) throw Exception("ZlibOutStream: deflate failed");
+
+//        fprintf(stderr,"zos overrun: after deflate: %d bytes\n",
+//                zs->next_out-underlying->getptr());
+
+      underlying->setptr(zs->next_out);
+    } while (zs->avail_out == 0);
+
+    // output buffer not full
+
+    if (zs->avail_in == 0) {
+      offset += ptr - start;
+      ptr = start;
+    } else {
+      // but didn't consume all the data?  try shifting what's left to the
+      // start of the buffer.
+      fprintf(stderr,"z out buf not full, but in data not consumed\n");
+      memmove(start, zs->next_in, ptr - zs->next_in);
+      offset += zs->next_in - start;
+      ptr -= zs->next_in - start;
+    }
+  }
+
+  if (itemSize * nItems > end - ptr)
+    nItems = (end - ptr) / itemSize;
+
+  return nItems;
+}