diff --git a/libretroshare/src/ft/ftchunkmap.cc b/libretroshare/src/ft/ftchunkmap.cc
new file mode 100644
index 000000000..cc8dda5c2
--- /dev/null
+++ b/libretroshare/src/ft/ftchunkmap.cc
@@ -0,0 +1,34 @@
+#include <math.h>
+#include "ftchunkmap.h"
+
+ChunkMap::ChunkMap(uint64_t s)
+{
+	file_size = s ;
+
+	chunk_size = 1024*1024 ;	// 1MB chunks
+	uint64_t n = s/chunk_size ;
+	if(s% (uint64_t)chunk_size != 0)
+		++n ;
+
+	chunks.resize(n,CHUNK_OUTSTANDING) ;
+}
+
+void ChunkMap::received(uint64_t offset)
+{
+	uint64_t n = offset/chunk_size ;
+
+	for(uint64_t i=0;i<n;++i)
+		chunks[i] = CHUNK_DONE ;
+
+	if(offset == file_size)
+		chunks.back() = CHUNK_DONE ;
+}
+
+void ChunkMap::requested(uint64_t offset, uint32_t size)
+{
+	int start = offset/chunk_size ;
+	int end = (int)ceil((offset+size)/chunk_size) ;
+
+	for(int i=start;i<=end;++i)
+		chunks[i] = CHUNK_ACTIVE ;
+}
diff --git a/libretroshare/src/ft/ftchunkmap.h b/libretroshare/src/ft/ftchunkmap.h
new file mode 100644
index 000000000..6b03ceab6
--- /dev/null
+++ b/libretroshare/src/ft/ftchunkmap.h
@@ -0,0 +1,13 @@
+#pragma once
+
+#include <rsiface/rstypes.h>
+
+class ChunkMap: public FileChunksInfo
+{
+	public:
+		ChunkMap(uint64_t size) ;
+
+		virtual void received(uint64_t offset) ;
+		virtual void requested(uint64_t offset, uint32_t chunk_size) ;
+};
+