More work on diff xmit, not finished yet

luprex/core/cpp/streambuffer.hpp

@@ -338,7 +338,7 @@ public:
     void overwrite_uint32(int64_t write_count_after, uint64_t v);
     void overwrite_uint64(int64_t write_count_after, uint64_t v);
 
-    // Return true if the buffer is empty.
+    // This function checks to see if the buffer is empty.
     bool at_eof();
 
     // Verify that the buffer is empty, if not, throw StreamCorruption.
@@ -350,6 +350,9 @@ public:
     // Rewind the write cursor to a previous position.
     void unwrite_to(int64_t total_writes);
     
+    // Copy the entire contents of this streambuffer into another one.
+    void copy_into(StreamBuffer *sb);
+
     // Calculate a noncryptographic but good hash of what's in the buffer.
     util::HashValue hash() const;