Merge pull request #18015 from ghalliday/issue30005bug

HPCC-30798 Fix potential internal error when large rows serialised in roxie

Reviewed-by: Mark Kelly mark.kelly@lexisnexisrisk.com
Merged-by: Gavin Halliday <ghalliday@hpccsystems.com>

roxie/udplib/udptrs.cpp

@@ -1338,6 +1338,11 @@ class CMessagePacker : implements IMessagePacker, public CInterface
         }
         else
         {
+            //Edge case - ensure that the length of a variable length record does not span a packet
+            //this can occur when large rows > data_buffer_size are being appended to the buffer.
+            if (variable && ((data_buffer_size - data_used) < sizeof(RecordLengthType)))
+                flush(false);
+
             while (len)
             {
                 if (!part_buffer)