Merge pull request #18236 from ghalliday/issue31139_812

HPCC-31139 Length field gets corrupted in resent encrypted packets

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

roxie/udplib/udptrs.cpp

@@ -572,8 +572,9 @@ class UdpReceiverEntry : public IUdpReceiverEntry
                         const char *data = buffer->data + sizeof(UdpPacketHeader);
                         const MemoryAttr &udpkey = getSecretUdpKey(true);
                         aesEncrypt(udpkey.get(), udpkey.length(), data, length, encryptBuffer);
-                        header->length = encryptBuffer.length();
-                        encryptBuffer.writeDirect(0, sizeof(UdpPacketHeader), header);   // Only really need length updating
+                        UdpPacketHeader newHeader;
+                        newHeader.length = encryptBuffer.length();
+                        encryptBuffer.writeDirect(offsetof(UdpPacketHeader, length), sizeof(newHeader.length), &newHeader.length);  // Only need to update the length - rest is the same
                         assertex(encryptBuffer.length() <= DATA_PAYLOAD);
                         if (udpTraceLevel > 5)
                             DBGLOG("ENCRYPT: Writing %u bytes to data socket", encryptBuffer.length());