[core] Added restrictions on pktseq/msgno fields in srt_sendmsg2 call (…

…#1879)

srtcore/core.cpp

@@ -6288,10 +6288,17 @@ int CUDT::sendmsg2(const char *data, int len, SRT_MSGCTRL& w_mctrl)
         IF_HEAVY_LOGGING(steady_clock::time_point ts_srctime =
                              steady_clock::time_point() + microseconds_from(w_mctrl.srctime));
 
+#if ENABLE_EXPERIMENTAL_BONDING
         // Check if seqno has been set, in case when this is a group sender.
         // If the sequence is from the past towards the "next sequence",
         // simply return the size, pretending that it has been sent.
-        if (w_mctrl.pktseq != SRT_SEQNO_NONE && m_iSndNextSeqNo != SRT_SEQNO_NONE)
+
+        // NOTE: it's assumed that if this is a group member, then
+        // an attempt to call srt_sendmsg2 has been rejected, and so
+        // the pktseq field has been set by the internal group sender function.
+        if (m_parent->m_GroupOf
+                && w_mctrl.pktseq != SRT_SEQNO_NONE
+                && m_iSndNextSeqNo != SRT_SEQNO_NONE)
         {
             if (CSeqNo::seqcmp(w_mctrl.pktseq, seqno) < 0)
             {
@@ -6300,6 +6307,7 @@ int CUDT::sendmsg2(const char *data, int len, SRT_MSGCTRL& w_mctrl)
                 return size;
             }
         }
+#endif
 
         // Set this predicted next sequence to the control information.
         // It's the sequence of the FIRST (!) packet from all packets used to send