ws: ss: add tx SOM validation at SS layer

These checks exist now at wsi layer, add them at ss layer so they can
provide streamtype information about which TX is broken.

Author: lws-team

lib/secure-streams/protocols/ss-ws.c

@@ -117,8 +117,10 @@ secstream_ws(struct lws *wsi, enum lws_callback_reasons reason, void *user,
 		if (!h) {
 			return LWSSSSRET_DISCONNECT_ME;
 		}
-		h->retry = 0;
-		h->seqstate = SSSEQ_CONNECTED;
+		h->retry		= 0;
+		h->seqstate		= SSSEQ_CONNECTED;
+		wsi->ws->last_valid	= 0;
+		wsi->ws->last_fin	= 0;
 		lws_sul_cancel(&h->sul);
 #if defined(LWS_WITH_SYS_METRICS)
 		/*
@@ -162,13 +164,41 @@ secstream_ws(struct lws *wsi, enum lws_callback_reasons reason, void *user,
 		}
 
 		buflen = sizeof(buf) - LWS_PRE;
+
+		/*
+		 * Let's prepare *flags with information about the channel ws message state
+		 * which the callback can simply overwrite.  But if you are tracing problems
+		 * with your own flags state blowing assert()s below, you can use this for
+		 * debugging the illegal state while still in your ss tx callback; otherwise
+		 * it can be harder to understand what you're doing wrong after we returned
+		 * from the callback and blow chunks here.
+		 *
+		 * b1 of flags is set if we know the last fin state.  If b1 is set, b0 is
+		 * the last FIN state.  You can use this info to see if your flags will
+		 * cause us to assert when you return.
+		 */
+
+		f = (!!wsi->ws->last_valid << 1) | (!!wsi->ws->last_fin);
 		r = h->info.tx(ss_to_userobj(h),  h->txord++, buf + LWS_PRE,
 				  &buflen, &f);
 		if (r == LWSSSSRET_TX_DONT_SEND)
 			return 0;
 		if (r != LWSSSSRET_OK)
 			return _lws_ss_handle_state_ret_CAN_DESTROY_HANDLE(r, wsi, &h);
 
+		if ((f & LWSSS_FLAG_SOM) && wsi->ws->last_valid && !wsi->ws->last_fin) {
+			lwsl_ss_err(h, "%s TX: Illegal LWSSS_FLAG_SOM after previous frame without LWSSS_FLAG_EOM", h->policy ? h->policy->streamtype : "unknown");
+			assert(0);
+		}
+		if (!(f & LWSSS_FLAG_SOM) && wsi->ws->last_valid && wsi->ws->last_fin) {
+			lwsl_ss_err(h, "%s TX: Missing LWSSS_FLAG_SOM after previous frame with LWSSS_FLAG_EOM", h->policy ? h->policy->streamtype : "unknown");
+			assert(0);
+		}
+		if (!(f & LWSSS_FLAG_SOM) && !wsi->ws->last_valid) {
+			lwsl_ss_err(h, "%s TX: Missing LWSSS_FLAG_SOM on first frame", h->policy ? h->policy->streamtype : "unknown");
+			assert(0);
+		}
+
 		f1 = lws_write_ws_flags(h->policy->u.http.u.ws.binary ?
 					   LWS_WRITE_BINARY : LWS_WRITE_TEXT,
 					!!(f & LWSSS_FLAG_SOM),