If file://con input is using O_NONBLOCK, that is fine, but use FIONREAD to make sure all the data requested is there to read first to prevent short reads that cause zero padding in the SRT stream

Author: joncampbell123

apps/transmitmedia.cpp

@@ -710,8 +710,10 @@ class ConsoleSource: public Source
     ConsoleSource()
 #ifdef _WIN32
     : may_block(true)
-#else
+#elif defined(FIONREAD)
     : may_block(fcntl(fileno(stdin), F_SETFL, fcntl(fileno(stdin), F_GETFL) | O_NONBLOCK) < 0)
+#else
+    : may_block(true)
 #endif
     {
 #ifdef _WIN32
@@ -723,6 +725,21 @@ class ConsoleSource: public Source
 
     int Read(size_t chunk, MediaPacket& pkt, ostream & ignored SRT_ATR_UNUSED = cout) override
     {
+#if defined(FIONREAD)
+        // The trouble with O_NONBLOCK is that read() may return less than the expected data if not enough available
+        // which then causes a full size SRT packet padded with zeros. Use FIONREAD, if possible, to make sure that
+	// read() returns either chunk bytes or nothing at all.
+        if (!may_block) {
+            int br = 0;
+            if (ioctl(GetSysSocket(), FIONREAD, &br) >= 0) {
+                if (br < 0 || size_t(br) < chunk) {
+                    pkt.payload.clear();
+                    return 0;
+                }
+            }
+        }
+#endif
+
         if (pkt.payload.size() < chunk)
             pkt.payload.resize(chunk);