auto-reconnect mechinism

Author: ningning-chen

src/main/java/com/cisco/trex/stateless/TRexTransport.java

@@ -142,6 +142,21 @@ public synchronized String sendJson(String json) {
     }
     byte[] msg = zmqSocket.recv();
 
+    if (msg == null) {
+      zmqSocket.connect(this.connectionString);
+      try {
+        zmqSocket.send(compressed);
+      } catch (ZMQException e) {
+        throw new IllegalStateException(
+            "Did not get any response from server "
+                + getHost()
+                + " within timeout "
+                + zmqSocket.getReceiveTimeOut(),
+            e);
+      }
+      msg = zmqSocket.recv();
+    }
+
     String response = this.dataCompressor.decompressBytesToString(msg);
     LOGGER.debug("JSON Resp: {}", response);
     return response;