From a8bdae7ca42cdd210f50abacf1aea255204a10f5 Mon Sep 17 00:00:00 2001
From: Luigi Gubello <l.gubello@arduino.cc>
Date: Mon, 31 Aug 2020 02:25:05 +0200
Subject: [PATCH] Added method to set random local port

Added method to set a random local port, so that the board needs not
to use always the same embedded local port for receiving NTP packets.
---
 NTPClient.cpp | 12 +++++++++---
 NTPClient.h   |  9 +++++++--
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/NTPClient.cpp b/NTPClient.cpp
index fffe105..ddb76fb 100755
--- a/NTPClient.cpp
+++ b/NTPClient.cpp
@@ -73,7 +73,7 @@ void NTPClient::begin() {
   this->begin(NTP_DEFAULT_LOCAL_PORT);
 }
 
-void NTPClient::begin(int port) {
+void NTPClient::begin(long port) {
   this->_port = port;
 
   this->_udp->begin(this->_port);
@@ -120,7 +120,7 @@ bool NTPClient::forceUpdate() {
 bool NTPClient::update() {
   if ((millis() - this->_lastUpdate >= this->_updateInterval)     // Update after _updateInterval
     || this->_lastUpdate == 0) {                                // Update if there was no update yet.
-    if (!this->_udpSetup) this->begin();                         // setup the UDP client if needed
+    if (!this->_udpSetup || this->_port != NTP_DEFAULT_LOCAL_PORT) this->begin(this->_port); // setup the UDP client if needed
     return this->forceUpdate();
   }
   return false;   // return false if update does not occur
@@ -181,7 +181,8 @@ void NTPClient::sendNTPPacket() {
   // set all bytes in the buffer to 0
   memset(this->_packetBuffer, 0, NTP_PACKET_SIZE);
   // Initialize values needed to form NTP request
-  // (see URL above for details on the packets)
+  // (see URL above for details on the packets)  Serial.println(this->_port);
+
   this->_packetBuffer[0] = 0b11100011;   // LI, Version, Mode
   this->_packetBuffer[1] = 0;     // Stratum, or type of clock
   this->_packetBuffer[2] = 6;     // Polling Interval
@@ -202,3 +203,8 @@ void NTPClient::sendNTPPacket() {
   this->_udp->write(this->_packetBuffer, NTP_PACKET_SIZE);
   this->_udp->endPacket();
 }
+
+void NTPClient::setRandomPort() {
+  randomSeed(analogRead(0));
+  this->_port = random(1, 65534);
+}
\ No newline at end of file
diff --git a/NTPClient.h b/NTPClient.h
index 20ec43b..6498e82 100755
--- a/NTPClient.h
+++ b/NTPClient.h
@@ -15,7 +15,7 @@ class NTPClient {
 
     const char*   _poolServerName = "pool.ntp.org"; // Default time server
     IPAddress     _poolServerIP;
-    int           _port           = NTP_DEFAULT_LOCAL_PORT;
+    long           _port           = NTP_DEFAULT_LOCAL_PORT;
     long          _timeOffset     = 0;
 
     unsigned long _updateInterval = 60000;  // In ms
@@ -44,6 +44,11 @@ class NTPClient {
      */
     void setPoolServerName(const char* poolServerName);
 
+     /**
+     * Set random local port
+     */
+    void setRandomPort();
+
     /**
      * Starts the underlying UDP client with the default local port
      */
@@ -52,7 +57,7 @@ class NTPClient {
     /**
      * Starts the underlying UDP client with the specified local port
      */
-    void begin(int port);
+    void begin(long port);
 
     /**
      * This should be called in the main loop of your application. By default an update from the NTP Server is only