Added optional "senderPeerAddress" string to HELLO messages, to allow external IP changes to be detected without using a centralized service.

src/main/java/org/qortal/network/Handshake.java

@@ -48,6 +48,9 @@ public enum Handshake {
 				return null;
 			}
 
+			// Make a note of the senderPeerAddress, as this should be our public IP
+			Network.getInstance().ourPeerAddressUpdated(helloMessage.getSenderPeerAddress());
+
 			String versionString = helloMessage.getVersionString();
 
 			Matcher matcher = peer.VERSION_PATTERN.matcher(versionString);
@@ -87,8 +90,9 @@ public enum Handshake {
 		public void action(Peer peer) {
 			String versionString = Controller.getInstance().getVersionString();
 			long timestamp = NTP.getTime();
+			String senderPeerAddress = peer.getPeerData().getAddress().toString();
 
-			Message helloMessage = new HelloMessage(timestamp, versionString);
+			Message helloMessage = new HelloMessage(timestamp, versionString, senderPeerAddress);
 			if (!peer.sendMessage(helloMessage))
 				peer.disconnect("failed to send HELLO");
 		}

src/main/java/org/qortal/network/Network.java

@@ -7,7 +7,6 @@ import org.bouncycastle.crypto.params.Ed25519PublicKeyParameters;
 import org.qortal.block.BlockChain;
 import org.qortal.controller.Controller;
 import org.qortal.controller.arbitrary.ArbitraryDataFileManager;
-import org.qortal.controller.arbitrary.ArbitraryDataManager;
 import org.qortal.crypto.Crypto;
 import org.qortal.data.block.BlockData;
 import org.qortal.data.network.PeerData;
@@ -117,6 +116,9 @@ public class Network {
 
     private final Lock mergePeersLock = new ReentrantLock();
 
+    private List<String> ourExternalIpAddressHistory = new ArrayList<>();
+    private String ourExternalIpAddress = null;
+
     // Constructors
 
     private Network() {
@@ -1102,6 +1104,65 @@ public class Network {
         return new GetUnconfirmedTransactionsMessage();
     }
 
+
+    // External IP / peerAddress tracking
+
+    public void ourPeerAddressUpdated(String peerAddress) {
+        if (peerAddress == null) {
+            return;
+        }
+
+        String[] parts = peerAddress.split(":");
+        if (parts.length != 2) {
+            return;
+        }
+        String host = parts[0];
+        try {
+            InetAddress addr = InetAddress.getByName(host);
+            if (addr.isAnyLocalAddress() || addr.isSiteLocalAddress()) {
+                // Ignore local addresses
+                return;
+            }
+        } catch (UnknownHostException e) {
+            return;
+        }
+
+        this.ourExternalIpAddressHistory.add(host);
+
+        // Limit to 10 entries
+        while (this.ourExternalIpAddressHistory.size() > 10) {
+            this.ourExternalIpAddressHistory.remove(0);
+        }
+
+        // If we've had 3 consecutive matching addresses, and they're different from
+        // our stored IP address value, treat it as updated.
+
+        int size = this.ourExternalIpAddressHistory.size();
+        if (size < 3) {
+            // Need at least 3 readings
+            return;
+        }
+
+        String ip1 = this.ourExternalIpAddressHistory.get(size - 1);
+        String ip2 = this.ourExternalIpAddressHistory.get(size - 2);
+        String ip3 = this.ourExternalIpAddressHistory.get(size - 3);
+
+        if (!Objects.equals(ip1, this.ourExternalIpAddress)) {
+            // Latest reading doesn't match our known value
+            if (Objects.equals(ip1, ip2) && Objects.equals(ip1, ip3)) {
+                // Last 3 readings were the same - i.e. more than one peer agreed on the new IP address
+                this.ourExternalIpAddress = ip1;
+                this.onExternalIpUpdate(ip1);
+            }
+        }
+    }
+
+    public void onExternalIpUpdate(String ipAddress) {
+        LOGGER.info("External IP address updated to {}", ipAddress);
+
+    }
+
+
     // Peer-management calls
 
     public void noteToSelf(Peer peer) {

src/main/java/org/qortal/network/message/HelloMessage.java

@@ -13,16 +13,18 @@ public class HelloMessage extends Message {
 
 	private final long timestamp;
 	private final String versionString;
+	private final String senderPeerAddress;
 
-	private HelloMessage(int id, long timestamp, String versionString) {
+	private HelloMessage(int id, long timestamp, String versionString, String senderPeerAddress) {
 		super(id, MessageType.HELLO);
 
 		this.timestamp = timestamp;
 		this.versionString = versionString;
+		this.senderPeerAddress = senderPeerAddress;
 	}
 
-	public HelloMessage(long timestamp, String versionString) {
-		this(-1, timestamp, versionString);
+	public HelloMessage(long timestamp, String versionString, String senderPeerAddress) {
+		this(-1, timestamp, versionString, senderPeerAddress);
 	}
 
 	public long getTimestamp() {
@@ -33,12 +35,22 @@ public class HelloMessage extends Message {
 		return this.versionString;
 	}
 
+	public String getSenderPeerAddress() {
+		return this.senderPeerAddress;
+	}
+
 	public static Message fromByteBuffer(int id, ByteBuffer byteBuffer) throws TransformationException {
 		long timestamp = byteBuffer.getLong();
 
 		String versionString = Serialization.deserializeSizedString(byteBuffer, 255);
 
-		return new HelloMessage(id, timestamp, versionString);
+		// Sender peer address added in v3.0, so is an optional field. Older versions won't send it.
+		String senderPeerAddress = null;
+		if (byteBuffer.hasRemaining()) {
+			senderPeerAddress = Serialization.deserializeSizedString(byteBuffer, 255);
+		}
+
+		return new HelloMessage(id, timestamp, versionString, senderPeerAddress);
 	}
 
 	@Override
@@ -49,6 +61,8 @@ public class HelloMessage extends Message {
 
 		Serialization.serializeSizedString(bytes, this.versionString);
 
+		Serialization.serializeSizedString(bytes, this.senderPeerAddress);
+
 		return bytes.toByteArray();
 	}