Derive the server's unique id from its handshake key

TS3 derives a virtual server's unique identifier from its public key the
same way as a client's: base64(SHA-1(key)). The server never tells a
guest otherwise, as serverinfo is refused and neither initserver nor
notifyserverupdated carries it. The socket now keeps the key from
initivexpand(2) and offers getServerUid().

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/main/java/com/github/manevolent/ts3j/protocol/packet/handler/client/LocalClientHandlerConnecting.java

@@ -204,6 +204,7 @@ public class LocalClientHandlerConnecting extends LocalClientHandler {
                 byte[] alpha = Base64.getDecoder().decode(command.get("alpha").getValue()); // alpha
                 byte[] beta = Base64.getDecoder().decode(command.get("beta").getValue()); // beta
                 byte[] omega = Base64.getDecoder().decode(command.get("omega").getValue()); // omega
+                getClient().setServerPublicKey(command.get("omega").getValue());
 
                 getClient().setSecureParameters(Ts3Crypt.cryptoInit(alpha, beta, omega, getClient().getIdentity()));
 
@@ -224,6 +225,7 @@ public class LocalClientHandlerConnecting extends LocalClientHandler {
 
                 byte[] beta = Base64.getDecoder().decode(command.get("beta").getValue()); // beta
                 byte[] omega = Base64.getDecoder().decode(command.get("omega").getValue()); // omega
+                getClient().setServerPublicKey(command.get("omega").getValue());
                 byte[] proof = Base64.getDecoder().decode(command.get("proof").getValue());
 
                 Pair<byte[], byte[]> keyPair = Ts3Crypt.generateKeypair();

src/main/java/com/github/manevolent/ts3j/protocol/socket/client/LocalTeamspeakClientSocket.java

@@ -32,6 +32,9 @@ import java.io.IOException;
 import java.net.*;
 import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
+import java.nio.charset.StandardCharsets;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
 import java.util.*;
 import java.util.concurrent.*;
 import java.util.function.Function;
@@ -59,6 +62,9 @@ public class LocalTeamspeakClientSocket
     /** The virtual server's properties as announced by <b>initserver</b>. */
     private volatile Map<String, String> serverProperties = Collections.emptyMap();
 
+    /** The public key the server identified itself with in the handshake, base64 as sent. */
+    private volatile String serverPublicKey;
+
     /**
      * The internal command buffer
      * <p>
@@ -325,6 +331,7 @@ public class LocalTeamspeakClientSocket
 
         serverId = null;
         serverProperties = Collections.emptyMap();
+        serverPublicKey = null;
 
         remote = null;
     }
@@ -399,6 +406,7 @@ public class LocalTeamspeakClientSocket
             // Free stuff
             serverId = null;
             serverProperties = Collections.emptyMap();
+            serverPublicKey = null;
 
 
             synchronized (commandSendLock) {
@@ -840,6 +848,25 @@ public class LocalTeamspeakClientSocket
         return serverProperties;
     }
 
+    public void setServerPublicKey(String serverPublicKey) {
+        this.serverPublicKey = serverPublicKey;
+    }
+
+    /**
+     * The virtual server's unique identifier, or null before the handshake. It is derived from
+     * the server's public key as a client's is from its own; the server tells a client no other
+     * way, as guests may not read it with <b>serverinfo</b>.
+     */
+    public Uid getServerUid() {
+        String key = serverPublicKey;
+        if (key == null) return null;
+        try {
+            return new Uid(MessageDigest.getInstance("SHA-1").digest(key.getBytes(StandardCharsets.US_ASCII)));
+        } catch (NoSuchAlgorithmException e) {
+            throw new IllegalStateException(e);
+        }
+    }
+
     /** The virtual server's name, or null if it was not announced. */
     public String getServerName() {
         return serverProperties.get("virtualserver_name");

src/test/java/com/github/manevolent/ts3j/ServerUidTest.java

@@ -0,0 +1,15 @@
+package com.github.manevolent.ts3j;
+
+import com.github.manevolent.ts3j.protocol.socket.client.LocalTeamspeakClientSocket;
+import junit.framework.TestCase;
+
+public class ServerUidTest extends TestCase {
+    /** A real server's handshake key, and the unique id the official client files its chat logs under. */
+    public void testDerivedFromTheHandshakeKey() {
+        LocalTeamspeakClientSocket client = new LocalTeamspeakClientSocket();
+        assertNull(client.getServerUid());
+
+        client.setServerPublicKey("MEwDAgcAAgEgAiEAtg1UQ4UpfiyTjrYPQcWV7Pa04/HTWr/viRhqEOg7+MQCIH/FqUKJDpBJDn/v01KOR+snSWlcoxOsfb2R8C02T3/z");
+        assertEquals("+Tyg2JtxE8vRNZp+JiUBnmBh0MY=", client.getServerUid().toBase64());
+    }
+}