explcitly define the max I2NP message ID value and validate against it

router/java/src/net/i2p/data/i2np/DatabaseStoreMessage.java

@@ -98,7 +98,18 @@ public class DatabaseStoreMessage extends I2NPMessageImpl {
      * @return positive reply token ID, or 0 if no reply is necessary.
      */
     public long getReplyToken() { return _replyToken; }
-    public void setReplyToken(long token) { _replyToken = token; }
+    /**
+     * Update the reply token.
+     *
+     * @throws IllegalArgumentException if the token is out of range (min=0, max=I2NPMessage.MAX_ID_VALUE)
+     */
+    public void setReplyToken(long token) throws IllegalArgumentException { 
+        if (token > I2NPMessage.MAX_ID_VALUE)
+            throw new IllegalArgumentException("Token too large: " + token + " (max=" + I2NPMessage.MAX_ID_VALUE + ")");
+        else if (token < 0) 
+            throw new IllegalArgumentException("Token too small: " + token);
+        _replyToken = token; 
+    }
     
     public TunnelId getReplyTunnel() { return _replyTunnel; } 
     public void setReplyTunnel(TunnelId id) { _replyTunnel = id; }

router/java/src/net/i2p/data/i2np/I2NPMessage.java

@@ -20,6 +20,8 @@ import net.i2p.data.DataStructure;
  * @author jrandom
  */
 public interface I2NPMessage extends DataStructure {
+    final long MAX_ID_VALUE = (1l<<32l)-1l;
+    
     /**
      * Read the body into the data structures, after the initial type byte, using
      * the current class's format as defined by the I2NP specification

router/java/src/net/i2p/data/i2np/I2NPMessageImpl.java

@@ -36,7 +36,7 @@ public abstract class I2NPMessageImpl extends DataStructureImpl implements I2NPM
         _context = context;
         _log = context.logManager().getLog(I2NPMessageImpl.class);
         _expiration = new Date(_context.clock().now() + DEFAULT_EXPIRATION_MS);
-        _uniqueId = _context.random().nextInt(Integer.MAX_VALUE);
+        _uniqueId = _context.random().nextLong(MAX_ID_VALUE);
     }
     
     /**