issue #4: prevent connections to self, select random nodes to connect to

domain/src/main/java/ch/dissem/bitmessage/InternalContext.java

@@ -52,6 +52,7 @@ public class InternalContext {
     private final int port;
     private long networkNonceTrialsPerByte = 1000;
     private long networkExtraBytes = 1000;
+    private long clientNonce;
 
     public InternalContext(BitmessageContext.Builder builder) {
         this.inventory = builder.inventory;
@@ -60,6 +61,7 @@ public class InternalContext {
         this.addressRepository = builder.addressRepo;
         this.messageRepository = builder.messageRepo;
         this.proofOfWorkEngine = builder.proofOfWorkEngine;
+        this.clientNonce = Security.randomNonce();
 
         port = builder.port;
         streams = builder.streams;
@@ -212,6 +214,14 @@ public class InternalContext {
         }
     }
 
+    public long getClientNonce() {
+        return clientNonce;
+    }
+
+    public void setClientNonce(long clientNonce) {
+        this.clientNonce = clientNonce;
+    }
+
     public interface ContextHolder {
         void setContext(InternalContext context);
     }

domain/src/main/java/ch/dissem/bitmessage/utils/Security.java

@@ -230,4 +230,8 @@ public class Security {
             throw new RuntimeException(e);
         }
     }
+
+    public static long randomNonce() {
+        return RANDOM.nextLong();
+    }
 }

networking/src/main/java/ch/dissem/bitmessage/networking/Connection.java

@@ -102,7 +102,10 @@ public class Connection implements Runnable {
                         switch (msg.getPayload().getCommand()) {
                             case VERSION:
                                 Version payload = (Version) msg.getPayload();
-                                if (payload.getVersion() >= BitmessageContext.CURRENT_VERSION) {
+                                if (payload.getNonce() == ctx.getClientNonce()) {
+                                    LOG.info("Tried to connect to self, disconnecting.");
+                                    disconnect();
+                                } else if (payload.getVersion() >= BitmessageContext.CURRENT_VERSION) {
                                     this.version = payload.getVersion();
                                     this.streams = payload.getStreams();
                                     send(new VerAck());
@@ -120,8 +123,8 @@ public class Connection implements Runnable {
                                 }
                                 break;
                             default:
-                                throw new RuntimeException("Command 'version' or 'verack' expected, but was "
-                                        + msg.getPayload().getCommand());
+                                throw new RuntimeException("Command 'version' or 'verack' expected, but was '"
+                                        + msg.getPayload().getCommand() + "'");
                         }
                 }
                 if (socket.isClosed()) state = DISCONNECTED;

repositories/src/main/java/ch/dissem/bitmessage/repository/JdbcNodeRegistry.java

@@ -37,7 +37,7 @@ public class JdbcNodeRegistry extends JdbcHelper implements NodeRegistry {
         List<NetworkAddress> result = new LinkedList<>();
         try (Connection connection = config.getConnection()) {
             Statement stmt = connection.createStatement();
-            ResultSet rs = stmt.executeQuery("SELECT * FROM Node WHERE stream IN (" + join(streams) + ") LIMIT " + limit);
+            ResultSet rs = stmt.executeQuery("SELECT * FROM Node WHERE stream IN (" + join(streams) + ") ORDER BY RANDOM() LIMIT " + limit);
             while (rs.next()) {
                 result.add(new NetworkAddress.Builder()
                         .ipv6(rs.getBytes("ip"))