Added pre-login event for catching logins right after name verification has completed. This happens in a different thread from the server (and thus can also block).

src/main/java/net/minecraft/server/NetLoginHandler.java

@@ -21,6 +21,12 @@ public class NetLoginHandler extends NetHandler {
         this.b = new NetworkManager(socket, s, this);
         this.b.d = 0;
     }
+    
+    // CraftBukkit start
+    public Socket getSocket() {
+        return b.f;
+    }
+    // CraftBukkit end
 
     public void a() {
         if (this.h != null) {
@@ -67,7 +73,7 @@ public class NetLoginHandler extends NetHandler {
             if (!this.e.l) {
                 this.b(packet1login);
             } else {
-                (new ThreadLoginVerifier(this, packet1login)).start();
+                (new ThreadLoginVerifier(this, packet1login, e.server)).start();
             }
         }
     }

src/main/java/net/minecraft/server/NetworkManager.java

@@ -18,7 +18,7 @@ public class NetworkManager {
     public static int b;
     public static int c;
     private Object e = new Object();
-    private Socket f;
+    public Socket f; // CraftBukkit private->public
     private final SocketAddress g;
     private DataInputStream h;
     private DataOutputStream i;

src/main/java/net/minecraft/server/ThreadLoginVerifier.java

@@ -0,0 +1,51 @@
+package net.minecraft.server;
+
+import java.io.BufferedReader;
+import java.io.InputStreamReader;
+import java.net.URL;
+import java.net.URLEncoder;
+import org.bukkit.craftbukkit.CraftServer;
+import org.bukkit.event.player.PlayerPreLoginEvent;
+
+class ThreadLoginVerifier extends Thread {
+
+    final Packet1Login a;
+
+    final NetLoginHandler b;
+    
+    // CraftBukkit start
+    CraftServer server;
+
+    ThreadLoginVerifier(NetLoginHandler netloginhandler, Packet1Login packet1login, CraftServer server) {
+        this.server = server;
+        // CraftBukkit end
+        this.b = netloginhandler;
+        this.a = packet1login;
+    }
+
+    public void run() {
+        try {
+            String s = NetLoginHandler.a(this.b);
+            URL url = new URL("http://www.minecraft.net/game/checkserver.jsp?user=" + URLEncoder.encode(this.a.b, "UTF-8") + "&serverId=" + URLEncoder.encode(s, "UTF-8"));
+            BufferedReader bufferedreader = new BufferedReader(new InputStreamReader(url.openStream()));
+            String s1 = bufferedreader.readLine();
+
+            bufferedreader.close();
+            if (s1.equals("YES")) {
+                PlayerPreLoginEvent event = new PlayerPreLoginEvent(this.a.b, b.getSocket().getInetAddress());
+                server.getPluginManager().callEvent(event);
+                
+                if (event.getResult() != PlayerPreLoginEvent.Result.ALLOWED) {
+                    this.b.a(event.getKickMessage());
+                    return;
+                }
+                
+                NetLoginHandler.a(this.b, this.a);
+            } else {
+                this.b.a("Failed to verify username!");
+            }
+        } catch (Exception exception) {
+            exception.printStackTrace();
+        }
+    }
+}