Include implementation in the user-agent.

proxy/src/main/java/com/velocitypowered/proxy/network/http/NettyHttpClient.java

@@ -25,8 +25,10 @@ import javax.net.ssl.SSLEngine;
 public class NettyHttpClient {
 
   private final ChannelPoolMap<InetSocketAddress, SimpleChannelPool> poolMap;
+  private final String userAgent;
 
   public NettyHttpClient(VelocityServer server) {
+    this.userAgent = server.getVersion().getName() + "/" + server.getVersion().getVersion();
     Bootstrap bootstrap = server.initializeGenericBootstrap();
     this.poolMap = new AbstractChannelPoolMap<InetSocketAddress, SimpleChannelPool>() {
       @Override
@@ -80,7 +82,7 @@ public class NettyHttpClient {
             DefaultFullHttpRequest request = new DefaultFullHttpRequest(HttpVersion.HTTP_1_1,
                 HttpMethod.GET, url.getPath() + "?" + url.getQuery());
             request.headers().add(HttpHeaderNames.HOST, url.getHost());
-            request.headers().add(HttpHeaderNames.USER_AGENT, "Velocity");
+            request.headers().add(HttpHeaderNames.USER_AGENT, userAgent);
             channel.writeAndFlush(request);
 
             // Make sure to release this connection

proxy/src/main/java/com/velocitypowered/proxy/network/http/SimpleHttpResponse.java

@@ -20,9 +20,9 @@ public class SimpleHttpResponse {
 
   @Override
   public String toString() {
-    return "SimpleHttpResponse{" +
-        "code=" + code +
-        ", body='" + body + '\'' +
-        '}';
+    return "SimpleHttpResponse{"
+        + "code=" + code
+        + ", body='" + body + '\''
+        + '}';
   }
 }

proxy/src/main/java/com/velocitypowered/proxy/plugin/VelocityEventManager.java

@@ -68,8 +68,7 @@ public class VelocityEventManager implements EventManager {
     ensurePlugin(plugin);
     Preconditions.checkNotNull(listener, "listener");
     if (plugin == listener && registeredListenersByPlugin.containsEntry(plugin, plugin)) {
-      throw new IllegalArgumentException(
-          "Trying to register the plugin main instance. Velocity already takes care of this for you.");
+      throw new IllegalArgumentException("The plugin main instance is automatically registered.");
     }
     registeredListenersByPlugin.put(plugin, listener);
     methodAdapter.register(listener);