Add Query event

api/src/main/java/com/velocitypowered/api/event/query/ProxyQueryEvent.java

@@ -0,0 +1,83 @@
+package com.velocitypowered.api.event.query;
+
+import com.google.common.base.Preconditions;
+import com.velocitypowered.api.proxy.server.QueryResponse;
+import org.checkerframework.checker.nullness.qual.NonNull;
+
+import java.net.InetAddress;
+
+/**
+ * This event is fired if proxy is getting queried over GS4 Query protocol
+ */
+public final class ProxyQueryEvent {
+    private final QueryType queryType;
+    private final InetAddress querierAddress;
+    private QueryResponse response;
+
+    public ProxyQueryEvent(QueryType queryType, InetAddress querierAddress, QueryResponse response) {
+        this.queryType = Preconditions.checkNotNull(queryType, "queryType");
+        this.querierAddress = Preconditions.checkNotNull(querierAddress, "querierAddress");
+        this.response = Preconditions.checkNotNull(response, "response");
+    }
+
+    /**
+     * Get query type
+     * @return query type
+     */
+    @NonNull
+    public QueryType getQueryType() {
+        return queryType;
+    }
+
+    /**
+     * Get querier address
+     * @return querier address
+     */
+    @NonNull
+    public InetAddress getQuerierAddress() {
+        return querierAddress;
+    }
+
+    /**
+     * Get query response
+     * @return query response
+     */
+    @NonNull
+    public QueryResponse getResponse() {
+        return response;
+    }
+
+    /**
+     * Set query response
+     * @param response query response
+     */
+    public void setResponse(@NonNull QueryResponse response) {
+        this.response = Preconditions.checkNotNull(response, "response");
+    }
+
+    @Override
+    public String toString() {
+        return "ProxyQueryEvent{" +
+                "queryType=" + queryType +
+                ", querierAddress=" + querierAddress +
+                ", response=" + response +
+                '}';
+    }
+
+    /**
+     * The type of query
+     */
+    public enum QueryType {
+        /**
+         * Basic query asks only a subset of information, such as hostname, game type (hardcoded to <pre>MINECRAFT</pre>), map,
+         * current players, max players, proxy port and proxy hostname
+         */
+        BASIC,
+
+        /**
+         * Full query asks pretty much everything present on this event (only hardcoded values cannot be modified here).
+         */
+        FULL
+        ;
+    }
+}

api/src/main/java/com/velocitypowered/api/event/query/package-info.java

@@ -0,0 +1,4 @@
+/**
+ * Provides events for handling GS4 queries.
+ */
+package com.velocitypowered.api.event.query;

api/src/main/java/com/velocitypowered/api/proxy/config/ProxyConfig.java

@@ -29,6 +29,13 @@ public interface ProxyConfig {
      */
     String getQueryMap();
 
+    /**
+     * Whether GameSpy 4 queries should show plugins installed on
+     * Velocity by default
+     * @return show plugins in query
+     */
+    boolean shouldQueryShowPlugins();
+
     /**
      * Get the MOTD component shown in the tab list
      * @return the motd component

api/src/main/java/com/velocitypowered/api/proxy/server/QueryResponse.java

@@ -0,0 +1,318 @@
+package com.velocitypowered.api.proxy.server;
+
+import com.google.common.base.Preconditions;
+import com.google.common.collect.ImmutableList;
+import com.velocitypowered.api.proxy.config.ProxyConfig;
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.List;
+
+/**
+ * GS4 query response. This class is immutable.
+ */
+public final class QueryResponse {
+    private final String hostname;
+    private final String gameVersion;
+    private final String map;
+    private final int currentPlayers;
+    private final int maxPlayers;
+    private final String proxyHost;
+    private final int proxyPort;
+    private final Collection<String> players;
+    private final String proxyVersion;
+    private final Collection<PluginInformation> plugins;
+
+    private QueryResponse(String hostname, String gameVersion, String map, int currentPlayers, int maxPlayers, String proxyHost, int proxyPort, Collection<String> players, String proxyVersion, Collection<PluginInformation> plugins) {
+        this.hostname = hostname;
+        this.gameVersion = gameVersion;
+        this.map = map;
+        this.currentPlayers = currentPlayers;
+        this.maxPlayers = maxPlayers;
+        this.proxyHost = proxyHost;
+        this.proxyPort = proxyPort;
+        this.players = players;
+        this.proxyVersion = proxyVersion;
+        this.plugins = plugins;
+    }
+
+    /**
+     * Get hostname which will be used to reply to the query. By default it is {@link ProxyConfig#getMotdComponent()} in plain text without colour codes.
+     * @return hostname
+     */
+    @NonNull
+    public String getHostname() {
+        return hostname;
+    }
+
+    /**
+     * Get game version which will be used to reply to the query. By default supported Minecraft versions range is sent.
+     * @return game version
+     */
+    @NonNull
+    public String getGameVersion() {
+        return gameVersion;
+    }
+
+    /**
+     * Get map name which will be used to reply to the query. By default {@link ProxyConfig#getQueryMap()} is sent.
+     * @return map name
+     */
+    @NonNull
+    public String getMap() {
+        return map;
+    }
+
+    /**
+     * Get current online player count which will be used to reply to the query.
+     * @return online player count
+     */
+    public int getCurrentPlayers() {
+        return currentPlayers;
+    }
+
+    /**
+     * Get max player count which will be used to reply to the query.
+     * @return max player count
+     */
+    public int getMaxPlayers() {
+        return maxPlayers;
+    }
+
+    /**
+     * Get proxy (public facing) hostname
+     * @return proxy hostname
+     */
+    @NonNull
+    public String getProxyHost() {
+        return proxyHost;
+    }
+
+    /**
+     * Get proxy (public facing) port
+     * @return proxy port
+     */
+    public int getProxyPort() {
+        return proxyPort;
+    }
+
+    /**
+     * Get collection of players which will be used to reply to the query.
+     * @return collection of players
+     */
+    @NonNull
+    public Collection<String> getPlayers() {
+        return players;
+    }
+
+    /**
+     * Get server software (name and version) which will be used to reply to the query.
+     * @return server software
+     */
+    @NonNull
+    public String getProxyVersion() {
+        return proxyVersion;
+    }
+
+    /**
+     * Get list of plugins which will be used to reply to the query.
+     * @return collection of plugins
+     */
+    @NonNull
+    public Collection<PluginInformation> getPlugins() {
+        return plugins;
+    }
+
+
+    /**
+     * Creates a new {@link Builder} instance from data represented by this response
+     * @return {@link QueryResponse} builder
+     */
+    @NonNull
+    public Builder toBuilder() {
+        return QueryResponse.builder()
+                .hostname(getHostname())
+                .gameVersion(getGameVersion())
+                .map(getMap())
+                .currentPlayers(getCurrentPlayers())
+                .maxPlayers(getMaxPlayers())
+                .proxyHost(getProxyHost())
+                .proxyPort(getProxyPort())
+                .players(getPlayers())
+                .proxyVersion(getProxyVersion())
+                .plugins(getPlugins());
+    }
+
+    /**
+     * Creates a new {@link Builder} instance
+     * @return {@link QueryResponse} builder
+     */
+    @NonNull
+    public static Builder builder() {
+        return new Builder();
+    }
+
+    /**
+     * A builder for {@link QueryResponse} objects.
+     */
+    public static final class Builder {
+        private String hostname;
+        private String gameVersion;
+        private String map;
+        private int currentPlayers;
+        private int maxPlayers;
+        private String proxyHost;
+        private int proxyPort;
+        private Collection<String> players = new ArrayList<>();
+        private String proxyVersion;
+        private List<PluginInformation> plugins = new ArrayList<>();
+
+        private Builder() {}
+
+        @NonNull
+        public Builder hostname(@NonNull String hostname) {
+            this.hostname = Preconditions.checkNotNull(hostname, "hostname");
+            return this;
+        }
+
+        @NonNull
+        public Builder gameVersion(@NonNull String gameVersion) {
+            this.gameVersion = Preconditions.checkNotNull(gameVersion, "gameVersion");
+            return this;
+        }
+
+        @NonNull
+        public Builder map(@NonNull String map) {
+            this.map = Preconditions.checkNotNull(map, "map");
+            return this;
+        }
+
+        @NonNull
+        public Builder currentPlayers(int currentPlayers) {
+            Preconditions.checkArgument(currentPlayers >= 0, "currentPlayers cannot be negative");
+            this.currentPlayers = currentPlayers;
+            return this;
+        }
+
+        @NonNull
+        public Builder maxPlayers(int maxPlayers) {
+            Preconditions.checkArgument(maxPlayers >= 0, "maxPlayers cannot be negative");
+            this.maxPlayers = maxPlayers;
+            return this;
+        }
+
+        @NonNull
+        public Builder proxyHost(@NonNull String proxyHost) {
+            this.proxyHost = Preconditions.checkNotNull(proxyHost, "proxyHost");
+            return this;
+        }
+
+        @NonNull
+        public Builder proxyPort(int proxyPort) {
+            Preconditions.checkArgument(proxyPort >= 1 && proxyPort <= 65535, "proxyPort must be between 1-65535");
+            this.proxyPort = proxyPort;
+            return this;
+        }
+
+        @NonNull
+        public Builder players(@NonNull Collection<String> players) {
+            this.players.addAll(Preconditions.checkNotNull(players, "players"));
+            return this;
+        }
+
+        @NonNull
+        public Builder players(@NonNull String... players) {
+            this.players.addAll(Arrays.asList(Preconditions.checkNotNull(players, "players")));
+            return this;
+        }
+
+        @NonNull
+        public Builder clearPlayers() {
+            this.players.clear();
+            return this;
+        }
+
+        @NonNull
+        public Builder proxyVersion(@NonNull String proxyVersion) {
+            this.proxyVersion = Preconditions.checkNotNull(proxyVersion, "proxyVersion");
+            return this;
+        }
+
+        @NonNull
+        public Builder plugins(@NonNull Collection<PluginInformation> plugins) {
+            this.plugins.addAll(Preconditions.checkNotNull(plugins, "plugins"));
+            return this;
+        }
+
+        @NonNull
+        public Builder plugins(@NonNull PluginInformation... plugins) {
+            this.plugins.addAll(Arrays.asList(Preconditions.checkNotNull(plugins, "plugins")));
+            return this;
+        }
+
+        @NonNull
+        public Builder clearPlugins() {
+            this.plugins.clear();
+            return this;
+        }
+
+        /**
+         * Builds new {@link QueryResponse} with supplied data
+         * @return response
+         */
+        @NonNull
+        public QueryResponse build() {
+            return new QueryResponse(
+                    hostname,
+                    gameVersion,
+                    map,
+                    currentPlayers,
+                    maxPlayers,
+                    proxyHost,
+                    proxyPort,
+                    ImmutableList.copyOf(players),
+                    proxyVersion,
+                    ImmutableList.copyOf(plugins)
+            );
+        }
+    }
+
+    /**
+     * Plugin information
+     */
+    public static class PluginInformation {
+        private String name;
+        private String version;
+
+        public PluginInformation(@NonNull String name, @Nullable String version) {
+            this.name = name;
+            this.version = version;
+        }
+
+        @NonNull
+        public String getName() {
+            return name;
+        }
+
+        public void setName(@NonNull String name) {
+            this.name = name;
+        }
+
+        public void setVersion(@Nullable String version) {
+            this.version = version;
+        }
+
+        @Nullable
+        public String getVersion() {
+            return version;
+        }
+
+        @NonNull
+        public static PluginInformation of(@NonNull String name, @Nullable String version) {
+            return new PluginInformation(name, version);
+        }
+    }
+}

proxy/src/main/java/com/velocitypowered/proxy/config/VelocityConfiguration.java

@@ -213,6 +213,11 @@ public class VelocityConfiguration extends AnnotatedConfig implements ProxyConfi
         return query.getQueryMap();
     }
 
+    @Override
+    public boolean shouldQueryShowPlugins() {
+        return query.shouldQueryShowPlugins();
+    }
+
     public String getMotd() {
         return motd;
     }
@@ -504,6 +509,10 @@ public class VelocityConfiguration extends AnnotatedConfig implements ProxyConfi
         @ConfigKey("map")
         private String queryMap = "Velocity";
 
+        @Comment("Whether plugins should be shown in query response by default or not")
+        @ConfigKey("show-plugins")
+        private boolean showPlugins = false;
+
         private Query() {
         }
 
@@ -533,13 +542,18 @@ public class VelocityConfiguration extends AnnotatedConfig implements ProxyConfi
             return queryMap;
         }
 
+        public boolean shouldQueryShowPlugins() {
+            return showPlugins;
+        }
+
         @Override
         public String toString() {
-            return "Query{"
-                    + "queryEnabled=" + queryEnabled
-                    + ", queryPort=" + queryPort
-                    + ", queryMap=" + queryMap
-                    + '}';
+            return "Query{" +
+                    "queryEnabled=" + queryEnabled +
+                    ", queryPort=" + queryPort +
+                    ", queryMap='" + queryMap + '\'' +
+                    ", showPlugins=" + showPlugins +
+                    '}';
         }
     }
 }

proxy/src/main/java/com/velocitypowered/proxy/protocol/netty/GS4QueryHandler.java

@@ -3,7 +3,10 @@ package com.velocitypowered.proxy.protocol.netty;
 import com.google.common.cache.Cache;
 import com.google.common.cache.CacheBuilder;
 import com.google.common.collect.ImmutableSet;
+import com.velocitypowered.api.event.query.ProxyQueryEvent;
+import com.velocitypowered.api.plugin.PluginContainer;
 import com.velocitypowered.api.proxy.Player;
+import com.velocitypowered.api.proxy.server.QueryResponse;
 import com.velocitypowered.proxy.VelocityServer;
 import com.velocitypowered.proxy.protocol.ProtocolConstants;
 import io.netty.buffer.ByteBuf;
@@ -17,9 +20,16 @@ import org.apache.logging.log4j.Logger;
 import java.net.InetAddress;
 import java.nio.charset.StandardCharsets;
 import java.util.Collection;
+import java.util.Collections;
+import java.util.Iterator;
+import java.util.List;
 import java.util.Set;
 import java.util.concurrent.ThreadLocalRandom;
 import java.util.concurrent.TimeUnit;
+import java.util.stream.Collectors;
+
+import static com.velocitypowered.api.event.query.ProxyQueryEvent.QueryType.BASIC;
+import static com.velocitypowered.api.event.query.ProxyQueryEvent.QueryType.FULL;
 
 public class GS4QueryHandler extends SimpleChannelInboundHandler<DatagramPacket> {
     private static final Logger logger = LogManager.getLogger(GS4QueryHandler.class);
@@ -46,6 +56,8 @@ public class GS4QueryHandler extends SimpleChannelInboundHandler<DatagramPacket>
             .expireAfterWrite(30, TimeUnit.SECONDS)
             .build();
 
+    private volatile List<QueryResponse.PluginInformation> pluginInformationList = null;
+
     private final VelocityServer server;
 
     public GS4QueryHandler(VelocityServer server) {
@@ -81,6 +93,7 @@ public class GS4QueryHandler extends SimpleChannelInboundHandler<DatagramPacket>
                     queryResponse.writeByte(QUERY_TYPE_HANDSHAKE);
                     queryResponse.writeInt(sessionId);
                     writeString(queryResponse, Integer.toString(challengeToken));
+                    ctx.writeAndFlush(responsePacket);
                     break;
                 }
 
@@ -97,28 +110,51 @@ public class GS4QueryHandler extends SimpleChannelInboundHandler<DatagramPacket>
                         throw new IllegalStateException("Invalid query packet");
                     }
 
-                    // Packet header
-                    queryResponse.writeByte(QUERY_TYPE_STAT);
-                    queryResponse.writeInt(sessionId);
+                    // Build query response
+                    QueryResponse response = QueryResponse.builder()
+                            .hostname(ComponentSerializers.PLAIN.serialize(server.getConfiguration().getMotdComponent()))
+                            .gameVersion(ProtocolConstants.SUPPORTED_GENERIC_VERSION_STRING)
+                            .map(server.getConfiguration().getQueryMap())
+                            .currentPlayers(server.getPlayerCount())
+                            .maxPlayers(server.getConfiguration().getShowMaxPlayers())
+                            .proxyPort(server.getConfiguration().getBind().getPort())
+                            .proxyHost(server.getConfiguration().getBind().getHostString())
+                            .players(server.getAllPlayers().stream().map(Player::getUsername).collect(Collectors.toList()))
+                            .proxyVersion("Velocity")
+                            .plugins(server.getConfiguration().shouldQueryShowPlugins() ? getRealPluginInformation() : Collections.emptyList())
+                            .build();
 
-                    // Start writing the response
-                    ResponseWriter responseWriter = new ResponseWriter(queryResponse, queryMessage.readableBytes() == 0);
-                    responseWriter.write("hostname", ComponentSerializers.PLAIN.serialize(server.getConfiguration().getMotdComponent()));
-                    responseWriter.write("gametype", "SMP");
+                    boolean isBasic = queryMessage.readableBytes() == 0;
 
-                    responseWriter.write("game_id", "MINECRAFT");
-                    responseWriter.write("version", ProtocolConstants.SUPPORTED_GENERIC_VERSION_STRING);
-                    responseWriter.write("plugins", "");
+                    // Call event and write response
+                    server.getEventManager().fire(new ProxyQueryEvent(isBasic ? BASIC : FULL, senderAddress, response)).whenCompleteAsync((event, exc) -> {
+                        // Packet header
+                        queryResponse.writeByte(QUERY_TYPE_STAT);
+                        queryResponse.writeInt(sessionId);
 
-                    responseWriter.write("map", server.getConfiguration().getQueryMap());
-                    responseWriter.write("numplayers", server.getPlayerCount());
-                    responseWriter.write("maxplayers", server.getConfiguration().getShowMaxPlayers());
-                    responseWriter.write("hostport", server.getConfiguration().getBind().getPort());
-                    responseWriter.write("hostip", server.getConfiguration().getBind().getHostString());
+                        // Start writing the response
+                        ResponseWriter responseWriter = new ResponseWriter(queryResponse, isBasic);
+                        responseWriter.write("hostname", event.getResponse().getHostname());
+                        responseWriter.write("gametype", "SMP");
+
+                        responseWriter.write("game_id", "MINECRAFT");
+                        responseWriter.write("version", event.getResponse().getGameVersion());
+                        responseWriter.writePlugins(event.getResponse().getProxyVersion(), event.getResponse().getPlugins());
+
+                        responseWriter.write("map", event.getResponse().getMap());
+                        responseWriter.write("numplayers", event.getResponse().getCurrentPlayers());
+                        responseWriter.write("maxplayers", event.getResponse().getMaxPlayers());
+                        responseWriter.write("hostport", event.getResponse().getProxyPort());
+                        responseWriter.write("hostip", event.getResponse().getProxyHost());
+
+                        if (!responseWriter.isBasic) {
+                            responseWriter.writePlayers(event.getResponse().getPlayers());
+                        }
+
+                        // Send the response
+                        ctx.writeAndFlush(responsePacket);
+                    }, ctx.channel().eventLoop());
 
-                    if (!responseWriter.isBasic) {
-                        responseWriter.writePlayers(server.getAllPlayers());
-                    }
                     break;
                 }
 
@@ -126,9 +162,6 @@ public class GS4QueryHandler extends SimpleChannelInboundHandler<DatagramPacket>
                     throw new IllegalStateException("Invalid query type: " + type);
                 }
             }
-
-            // Send the response
-            ctx.writeAndFlush(responsePacket);
         } catch (Exception e) {
             logger.warn("Error while trying to handle a query packet from {}", msg.sender(), e);
             // NB: Only need to explicitly release upon exception, writing the response out will decrement the reference
@@ -142,6 +175,22 @@ public class GS4QueryHandler extends SimpleChannelInboundHandler<DatagramPacket>
         buf.writeByte(0x00);
     }
 
+    private List<QueryResponse.PluginInformation> getRealPluginInformation() {
+        // Effective Java, Third Edition; Item 83: Use lazy initialization judiciously
+        List<QueryResponse.PluginInformation> res = pluginInformationList;
+        if (res == null) {
+            synchronized (this) {
+                if (pluginInformationList == null) {
+                    pluginInformationList = res = server.getPluginManager().getPlugins().stream()
+                            .map(PluginContainer::getDescription)
+                            .map(desc -> QueryResponse.PluginInformation.of(desc.getName().orElse(desc.getId()), desc.getVersion().orElse(null)))
+                            .collect(Collectors.toList());
+                }
+            }
+        }
+        return res;
+    }
+
     private static class ResponseWriter {
         private final ByteBuf buf;
         private final boolean isBasic;
@@ -180,7 +229,7 @@ public class GS4QueryHandler extends SimpleChannelInboundHandler<DatagramPacket>
 
         // Ends packet k/v body writing and writes stat player list to
         // the packet if this writer is initialized for full stat response
-        void writePlayers(Collection<Player> players) {
+        void writePlayers(Collection<String> players) {
             if (isBasic) {
                 return;
             }
@@ -189,8 +238,29 @@ public class GS4QueryHandler extends SimpleChannelInboundHandler<DatagramPacket>
             buf.writeByte(0x00);
 
             buf.writeBytes(QUERY_RESPONSE_FULL_PADDING2);
-            players.forEach(player -> writeString(buf, player.getUsername()));
+            players.forEach(player -> writeString(buf, player));
             buf.writeByte(0x00);
         }
+
+        void writePlugins(String serverVersion, Collection<QueryResponse.PluginInformation> plugins) {
+            if (isBasic)
+                return;
+
+            StringBuilder pluginsString = new StringBuilder();
+            pluginsString.append(serverVersion).append(':').append(' ');
+            Iterator<QueryResponse.PluginInformation> iterator = plugins.iterator();
+            while (iterator.hasNext()) {
+                QueryResponse.PluginInformation info = iterator.next();
+                pluginsString.append(info.getName());
+                if (info.getVersion() != null) {
+                    pluginsString.append(' ').append(info.getVersion());
+                }
+                if (iterator.hasNext()) {
+                    pluginsString.append(';').append(' ');
+                }
+            }
+
+            writeString(buf, pluginsString.toString());
+        }
     }
 }