Cherry-pick full Unix domain socket support from b00389029f

Closes #991. We can't properly support this without an API break, so let's just do it in 5.0.0.

api/src/main/java/com/velocitypowered/api/event/proxy/ListenerBoundEvent.java

@@ -9,22 +9,22 @@ package com.velocitypowered.api.event.proxy;
 
 import com.google.common.base.Preconditions;
 import com.velocitypowered.api.network.ListenerType;
-import java.net.InetSocketAddress;
+import java.net.SocketAddress;
 
 /**
  * This event is fired by the proxy after a listener starts accepting connections.
  */
 public final class ListenerBoundEvent {
 
-  private final InetSocketAddress address;
+  private final SocketAddress address;
   private final ListenerType listenerType;
 
-  public ListenerBoundEvent(InetSocketAddress address, ListenerType listenerType) {
+  public ListenerBoundEvent(SocketAddress address, ListenerType listenerType) {
     this.address = Preconditions.checkNotNull(address, "address");
     this.listenerType = Preconditions.checkNotNull(listenerType, "listenerType");
   }
 
-  public InetSocketAddress getAddress() {
+  public SocketAddress getAddress() {
     return address;
   }
 

api/src/main/java/com/velocitypowered/api/event/proxy/ListenerCloseEvent.java

@@ -9,22 +9,22 @@ package com.velocitypowered.api.event.proxy;
 
 import com.google.common.base.Preconditions;
 import com.velocitypowered.api.network.ListenerType;
-import java.net.InetSocketAddress;
+import java.net.SocketAddress;
 
 /**
  * This event is fired by the proxy before the proxy stops accepting connections.
  */
 public final class ListenerCloseEvent {
 
-  private final InetSocketAddress address;
+  private final SocketAddress address;
   private final ListenerType listenerType;
 
-  public ListenerCloseEvent(InetSocketAddress address, ListenerType listenerType) {
+  public ListenerCloseEvent(SocketAddress address, ListenerType listenerType) {
     this.address = Preconditions.checkNotNull(address, "address");
     this.listenerType = Preconditions.checkNotNull(listenerType, "listenerType");
   }
 
-  public InetSocketAddress getAddress() {
+  public SocketAddress getAddress() {
     return address;
   }
 

api/src/main/java/com/velocitypowered/api/proxy/InboundConnection.java

@@ -9,6 +9,7 @@ package com.velocitypowered.api.proxy;
 
 import com.velocitypowered.api.network.ProtocolVersion;
 import java.net.InetSocketAddress;
+import java.net.SocketAddress;
 import java.util.Optional;
 
 /**
@@ -17,11 +18,11 @@ import java.util.Optional;
 public interface InboundConnection {
 
   /**
-   * Returns the player's IP address.
+   * Returns the player's remote address.
    *
-   * @return the player's IP
+   * @return the player's remote address
    */
-  InetSocketAddress getRemoteAddress();
+  SocketAddress getRemoteAddress();
 
   /**
    * Returns the hostname that the user entered into the client, if applicable.

api/src/main/java/com/velocitypowered/api/proxy/Player.java

@@ -31,7 +31,6 @@ import net.kyori.adventure.text.Component;
 import net.kyori.adventure.text.event.HoverEvent;
 import net.kyori.adventure.text.event.HoverEventSource;
 import org.checkerframework.checker.nullness.qual.Nullable;
-import org.checkerframework.checker.nullness.qual.Nullable;
 import org.jetbrains.annotations.NotNull;
 
 /**

api/src/main/java/com/velocitypowered/api/proxy/ProxyServer.java

@@ -18,7 +18,7 @@ import com.velocitypowered.api.proxy.server.RegisteredServer;
 import com.velocitypowered.api.proxy.server.ServerInfo;
 import com.velocitypowered.api.scheduler.Scheduler;
 import com.velocitypowered.api.util.ProxyVersion;
-import java.net.InetSocketAddress;
+import java.net.SocketAddress;
 import java.util.Collection;
 import java.util.Optional;
 import java.util.UUID;
@@ -179,7 +179,7 @@ public interface ProxyServer extends Audience {
    *
    * @return the address the proxy is bound to
    */
-  InetSocketAddress getBoundAddress();
+  SocketAddress getBoundAddress();
 
   /**
    * Gets the {@link ProxyConfig} instance.

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

@@ -8,7 +8,7 @@
 package com.velocitypowered.api.proxy.server;
 
 import com.google.common.base.Preconditions;
-import java.net.InetSocketAddress;
+import java.net.SocketAddress;
 import java.util.Objects;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
@@ -19,7 +19,7 @@ import org.checkerframework.checker.nullness.qual.Nullable;
 public final class ServerInfo implements Comparable<ServerInfo> {
 
   private final String name;
-  private final InetSocketAddress address;
+  private final SocketAddress address;
 
   /**
    * Creates a new ServerInfo object.
@@ -27,7 +27,7 @@ public final class ServerInfo implements Comparable<ServerInfo> {
    * @param name the name for the server
    * @param address the address of the server to connect to
    */
-  public ServerInfo(String name, InetSocketAddress address) {
+  public ServerInfo(String name, SocketAddress address) {
     this.name = Preconditions.checkNotNull(name, "name");
     this.address = Preconditions.checkNotNull(address, "address");
   }
@@ -36,7 +36,7 @@ public final class ServerInfo implements Comparable<ServerInfo> {
     return name;
   }
 
-  public final InetSocketAddress getAddress() {
+  public final SocketAddress getAddress() {
     return address;
   }
 

proxy/src/main/java/com/velocitypowered/proxy/VelocityServer.java

@@ -70,6 +70,7 @@ import io.netty.channel.EventLoopGroup;
 import java.io.IOException;
 import java.io.InputStream;
 import java.net.InetSocketAddress;
+import java.net.SocketAddress;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.security.KeyPair;
@@ -231,16 +232,18 @@ public class VelocityServer implements ProxyServer, ForwardingAudience {
     // init console permissions after plugins are loaded
     console.setupPermissions();
 
+    final SocketAddress bindAddr = configuration.getBind();
     final Integer port = this.options.getPort();
-    if (port != null) {
+    if (port != null && bindAddr instanceof InetSocketAddress) {
       logger.debug("Overriding bind port to {} from command line option", port);
-      this.cm.bind(new InetSocketAddress(configuration.getBind().getHostString(), port));
+      this.cm.bind(new InetSocketAddress(((InetSocketAddress) bindAddr).getHostString(), port));
     } else {
       this.cm.bind(configuration.getBind());
     }
 
-    if (configuration.isQueryEnabled()) {
-      this.cm.queryBind(configuration.getBind().getHostString(), configuration.getQueryPort());
+    if (configuration.isQueryEnabled() && bindAddr instanceof InetSocketAddress) {
+      this.cm.queryBind(((InetSocketAddress) bindAddr).getHostString(),
+          configuration.getQueryPort());
     }
 
     Metrics.VelocityMetrics.startMetrics(this, configuration.getMetrics());
@@ -362,8 +365,8 @@ public class VelocityServer implements ProxyServer, ForwardingAudience {
     logger.info("Loaded {} plugins", pluginManager.getPlugins().size());
   }
 
-  public Bootstrap createBootstrap(@Nullable EventLoopGroup group) {
-    return this.cm.createWorker(group);
+  public Bootstrap createBootstrap(@Nullable EventLoopGroup group, SocketAddress target) {
+    return this.cm.createWorker(group, target);
   }
 
   public ChannelInitializer<Channel> getBackendChannelInitializer() {
@@ -443,7 +446,9 @@ public class VelocityServer implements ProxyServer, ForwardingAudience {
     }
 
     // If we have a new bind address, bind to it
-    if (!configuration.getBind().equals(newConfiguration.getBind())) {
+    SocketAddress oldBind = configuration.getBind();
+    SocketAddress newBind = newConfiguration.getBind();
+    if (!configuration.getBind().equals(newBind)) {
       this.cm.bind(newConfiguration.getBind());
       this.cm.close(configuration.getBind());
     }
@@ -451,12 +456,13 @@ public class VelocityServer implements ProxyServer, ForwardingAudience {
     boolean queryPortChanged = newConfiguration.getQueryPort() != configuration.getQueryPort();
     boolean queryAlreadyEnabled = configuration.isQueryEnabled();
     boolean queryEnabled = newConfiguration.isQueryEnabled();
-    if ((!queryEnabled && queryAlreadyEnabled) || queryPortChanged) {
+    if (oldBind instanceof InetSocketAddress
+        && ((!queryEnabled && queryAlreadyEnabled) || queryPortChanged)) {
       this.cm.close(new InetSocketAddress(
-          configuration.getBind().getHostString(), configuration.getQueryPort()));
+          ((InetSocketAddress) oldBind).getHostString(), configuration.getQueryPort()));
     }
-    if (queryEnabled && queryPortChanged) {
-      this.cm.queryBind(newConfiguration.getBind().getHostString(),
+    if (queryEnabled && queryPortChanged && configuration.getBind() instanceof InetSocketAddress) {
+      this.cm.queryBind(((InetSocketAddress) newConfiguration.getBind()).getHostString(),
           newConfiguration.getQueryPort());
     }
 
@@ -718,7 +724,7 @@ public class VelocityServer implements ProxyServer, ForwardingAudience {
   }
 
   @Override
-  public InetSocketAddress getBoundAddress() {
+  public SocketAddress getBoundAddress() {
     if (configuration == null) {
       throw new IllegalStateException(
           "No configuration"); // even though you'll never get the chance... heh, heh

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

@@ -32,7 +32,7 @@ import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 import java.io.File;
 import java.io.IOException;
 import java.io.InputStream;
-import java.net.InetSocketAddress;
+import java.net.SocketAddress;
 import java.net.URL;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
@@ -247,7 +247,7 @@ public class VelocityConfiguration implements ProxyConfig {
     }
   }
 
-  public InetSocketAddress getBind() {
+  public SocketAddress getBind() {
     return AddressUtil.parseAndResolveAddress(bind);
   }
 

proxy/src/main/java/com/velocitypowered/proxy/connection/backend/BungeeCordMessageResponder.java

@@ -35,6 +35,9 @@ import com.velocitypowered.proxy.server.VelocityRegisteredServer;
 import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.Unpooled;
+import io.netty.channel.unix.DomainSocketAddress;
+import java.net.InetSocketAddress;
+import java.net.SocketAddress;
 import java.util.Optional;
 import java.util.StringJoiner;
 import net.kyori.adventure.identity.Identity;
@@ -94,8 +97,16 @@ public class BungeeCordMessageResponder {
     ByteBuf buf = Unpooled.buffer();
     ByteBufDataOutput out = new ByteBufDataOutput(buf);
     out.writeUTF("IP");
-    out.writeUTF(player.getRemoteAddress().getHostString());
-    out.writeInt(player.getRemoteAddress().getPort());
+
+    SocketAddress address = player.getRemoteAddress();
+    if (address instanceof InetSocketAddress) {
+      InetSocketAddress serverInetAddr = (InetSocketAddress) address;
+      out.writeUTF(serverInetAddr.getHostString());
+      out.writeInt(serverInetAddr.getPort());
+    } else {
+      out.writeUTF("unix://" + ((DomainSocketAddress) address).path());
+      out.writeInt(0);
+    }
     sendResponseOnConnection(buf);
   }
 
@@ -234,8 +245,15 @@ public class BungeeCordMessageResponder {
 
       out.writeUTF("IPOther");
       out.writeUTF(player.getUsername());
-      out.writeUTF(player.getRemoteAddress().getHostString());
-      out.writeInt(player.getRemoteAddress().getPort());
+      SocketAddress address = player.getRemoteAddress();
+      if (address instanceof InetSocketAddress) {
+        InetSocketAddress serverInetAddr = (InetSocketAddress) address;
+        out.writeUTF(serverInetAddr.getHostString());
+        out.writeInt(serverInetAddr.getPort());
+      } else {
+        out.writeUTF("unix://" + ((DomainSocketAddress) address).path());
+        out.writeInt(0);
+      }
 
       sendResponseOnConnection(buf);
     });
@@ -248,8 +266,15 @@ public class BungeeCordMessageResponder {
 
       out.writeUTF("ServerIP");
       out.writeUTF(info.getServerInfo().getName());
-      out.writeUTF(info.getServerInfo().getAddress().getHostString());
-      out.writeShort(info.getServerInfo().getAddress().getPort());
+      SocketAddress address = info.getServerInfo().getAddress();
+      if (address instanceof InetSocketAddress) {
+        InetSocketAddress serverInetAddr = (InetSocketAddress) address;
+        out.writeUTF(serverInetAddr.getHostString());
+        out.writeShort(serverInetAddr.getPort());
+      } else {
+        out.writeUTF("unix://" + ((DomainSocketAddress) address).path());
+        out.writeShort(0);
+      }
 
       sendResponseOnConnection(buf);
     });

proxy/src/main/java/com/velocitypowered/proxy/connection/backend/VelocityServerConnection.java

@@ -45,6 +45,8 @@ import com.velocitypowered.proxy.server.VelocityRegisteredServer;
 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.Unpooled;
 import io.netty.channel.ChannelFutureListener;
+import java.net.InetSocketAddress;
+import java.net.SocketAddress;
 import java.nio.charset.StandardCharsets;
 import java.util.HashMap;
 import java.util.List;
@@ -98,9 +100,10 @@ public class VelocityServerConnection implements MinecraftConnectionAssociation,
     CompletableFuture<Impl> result = new CompletableFuture<>();
     // Note: we use the event loop for the connection the player is on. This reduces context
     // switches.
-    server.createBootstrap(proxyPlayer.getConnection().eventLoop())
+    SocketAddress destinationAddress = registeredServer.getServerInfo().getAddress();
+    server.createBootstrap(proxyPlayer.getConnection().eventLoop(), destinationAddress)
         .handler(server.getBackendChannelInitializer())
-        .connect(registeredServer.getServerInfo().getAddress())
+        .connect(destinationAddress)
         .addListener((ChannelFutureListener) future -> {
           if (future.isSuccess()) {
             connection = new MinecraftConnection(future.channel(), server);
@@ -124,23 +127,37 @@ public class VelocityServerConnection implements MinecraftConnectionAssociation,
   }
 
   String getPlayerRemoteAddressAsString() {
-    final String addr = proxyPlayer.getRemoteAddress().getAddress().getHostAddress();
-    int ipv6ScopeIdx = addr.indexOf('%');
-    if (ipv6ScopeIdx == -1) {
-      return addr;
-    } else {
-      return addr.substring(0, ipv6ScopeIdx);
+    final SocketAddress address = proxyPlayer.getRemoteAddress();
+    if (!(address instanceof InetSocketAddress)) {
+      return address.toString();
     }
+    final String host = ((InetSocketAddress) address).getAddress().getHostAddress();
+    int ipv6ScopeIdx = host.indexOf('%');
+    if (ipv6ScopeIdx == -1) {
+      return host;
+    }
+    return host.substring(0, ipv6ScopeIdx);
+  }
+
+  private String getHandshakeRemoteAddress() {
+    return proxyPlayer.getVirtualHost()
+        .map(InetSocketAddress::getHostString)
+        .or(() -> Optional.of(registeredServer.getServerInfo().getAddress())
+            .filter(addr -> addr instanceof InetSocketAddress)
+            .map(addr -> ((InetSocketAddress) addr).getHostString()))
+        .orElse("");
   }
 
   private String createLegacyForwardingAddress(UnaryOperator<List<Property>> propertiesTransform) {
     // BungeeCord IP forwarding is simply a special injection after the "address" in the handshake,
     // separated by \0 (the null byte). In order, you send the original host, the player's IP, their
     // UUID (undashed), and if you are in online-mode, their login properties (from Mojang).
+    SocketAddress playerRemoteAddress = proxyPlayer.getRemoteAddress();
+    if (!(playerRemoteAddress instanceof InetSocketAddress)) {
+      return getHandshakeRemoteAddress();
+    }
     StringBuilder data = new StringBuilder()
-        .append(proxyPlayer.getVirtualHost()
-            .orElseGet(() -> registeredServer.getServerInfo().getAddress())
-            .getHostString())
+        .append(getHandshakeRemoteAddress())
         .append('\0')
         .append(getPlayerRemoteAddressAsString())
         .append('\0')
@@ -171,10 +188,6 @@ public class VelocityServerConnection implements MinecraftConnectionAssociation,
 
     // Initiate the handshake.
     ProtocolVersion protocolVersion = proxyPlayer.getConnection().getProtocolVersion();
-    String playerVhost = proxyPlayer.getVirtualHost()
-        .orElseGet(() -> registeredServer.getServerInfo().getAddress())
-        .getHostString();
-
     Handshake handshake = new Handshake();
     handshake.setNextStatus(StateRegistry.LOGIN_ID);
     handshake.setProtocolVersion(protocolVersion);
@@ -184,12 +197,15 @@ public class VelocityServerConnection implements MinecraftConnectionAssociation,
       byte[] secret = server.getConfiguration().getForwardingSecret();
       handshake.setServerAddress(createBungeeGuardForwardingAddress(secret));
     } else if (proxyPlayer.getConnection().getType() == ConnectionTypes.LEGACY_FORGE) {
-      handshake.setServerAddress(playerVhost + HANDSHAKE_HOSTNAME_TOKEN);
+      handshake.setServerAddress(getHandshakeRemoteAddress() + HANDSHAKE_HOSTNAME_TOKEN);
     } else {
-      handshake.setServerAddress(playerVhost);
+      handshake.setServerAddress(getHandshakeRemoteAddress());
     }
 
-    handshake.setPort(registeredServer.getServerInfo().getAddress().getPort());
+    SocketAddress destinationAddr = registeredServer.getServerInfo().getAddress();
+    if (destinationAddr instanceof InetSocketAddress) {
+      handshake.setPort(((InetSocketAddress) destinationAddr).getPort());
+    }
     mc.delayedWrite(handshake);
 
     mc.setProtocolVersion(protocolVersion);

proxy/src/main/java/com/velocitypowered/proxy/connection/client/ConnectedPlayer.java

@@ -81,6 +81,7 @@ import com.velocitypowered.proxy.util.collect.CappedSet;
 import io.netty.buffer.ByteBufUtil;
 import io.netty.buffer.Unpooled;
 import java.net.InetSocketAddress;
+import java.net.SocketAddress;
 import java.util.ArrayDeque;
 import java.util.Collection;
 import java.util.Collections;
@@ -304,8 +305,8 @@ public class ConnectedPlayer implements MinecraftConnectionAssociation, Player,
   }
 
   @Override
-  public InetSocketAddress getRemoteAddress() {
-    return (InetSocketAddress) connection.getRemoteAddress();
+  public SocketAddress getRemoteAddress() {
+    return connection.getRemoteAddress();
   }
 
   @Override

proxy/src/main/java/com/velocitypowered/proxy/network/ConnectionManager.java

@@ -38,6 +38,7 @@ import io.netty.channel.WriteBufferWaterMark;
 import io.netty.channel.epoll.EpollChannelOption;
 import io.netty.util.concurrent.GlobalEventExecutor;
 import java.net.InetSocketAddress;
+import java.net.SocketAddress;
 import java.util.HashMap;
 import java.util.Map;
 import org.apache.logging.log4j.LogManager;
@@ -57,7 +58,7 @@ public final class ConnectionManager {
   private static final WriteBufferWaterMark SERVER_WRITE_MARK = new WriteBufferWaterMark(1 << 20,
       1 << 21);
   private static final Logger LOGGER = LogManager.getLogger(ConnectionManager.class);
-  private final Map<InetSocketAddress, Endpoint> endpoints = new HashMap<>();
+  private final Map<SocketAddress, Endpoint> endpoints = new HashMap<>();
   private final TransportType transportType;
   private final EventLoopGroup bossGroup;
   private final EventLoopGroup workerGroup;
@@ -113,18 +114,20 @@ public final class ConnectionManager {
    *
    * @param address the address to bind to
    */
-  public void bind(final InetSocketAddress address) {
+  public void bind(final SocketAddress address) {
     final ServerBootstrap bootstrap = new ServerBootstrap()
-        .channelFactory(this.transportType.serverSocketChannelFactory)
+        .channelFactory(this.transportType.getServerChannelFactory(address))
         .group(this.bossGroup, this.workerGroup)
         .childOption(ChannelOption.WRITE_BUFFER_WATER_MARK, SERVER_WRITE_MARK)
         .childHandler(this.serverChannelInitializer.get())
-        .childOption(ChannelOption.TCP_NODELAY, true)
-        .childOption(ChannelOption.IP_TOS, 0x18)
         .localAddress(address);
 
-    if (transportType == TransportType.EPOLL && server.getConfiguration().useTcpFastOpen()) {
-      bootstrap.option(EpollChannelOption.TCP_FASTOPEN, 3);
+    if (address instanceof InetSocketAddress) {
+      bootstrap.childOption(ChannelOption.TCP_NODELAY, true)
+          .childOption(ChannelOption.IP_TOS, 0x18);
+      if (transportType == TransportType.EPOLL && server.getConfiguration().useTcpFastOpen()) {
+        bootstrap.option(EpollChannelOption.TCP_FASTOPEN, 3);
+      }
     }
 
     bootstrap.bind()
@@ -173,14 +176,15 @@ public final class ConnectionManager {
   }
 
   /**
-   * Creates a TCP {@link Bootstrap} using Velocity's event loops.
+   * Creates a {@link Bootstrap} using Velocity's event loops.
    *
    * @param group the event loop group to use. Use {@code null} for the default worker group.
+   * @param target the address the client will connect to
    * @return a new {@link Bootstrap}
    */
-  public Bootstrap createWorker(@Nullable EventLoopGroup group) {
+  public Bootstrap createWorker(@Nullable EventLoopGroup group, SocketAddress target) {
     Bootstrap bootstrap = new Bootstrap()
-        .channelFactory(this.transportType.socketChannelFactory)
+        .channelFactory(this.transportType.getClientChannelFactory(target))
         .option(ChannelOption.TCP_NODELAY, true)
         .option(ChannelOption.CONNECT_TIMEOUT_MILLIS,
             this.server.getConfiguration().getConnectTimeout())
@@ -197,7 +201,7 @@ public final class ConnectionManager {
    *
    * @param oldBind the endpoint to close
    */
-  public void close(InetSocketAddress oldBind) {
+  public void close(SocketAddress oldBind) {
     Endpoint endpoint = endpoints.remove(oldBind);
 
     // Fire proxy close event to notify plugins of socket close. We block since plugins
@@ -215,8 +219,8 @@ public final class ConnectionManager {
    * Closes all endpoints.
    */
   public void shutdown() {
-    for (final Map.Entry<InetSocketAddress, Endpoint> entry : this.endpoints.entrySet()) {
-      final InetSocketAddress address = entry.getKey();
+    for (final Map.Entry<SocketAddress, Endpoint> entry : this.endpoints.entrySet()) {
+      final SocketAddress address = entry.getKey();
       final Endpoint endpoint = entry.getValue();
 
       // Fire proxy close event to notify plugins of socket close. We block since plugins

proxy/src/main/java/com/velocitypowered/proxy/network/TransportType.java

@@ -18,11 +18,15 @@
 package com.velocitypowered.proxy.network;
 
 import com.velocitypowered.proxy.util.concurrent.VelocityNettyThreadFactory;
+import io.netty.channel.Channel;
 import io.netty.channel.ChannelFactory;
 import io.netty.channel.EventLoopGroup;
+import io.netty.channel.ServerChannel;
 import io.netty.channel.epoll.Epoll;
 import io.netty.channel.epoll.EpollDatagramChannel;
+import io.netty.channel.epoll.EpollDomainSocketChannel;
 import io.netty.channel.epoll.EpollEventLoopGroup;
+import io.netty.channel.epoll.EpollServerDomainSocketChannel;
 import io.netty.channel.epoll.EpollServerSocketChannel;
 import io.netty.channel.epoll.EpollSocketChannel;
 import io.netty.channel.nio.NioEventLoopGroup;
@@ -32,6 +36,10 @@ import io.netty.channel.socket.SocketChannel;
 import io.netty.channel.socket.nio.NioDatagramChannel;
 import io.netty.channel.socket.nio.NioServerSocketChannel;
 import io.netty.channel.socket.nio.NioSocketChannel;
+import io.netty.channel.unix.DomainSocketAddress;
+import io.netty.channel.unix.DomainSocketChannel;
+import io.netty.channel.unix.ServerDomainSocketChannel;
+import java.net.SocketAddress;
 import java.util.concurrent.ThreadFactory;
 import java.util.function.BiFunction;
 
@@ -42,27 +50,37 @@ public enum TransportType {
   NIO("NIO", NioServerSocketChannel::new,
       NioSocketChannel::new,
       NioDatagramChannel::new,
+      null,
+      null,
       (name, type) -> new NioEventLoopGroup(0, createThreadFactory(name, type))),
   EPOLL("epoll", EpollServerSocketChannel::new,
       EpollSocketChannel::new,
       EpollDatagramChannel::new,
+      EpollServerDomainSocketChannel::new,
+      EpollDomainSocketChannel::new,
       (name, type) -> new EpollEventLoopGroup(0, createThreadFactory(name, type)));
 
   final String name;
   final ChannelFactory<? extends ServerSocketChannel> serverSocketChannelFactory;
   final ChannelFactory<? extends SocketChannel> socketChannelFactory;
   final ChannelFactory<? extends DatagramChannel> datagramChannelFactory;
+  final ChannelFactory<? extends ServerDomainSocketChannel> domainServerSocketChannelFactory;
+  final ChannelFactory<? extends DomainSocketChannel> domainSocketChannelFactory;
   final BiFunction<String, Type, EventLoopGroup> eventLoopGroupFactory;
 
   TransportType(final String name,
       final ChannelFactory<? extends ServerSocketChannel> serverSocketChannelFactory,
       final ChannelFactory<? extends SocketChannel> socketChannelFactory,
       final ChannelFactory<? extends DatagramChannel> datagramChannelFactory,
+      final ChannelFactory<? extends ServerDomainSocketChannel> domainServerSocketChannelFactory,
+      final ChannelFactory<? extends DomainSocketChannel> domainSocketChannelFactory,
       final BiFunction<String, Type, EventLoopGroup> eventLoopGroupFactory) {
     this.name = name;
     this.serverSocketChannelFactory = serverSocketChannelFactory;
     this.socketChannelFactory = socketChannelFactory;
     this.datagramChannelFactory = datagramChannelFactory;
+    this.domainServerSocketChannelFactory = domainServerSocketChannelFactory;
+    this.domainSocketChannelFactory = domainSocketChannelFactory;
     this.eventLoopGroupFactory = eventLoopGroupFactory;
   }
 
@@ -71,6 +89,40 @@ public enum TransportType {
     return this.name;
   }
 
+  /**
+   * Returns the channel factory to use to listen on the specified socket address.
+   *
+   * @param address the address we want to listen on
+   * @return the channel factory
+   */
+  public ChannelFactory<? extends ServerChannel> getServerChannelFactory(SocketAddress address) {
+    if (address instanceof DomainSocketAddress) {
+      if (this.domainServerSocketChannelFactory == null) {
+        throw new IllegalArgumentException(
+            "Domain sockets are not available for non-Linux platforms");
+      }
+      return this.domainServerSocketChannelFactory;
+    }
+    return this.serverSocketChannelFactory;
+  }
+
+  /**
+   * Returns the channel factory to use to connect on the specified socket address.
+   *
+   * @param address the address we want to connect to
+   * @return the channel factory
+   */
+  public ChannelFactory<? extends Channel> getClientChannelFactory(SocketAddress address) {
+    if (address instanceof DomainSocketAddress) {
+      if (this.domainSocketChannelFactory == null) {
+        throw new IllegalArgumentException(
+            "Domain sockets are not available for non-Linux platforms");
+      }
+      return this.domainSocketChannelFactory;
+    }
+    return this.socketChannelFactory;
+  }
+
   public EventLoopGroup createEventLoopGroup(final Type type) {
     return this.eventLoopGroupFactory.apply(this.name, type);
   }

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

@@ -35,6 +35,7 @@ import io.netty.channel.ChannelHandlerContext;
 import io.netty.channel.SimpleChannelInboundHandler;
 import io.netty.channel.socket.DatagramPacket;
 import java.net.InetAddress;
+import java.net.InetSocketAddress;
 import java.nio.charset.StandardCharsets;
 import java.security.SecureRandom;
 import java.util.ArrayList;
@@ -92,8 +93,8 @@ public class GameSpyQueryHandler extends SimpleChannelInboundHandler<DatagramPac
         .map(server.getConfiguration().getQueryMap())
         .currentPlayers(server.getPlayerCount())
         .maxPlayers(server.getConfiguration().getShowMaxPlayers())
-        .proxyPort(server.getConfiguration().getBind().getPort())
-        .proxyHost(server.getConfiguration().getBind().getHostString())
+        .proxyPort(((InetSocketAddress) server.getConfiguration().getBind()).getPort())
+        .proxyHost(((InetSocketAddress) server.getConfiguration().getBind()).getHostString())
         .players(server.getAllPlayers().stream().map(Player::getUsername)
             .collect(Collectors.toList()))
         .proxyVersion("Velocity")

proxy/src/main/java/com/velocitypowered/proxy/server/PingSessionHandler.java

@@ -29,6 +29,8 @@ import com.velocitypowered.proxy.protocol.packet.StatusRequest;
 import com.velocitypowered.proxy.protocol.packet.StatusResponse;
 import io.netty.channel.EventLoop;
 import java.io.IOException;
+import java.net.InetSocketAddress;
+import java.net.SocketAddress;
 import java.util.concurrent.CompletableFuture;
 
 /**
@@ -55,8 +57,16 @@ public class PingSessionHandler implements MinecraftSessionHandler {
   public void activated() {
     Handshake handshake = new Handshake();
     handshake.setNextStatus(StateRegistry.STATUS_ID);
-    handshake.setServerAddress(server.getServerInfo().getAddress().getHostString());
-    handshake.setPort(server.getServerInfo().getAddress().getPort());
+
+    SocketAddress address = server.getServerInfo().getAddress();
+    if (address instanceof InetSocketAddress) {
+      InetSocketAddress socketAddr = (InetSocketAddress) address;
+      handshake.setServerAddress(socketAddr.getHostString());
+      handshake.setPort(socketAddr.getPort());
+    } else {
+      // Just fake it
+      handshake.setServerAddress("127.0.0.1");
+    }
     handshake.setProtocolVersion(version);
     connection.delayedWrite(handshake);
 

proxy/src/main/java/com/velocitypowered/proxy/server/VelocityRegisteredServer.java

@@ -106,7 +106,7 @@ public class VelocityRegisteredServer implements RegisteredServer, ForwardingAud
       throw new IllegalStateException("No Velocity proxy instance available");
     }
     CompletableFuture<ServerPing> pingFuture = new CompletableFuture<>();
-    server.createBootstrap(loop)
+    server.createBootstrap(loop, serverInfo.getAddress())
         .handler(new ChannelInitializer<Channel>() {
           @Override
           protected void initChannel(Channel ch) throws Exception {

proxy/src/main/java/com/velocitypowered/proxy/util/AddressUtil.java

@@ -19,8 +19,11 @@ package com.velocitypowered.proxy.util;
 
 import com.google.common.base.Preconditions;
 import com.google.common.net.InetAddresses;
+import io.netty.channel.epoll.Epoll;
+import io.netty.channel.unix.DomainSocketAddress;
 import java.net.InetAddress;
 import java.net.InetSocketAddress;
+import java.net.SocketAddress;
 import java.net.URI;
 
 /**
@@ -35,14 +38,16 @@ public final class AddressUtil {
   }
 
   /**
-   * Attempts to parse an IP address of the form {@code 127.0.0.1:25565}. The returned
-   * {@link InetSocketAddress} is not resolved.
+   * Attempts to parse a socket address of the form {@code 127.0.0.1:25565}. The returned
+   * {@link SocketAddress} is not resolved if it is a {@link InetSocketAddress}.
    *
    * @param ip the IP to parse
    * @return the parsed address
    */
-  public static InetSocketAddress parseAddress(String ip) {
-    Preconditions.checkNotNull(ip, "ip");
+  public static SocketAddress parseAddress(String ip) {
+    if (ip.startsWith("unix://") && Epoll.isAvailable()) {
+      return new DomainSocketAddress(ip.substring("unix://".length()));
+    }
     URI uri = URI.create("tcp://" + ip);
     if (uri.getHost() == null) {
       throw new IllegalStateException("Invalid hostname/IP " + ip);
@@ -58,13 +63,16 @@ public final class AddressUtil {
   }
 
   /**
-   * Attempts to parse an IP address of the form {@code 127.0.0.1:25565}. The returned
-   * {@link InetSocketAddress} is resolved.
+   * Attempts to parse a socket address of the form {@code 127.0.0.1:25565}. The returned
+   * {@link SocketAddress} is resolved if it is a {@link InetSocketAddress}.
    *
    * @param ip the IP to parse
    * @return the parsed address
    */
-  public static InetSocketAddress parseAndResolveAddress(String ip) {
+  public static SocketAddress parseAndResolveAddress(String ip) {
+    if (ip.startsWith("unix://") && Epoll.isAvailable()) {
+      return new DomainSocketAddress(ip.substring("unix://".length()));
+    }
     Preconditions.checkNotNull(ip, "ip");
     URI uri = URI.create("tcp://" + ip);
     if (uri.getHost() == null) {

proxy/src/main/java/com/velocitypowered/proxy/util/InformationUtils.java

@@ -38,6 +38,7 @@ import java.net.Inet4Address;
 import java.net.Inet6Address;
 import java.net.InetAddress;
 import java.net.InetSocketAddress;
+import java.net.SocketAddress;
 import java.util.List;
 import java.util.Map;
 
@@ -196,14 +197,19 @@ public enum InformationUtils {
   public static JsonObject collectServerInfo(RegisteredServer server) {
     JsonObject info = new JsonObject();
     info.addProperty("currentPlayers", server.getPlayersConnected().size());
-    InetSocketAddress iaddr = server.getServerInfo().getAddress();
-    if (iaddr.isUnresolved()) {
-      // Greetings form Netty 4aa10db9
-      info.addProperty("host", iaddr.getHostString());
+    SocketAddress addr = server.getServerInfo().getAddress();
+    if (addr instanceof InetSocketAddress) {
+      InetSocketAddress iaddr = (InetSocketAddress) addr;
+      if (iaddr.isUnresolved()) {
+        // Greetings form Netty 4aa10db9
+        info.addProperty("host", iaddr.getHostString());
+      } else {
+        info.addProperty("host", anonymizeInetAddress(iaddr.getAddress()));
+      }
+      info.addProperty("port", iaddr.getPort());
     } else {
-      info.addProperty("host", anonymizeInetAddress(iaddr.getAddress()));
+      info.addProperty("bind", addr.toString());
     }
-    info.addProperty("port", iaddr.getPort());
     return info;
   }