Add unix domain socket support

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

@@ -9,6 +9,7 @@
 
 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 +20,7 @@
 public final class ServerInfo implements Comparable<ServerInfo> {
 
   private final String name;
-  private final InetSocketAddress address;
+  private final SocketAddress address;
 
   /**
    * Creates a new ServerInfo object.
@@ -32,11 +33,44 @@ public ServerInfo(String name, InetSocketAddress address) {
     this.address = Preconditions.checkNotNull(address, "address");
   }
 
+  /**
+   * Creates a new ServerInfo object.
+   *
+   * @param name the name for the server
+   * @param address the address of the server to connect to
+   */
+  public ServerInfo(String name, SocketAddress address) {
+    this.name = Preconditions.checkNotNull(name, "name");
+    this.address = Preconditions.checkNotNull(address, "address");
+  }
+
   public final String getName() {
     return name;
   }
 
+  /**
+   * Returns the address of this server as an {@link InetSocketAddress}.
+   *
+   * @return the address
+   * @deprecated Use {@link #getSocketAddress()} instead, which supports both TCP and Unix socket
+   *     addresses.
+   */
+  @Deprecated
   public final InetSocketAddress getAddress() {
+    if (address instanceof InetSocketAddress inet) {
+      return inet;
+    }
+    throw new UnsupportedOperationException(
+        "This server is not configured with an InetSocketAddress. Use getSocketAddress() instead.");
+  }
+
+  /**
+   * Returns the address of this server as a {@link SocketAddress}. This may be an
+   * {@link InetSocketAddress} for TCP connections or a Unix domain socket address.
+   *
+   * @return the address
+   */
+  public final SocketAddress getSocketAddress() {
     return address;
   }
 

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

@@ -20,7 +20,7 @@
 import com.velocitypowered.api.proxy.server.ServerInfo;
 import com.velocitypowered.proxy.util.AddressUtil;
 import java.io.IOException;
-import java.net.InetSocketAddress;
+import java.net.SocketAddress;
 import java.util.Arrays;
 import java.util.List;
 import joptsimple.OptionParser;
@@ -109,7 +109,7 @@ public ServerInfo convert(String s) {
       if (split.length < 2) {
         throw new ValueConversionException("Invalid server format. Use <name>:<address>");
       }
-      InetSocketAddress address;
+      SocketAddress address;
       try {
         address = AddressUtil.parseAddress(split[1]);
       } catch (IllegalStateException e) {

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

@@ -78,6 +78,7 @@
 import java.io.InputStream;
 import java.net.InetAddress;
 import java.net.InetSocketAddress;
+import java.net.SocketAddress;
 import java.net.http.HttpClient;
 import java.nio.file.Files;
 import java.nio.file.Path;
@@ -455,8 +456,8 @@ private void loadPlugins() {
     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() {

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

@@ -257,7 +257,7 @@ private void loadFavicon() {
   }
 
   public InetSocketAddress getBind() {
-    return AddressUtil.parseAndResolveAddress(bind);
+    return (InetSocketAddress) AddressUtil.parseAndResolveAddress(bind);
   }
 
   @Override

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

@@ -36,6 +36,9 @@
 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.text.Component;
@@ -247,8 +250,14 @@ private void processServerIp(ByteBufDataInput in) {
 
       out.writeUTF("ServerIP");
       out.writeUTF(info.getServerInfo().getName());
-      out.writeUTF(info.getServerInfo().getAddress().getHostString());
-      out.writeShort(info.getServerInfo().getAddress().getPort());
+      SocketAddress address = info.getServerInfo().getSocketAddress();
+      if (address instanceof InetSocketAddress inetAddr) {
+        out.writeUTF(inetAddr.getHostString());
+        out.writeShort(inetAddr.getPort());
+      } else {
+        out.writeUTF("unix://" + ((DomainSocketAddress) address).path());
+        out.writeShort(0);
+      }
 
       sendResponseOnConnection(buf);
     });

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

@@ -49,6 +49,8 @@
 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.util.HashMap;
 import java.util.Map;
 import java.util.Optional;
@@ -100,9 +102,10 @@ public CompletableFuture<Impl> connect() {
     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().getSocketAddress();
+    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);
@@ -143,17 +146,27 @@ String getPlayerRemoteAddressAsString() {
 
   private String createLegacyForwardingAddress() {
     return PlayerDataForwarding.createLegacyForwardingAddress(
-      proxyPlayer.getVirtualHost().orElseGet(() ->
-        registeredServer.getServerInfo().getAddress()).getHostString(),
+            proxyPlayer.getVirtualHost().orElseGet(() -> {
+              SocketAddress address = registeredServer.getServerInfo().getSocketAddress();
+              if (address instanceof InetSocketAddress inetAddr) {
+                return inetAddr;
+              }
+              return InetSocketAddress.createUnresolved("::", 0);
+            }).getHostString(),
       getPlayerRemoteAddressAsString(),
       proxyPlayer.getGameProfile()
     );
   }
 
   private String createBungeeGuardForwardingAddress(byte[] forwardingSecret) {
     return PlayerDataForwarding.createBungeeGuardForwardingAddress(
-      proxyPlayer.getVirtualHost().orElseGet(() ->
-        registeredServer.getServerInfo().getAddress()).getHostString(),
+      proxyPlayer.getVirtualHost().orElseGet(() -> {
+        SocketAddress address = registeredServer.getServerInfo().getSocketAddress();
+        if (address instanceof InetSocketAddress inetAddr) {
+          return inetAddr;
+        }
+        return InetSocketAddress.createUnresolved("::", 0);
+      }).getHostString(),
       getPlayerRemoteAddressAsString(),
       proxyPlayer.getGameProfile(),
       forwardingSecret
@@ -166,9 +179,13 @@ private void startHandshake() {
 
     // Initiate the handshake.
     ProtocolVersion protocolVersion = proxyPlayer.getConnection().getProtocolVersion();
-    String playerVhost = proxyPlayer.getVirtualHost()
-                .orElseGet(() -> registeredServer.getServerInfo().getAddress())
-                .getHostString();
+    String playerVhost = proxyPlayer.getVirtualHost().orElseGet(() -> {
+      SocketAddress address = registeredServer.getServerInfo().getSocketAddress();
+      if (address instanceof InetSocketAddress inetAddr) {
+        return inetAddr;
+      }
+      return InetSocketAddress.createUnresolved("::", 0);
+    }).getHostString();
 
     HandshakePacket handshake = new HandshakePacket();
     handshake.setIntent(HandshakeIntent.LOGIN);
@@ -186,9 +203,10 @@ private void startHandshake() {
       handshake.setServerAddress(playerVhost);
     }
 
-    handshake.setPort(proxyPlayer.getVirtualHost()
-            .orElseGet(() -> registeredServer.getServerInfo().getAddress())
-            .getPort());
+    SocketAddress destinationAddr = registeredServer.getServerInfo().getSocketAddress();
+    if (destinationAddr instanceof InetSocketAddress) {
+      handshake.setPort(((InetSocketAddress) destinationAddr).getPort());
+    }
     mc.delayedWrite(handshake);
 
     mc.setProtocolVersion(protocolVersion);

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

@@ -35,10 +35,12 @@
 import io.netty.channel.ChannelOption;
 import io.netty.channel.EventLoopGroup;
 import io.netty.channel.WriteBufferWaterMark;
+import io.netty.channel.unix.DomainSocketAddress;
 import io.netty.channel.unix.UnixChannelOption;
 import io.netty.util.concurrent.GlobalEventExecutor;
 import io.netty.util.concurrent.MultithreadEventExecutorGroup;
 import java.net.InetSocketAddress;
+import java.net.SocketAddress;
 import java.net.http.HttpClient;
 import java.util.Collection;
 import java.util.Map;
@@ -184,21 +186,24 @@ public void queryBind(final String hostname, final int port) {
   }
 
   /**
-   * 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)
-        .option(ChannelOption.TCP_NODELAY, true)
+        .channelFactory(this.transportType.getClientChannelFactory(target))
         .option(ChannelOption.CONNECT_TIMEOUT_MILLIS,
             this.server.getConfiguration().getConnectTimeout())
         .group(group == null ? this.workerGroup : group)
         .resolver(this.resolver.asGroup());
-    if (server.getConfiguration().useTcpFastOpen()) {
-      bootstrap.option(ChannelOption.TCP_FASTOPEN_CONNECT, true);
+    if (!(target instanceof DomainSocketAddress)) {
+      bootstrap.option(ChannelOption.TCP_NODELAY, true);
+      if (server.getConfiguration().useTcpFastOpen()) {
+        bootstrap.option(ChannelOption.TCP_FASTOPEN_CONNECT, true);
+      }
     }
     return bootstrap;
   }

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

@@ -18,13 +18,17 @@
 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.IoHandlerFactory;
 import io.netty.channel.MultiThreadIoEventLoopGroup;
+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.EpollIoHandler;
+import io.netty.channel.epoll.EpollServerDomainSocketChannel;
 import io.netty.channel.epoll.EpollServerSocketChannel;
 import io.netty.channel.epoll.EpollSocketChannel;
 import io.netty.channel.kqueue.KQueue;
@@ -39,11 +43,17 @@
 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 io.netty.channel.uring.IoUring;
 import io.netty.channel.uring.IoUringDatagramChannel;
+import io.netty.channel.uring.IoUringDomainSocketChannel;
 import io.netty.channel.uring.IoUringIoHandler;
+import io.netty.channel.uring.IoUringServerDomainSocketChannel;
 import io.netty.channel.uring.IoUringServerSocketChannel;
 import io.netty.channel.uring.IoUringSocketChannel;
+import java.net.SocketAddress;
 import java.util.concurrent.ThreadFactory;
 import java.util.function.Supplier;
 
@@ -54,35 +64,49 @@ public enum TransportType {
   NIO("NIO", NioServerSocketChannel::new,
       NioSocketChannel::new,
       NioDatagramChannel::new,
+      null,
+      null,
       NioIoHandler::newFactory),
   EPOLL("epoll", EpollServerSocketChannel::new,
       EpollSocketChannel::new,
       EpollDatagramChannel::new,
+      EpollServerDomainSocketChannel::new,
+      EpollDomainSocketChannel::new,
       EpollIoHandler::newFactory),
   KQUEUE("kqueue", KQueueServerSocketChannel::new,
       KQueueSocketChannel::new,
       KQueueDatagramChannel::new,
+      null,
+      null,
       KQueueIoHandler::newFactory),
   IO_URING("io_uring", IoUringServerSocketChannel::new,
       IoUringSocketChannel::new,
       IoUringDatagramChannel::new,
+      IoUringServerDomainSocketChannel::new,
+      IoUringDomainSocketChannel::new,
       IoUringIoHandler::newFactory);
 
   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 Supplier<IoHandlerFactory> ioHandlerFactorySupplier;
 
   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 Supplier<IoHandlerFactory> ioHandlerFactorySupplier) {
     this.name = name;
     this.serverSocketChannelFactory = serverSocketChannelFactory;
     this.socketChannelFactory = socketChannelFactory;
     this.datagramChannelFactory = datagramChannelFactory;
+    this.domainServerSocketChannelFactory = domainServerSocketChannelFactory;
+    this.domainSocketChannelFactory = domainSocketChannelFactory;
     this.ioHandlerFactorySupplier = ioHandlerFactorySupplier;
   }
 
@@ -91,6 +115,40 @@ public String toString() {
     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;
+  }
+
   /**
    * Creates a new event loop group for the given type.
    *