Paper/paper-server/patches/sources/net/minecraft/server/network/LegacyQueryHandler.java.patch

--- a/net/minecraft/server/network/LegacyQueryHandler.java
+++ b/net/minecraft/server/network/LegacyQueryHandler.java
@@ -14,6 +_,7 @@
 public class LegacyQueryHandler extends ChannelInboundHandlerAdapter {
     private static final Logger LOGGER = LogUtils.getLogger();
     private final ServerInfo server;
+    private ByteBuf buf; // Paper
 
     public LegacyQueryHandler(ServerInfo server) {
         this.server = server;
@@ -22,6 +_,17 @@
     @Override
     public void channelRead(ChannelHandlerContext context, Object message) {
         ByteBuf byteBuf = (ByteBuf)message;
+        // Paper start - Make legacy ping handler more reliable
+        if (this.buf != null) {
+            try {
+                readLegacy1_6(context, byteBuf);
+            } finally {
+                byteBuf.release();
+            }
+            return;
+        }
+        // Paper end - Make legacy ping handler more reliable
+
         byteBuf.markReaderIndex();
         boolean flag = true;
 
@@ -33,9 +_,19 @@
 
                 SocketAddress socketAddress = context.channel().remoteAddress();
                 int i = byteBuf.readableBytes();
+                String string = null; // Paper
                 if (i == 0) {
-                    LOGGER.debug("Ping: (<1.3.x) from {}", socketAddress);
-                    String string = createVersion0Response(this.server);
+                    LOGGER.debug("Ping: (<1.3.x) from {}", net.minecraft.server.MinecraftServer.getServer().logIPs() ? socketAddress: "<ip address withheld>"); // Paper - Respect logIPs option
+                    // Paper start - Call PaperServerListPingEvent and use results
+                    com.destroystokyo.paper.event.server.PaperServerListPingEvent event = com.destroystokyo.paper.network.PaperLegacyStatusClient.processRequest(net.minecraft.server.MinecraftServer.getServer(), (java.net.InetSocketAddress) socketAddress, 39, null);
+                    if (event == null) {
+                        context.close();
+                        byteBuf.release();
+                        flag = false;
+                        return;
+                    }
+                    string = String.format(Locale.ROOT, "%s§%d§%d", com.destroystokyo.paper.network.PaperLegacyStatusClient.getUnformattedMotd(event), event.getNumPlayers(), event.getMaxPlayers());
+                    // Paper end - Call PaperServerListPingEvent and use results
                     sendFlushAndClose(context, createLegacyDisconnectPacket(context.alloc(), string));
                 } else {
                     if (byteBuf.readUnsignedByte() != 1) {
@@ -43,16 +_,39 @@
                     }
 
                     if (byteBuf.isReadable()) {
-                        if (!readCustomPayloadPacket(byteBuf)) {
+                        // Paper start - Replace below
+                        if (byteBuf.readUnsignedByte() != LegacyProtocolUtils.CUSTOM_PAYLOAD_PACKET_ID) {
+                            string = this.readLegacy1_6(context, byteBuf);
+                            if (string == null) {
+                                return;
+                            }
+                        }
+                        // Paper end - Replace below
+                    } else {
+                        LOGGER.debug("Ping: (1.4-1.5.x) from {}", net.minecraft.server.MinecraftServer.getServer().logIPs() ? socketAddress : "<ip address withheld>"); // Paper - Respect logIPs option
+                    }
+
+                    // Paper start - Call PaperServerListPingEvent and use results
+                    if (string == null) {
+                        com.destroystokyo.paper.event.server.PaperServerListPingEvent event = com.destroystokyo.paper.network.PaperLegacyStatusClient.processRequest(net.minecraft.server.MinecraftServer.getServer(), (java.net.InetSocketAddress) socketAddress, 127, null); // Paper
+                        if (event == null) {
+                            context.close();
+                            byteBuf.release();
+                            flag = false;
                             return;
                         }
 
-                        LOGGER.debug("Ping: (1.6) from {}", socketAddress);
-                    } else {
-                        LOGGER.debug("Ping: (1.4-1.5.x) from {}", socketAddress);
+                        // See createVersion1Response
+                        string = String.format(
+                            Locale.ROOT,
+                            "§1\u0000%d\u0000%s\u0000%s\u0000%d\u0000%d",
+                            event.getProtocolVersion(), this.server.getServerVersion(),
+                            event.getMotd(),
+                            event.getNumPlayers(),
+                            event.getMaxPlayers()
+                        );
+                        // Paper end - Call PaperServerListPingEvent and use results
                     }
-
-                    String string = createVersion1Response(this.server);
                     sendFlushAndClose(context, createLegacyDisconnectPacket(context.alloc(), string));
                 }
 
@@ -110,6 +_,98 @@
             server.getMaxPlayers()
         );
     }
+
+    // Paper start
+    private static String readLegacyString(ByteBuf buf) {
+        int size = buf.readShort() * Character.BYTES;
+        if (!buf.isReadable(size)) {
+            return null;
+        }
+
+        String result = buf.toString(buf.readerIndex(), size, java.nio.charset.StandardCharsets.UTF_16BE);
+        buf.skipBytes(size); // toString doesn't increase readerIndex automatically
+        return result;
+    }
+
+    private String readLegacy1_6(ChannelHandlerContext ctx, ByteBuf part) {
+        ByteBuf buf = this.buf;
+
+        if (buf == null) {
+            this.buf = buf = ctx.alloc().buffer();
+            buf.markReaderIndex();
+        } else {
+            buf.resetReaderIndex();
+        }
+
+        buf.writeBytes(part);
+
+        if (!buf.isReadable(Short.BYTES + Short.BYTES + Byte.BYTES + Short.BYTES + Integer.BYTES)) {
+            return null;
+        }
+
+        String string = readLegacyString(buf);
+        if (string == null) {
+            return null;
+        }
+
+        if (!string.equals(LegacyProtocolUtils.CUSTOM_PAYLOAD_PACKET_PING_CHANNEL)) {
+            removeHandler(ctx);
+            return null;
+        }
+
+        if (!buf.isReadable(Short.BYTES) || !buf.isReadable(buf.readShort())) {
+            return null;
+        }
+
+        int protocolVersion = buf.readByte();
+        String host = readLegacyString(buf);
+        if (host == null) {
+            removeHandler(ctx);
+            return null;
+        }
+
+        int port = buf.readInt();
+        if (buf.isReadable()) {
+            removeHandler(ctx);
+            return null;
+        }
+
+        buf.release();
+        this.buf = null;
+
+        LOGGER.debug("Ping: (1.6) from {}", net.minecraft.server.MinecraftServer.getServer().logIPs() ? ctx.channel().remoteAddress(): "<ip address withheld>"); // Paper - Respect logIPs option
+
+        net.minecraft.server.MinecraftServer server = net.minecraft.server.MinecraftServer.getServer();
+        java.net.InetSocketAddress virtualHost = com.destroystokyo.paper.network.PaperNetworkClient.prepareVirtualHost(host, port);
+        com.destroystokyo.paper.event.server.PaperServerListPingEvent event = com.destroystokyo.paper.network.PaperLegacyStatusClient.processRequest(
+            server, (java.net.InetSocketAddress) ctx.channel().remoteAddress(), protocolVersion, virtualHost);
+        if (event == null) {
+            ctx.close();
+            return null;
+        }
+
+        String response = String.format("\u00a71\u0000%d\u0000%s\u0000%s\u0000%d\u0000%d", event.getProtocolVersion(), event.getVersion(),
+            com.destroystokyo.paper.network.PaperLegacyStatusClient.getMotd(event), event.getNumPlayers(), event.getMaxPlayers());
+        return response;
+    }
+
+    private void removeHandler(ChannelHandlerContext ctx) {
+        ByteBuf buf = this.buf;
+        this.buf = null;
+
+        buf.resetReaderIndex();
+        ctx.pipeline().remove(this);
+        ctx.fireChannelRead(buf);
+    }
+
+    @Override
+    public void handlerRemoved(ChannelHandlerContext ctx) {
+        if (this.buf != null) {
+            this.buf.release();
+            this.buf = null;
+        }
+    }
+    // Paper end
 
     private static void sendFlushAndClose(ChannelHandlerContext context, ByteBuf buffer) {
         context.pipeline().firstContext().writeAndFlush(buffer).addListener(ChannelFutureListener.CLOSE);