2018-03-30 19:00:01 +02:00
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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Minecrell <minecrell@minecrell.net>
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Date: Wed, 11 Oct 2017 18:22:50 +0200
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2018-07-13 09:43:56 +02:00
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Subject: [PATCH] Make legacy ping handler more reliable
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2018-03-30 19:00:01 +02:00
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The Minecraft server often fails to respond to old ("legacy") pings
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from old Minecraft versions using the protocol used before the switch
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to Netty in Minecraft 1.7.
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Due to packet fragmentation[1], we might not have all needed bytes
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available when the LegacyPingHandler is called. In this case, it will
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run into an error, remove the handler and continue using the modern
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protocol.
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This is unlikely to happen for the first two revisions of the legacy
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ping protocol (used in Minecraft 1.5.x and older) since the request
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consists of only one or two bytes, but happens frequently for the
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last/third revision introduced in Minecraft 1.6.
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It has much larger, variable packet sizes due to the inclusion of
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the virtual host (the hostname/port used to connect to the server).
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The solution[2] is simple: If we find more than two matching bytes,
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we buffer the remaining bytes until we have enough to fully read and
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respond to the request.
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[1]: https://netty.io/wiki/user-guide-for-4.x.html#wiki-h3-11
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[2]: https://netty.io/wiki/user-guide-for-4.x.html#wiki-h4-13
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diff --git a/src/main/java/net/minecraft/server/LegacyPingHandler.java b/src/main/java/net/minecraft/server/LegacyPingHandler.java
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2020-05-06 11:48:49 +02:00
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index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
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2018-03-30 19:00:01 +02:00
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--- a/src/main/java/net/minecraft/server/LegacyPingHandler.java
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+++ b/src/main/java/net/minecraft/server/LegacyPingHandler.java
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2018-12-17 06:18:06 +01:00
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@@ -0,0 +0,0 @@ public class LegacyPingHandler extends ChannelInboundHandlerAdapter {
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2019-04-28 19:59:47 +02:00
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private static final Logger LOGGER = LogManager.getLogger();
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2018-03-30 19:00:01 +02:00
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private final ServerConnection b;
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+ private ByteBuf buf; // Paper
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public LegacyPingHandler(ServerConnection serverconnection) {
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this.b = serverconnection;
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@@ -0,0 +0,0 @@ public class LegacyPingHandler extends ChannelInboundHandlerAdapter {
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public void channelRead(ChannelHandlerContext channelhandlercontext, Object object) throws Exception {
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2018-12-17 06:18:06 +01:00
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ByteBuf bytebuf = (ByteBuf) object;
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2018-03-30 19:00:01 +02:00
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+ // Paper start - Make legacy ping handler more reliable
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+ if (this.buf != null) {
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+ try {
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+ readLegacy1_6(channelhandlercontext, bytebuf);
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+ } finally {
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+ bytebuf.release();
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+ }
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+ return;
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+ }
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+ // Paper end
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bytebuf.markReaderIndex();
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boolean flag = true;
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@@ -0,0 +0,0 @@ public class LegacyPingHandler extends ChannelInboundHandlerAdapter {
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2019-05-28 01:01:45 +02:00
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this.a(channelhandlercontext, this.a(s));
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break;
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default:
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2018-12-17 06:18:06 +01:00
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+ // Paper start - Replace with improved version below
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+ if (bytebuf.readUnsignedByte() != 0x01 || bytebuf.readUnsignedByte() != 0xFA) return;
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+ readLegacy1_6(channelhandlercontext, bytebuf);
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+ /*
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2019-05-28 01:01:45 +02:00
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boolean flag1 = bytebuf.readUnsignedByte() == 1;
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2018-12-17 06:18:06 +01:00
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2019-05-28 01:01:45 +02:00
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flag1 &= bytebuf.readUnsignedByte() == 250;
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2018-03-30 19:00:01 +02:00
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@@ -0,0 +0,0 @@ public class LegacyPingHandler extends ChannelInboundHandlerAdapter {
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2019-05-28 01:01:45 +02:00
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} finally {
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bytebuf1.release();
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}
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2018-12-17 06:18:06 +01:00
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+ */ // Paper end - Replace with improved version below
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}
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2018-03-30 19:00:01 +02:00
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2018-12-17 06:18:06 +01:00
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bytebuf.release();
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2018-03-30 19:00:01 +02:00
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@@ -0,0 +0,0 @@ public class LegacyPingHandler extends ChannelInboundHandlerAdapter {
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}
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+ // Paper start
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2018-07-13 09:43:56 +02:00
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+ private static String readLegacyString(ByteBuf buf) {
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+ int size = buf.readShort() * Character.BYTES;
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+ if (!buf.isReadable(size)) {
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+ return null;
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+ }
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+
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+ String result = buf.toString(buf.readerIndex(), size, StandardCharsets.UTF_16BE);
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+ buf.skipBytes(size); // toString doesn't increase readerIndex automatically
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+ return result;
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+ }
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+
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2018-03-30 19:00:01 +02:00
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+ private void readLegacy1_6(ChannelHandlerContext ctx, ByteBuf part) {
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+ ByteBuf buf = this.buf;
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+
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+ if (buf == null) {
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+ this.buf = buf = ctx.alloc().buffer();
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+ buf.markReaderIndex();
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+ } else {
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+ buf.resetReaderIndex();
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+ }
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+
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+ buf.writeBytes(part);
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+
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2018-07-13 09:43:56 +02:00
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+ if (!buf.isReadable(Short.BYTES + Short.BYTES + Byte.BYTES + Short.BYTES + Integer.BYTES)) {
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2018-03-30 19:00:01 +02:00
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+ return;
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+ }
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+
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2018-07-13 09:43:56 +02:00
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+ String s = readLegacyString(buf);
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+ if (s == null) {
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2018-03-30 19:00:01 +02:00
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+ return;
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+ }
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+
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2018-07-13 09:43:56 +02:00
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+ if (!s.equals("MC|PingHost")) {
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2018-03-30 19:00:01 +02:00
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+ removeHandler(ctx);
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+ return;
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+ }
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+
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2018-07-13 09:43:56 +02:00
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+ if (!buf.isReadable(Short.BYTES) || !buf.isReadable(buf.readShort())) {
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2018-03-30 19:00:01 +02:00
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+ return;
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+ }
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+
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+ MinecraftServer server = this.b.d();
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+ int protocolVersion = buf.readByte();
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2018-07-13 09:43:56 +02:00
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+ String host = readLegacyString(buf);
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+ if (host == null) {
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+ removeHandler(ctx);
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+ return;
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+ }
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2018-03-30 19:00:01 +02:00
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+ int port = buf.readInt();
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+
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+ if (buf.isReadable()) {
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+ removeHandler(ctx);
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+ return;
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+ }
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+
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+ buf.release();
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+ this.buf = null;
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+
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2019-05-06 01:24:37 +02:00
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+ LOGGER.debug("Ping: (1.6) from {}", ctx.channel().remoteAddress());
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2018-03-30 19:00:01 +02:00
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+
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+ String response = String.format("\u00a71\u0000%d\u0000%s\u0000%s\u0000%d\u0000%d",
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+ Byte.MAX_VALUE, server.getVersion(), server.getMotd(), server.getPlayerCount(), server.getMaxPlayers());
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+ this.a(ctx, this.a(response));
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+ }
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+
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+ private void removeHandler(ChannelHandlerContext ctx) {
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+ ByteBuf buf = this.buf;
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+ this.buf = null;
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+
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+ buf.resetReaderIndex();
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2018-07-13 09:43:56 +02:00
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+ ctx.pipeline().remove(this);
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2018-03-30 19:00:01 +02:00
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+ ctx.fireChannelRead(buf);
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+ }
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2018-07-13 09:43:56 +02:00
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+
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+ @Override
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+ public void handlerRemoved(ChannelHandlerContext ctx) {
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+ if (this.buf != null) {
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+ this.buf.release();
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+ this.buf = null;
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+ }
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+ }
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2018-03-30 19:00:01 +02:00
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+ // Paper end
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+
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private void a(ChannelHandlerContext channelhandlercontext, ByteBuf bytebuf) {
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channelhandlercontext.pipeline().firstContext().writeAndFlush(bytebuf).addListener(ChannelFutureListener.CLOSE);
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}
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