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一、背景与原理

1.1 问题场景

在TCP四层代理场景下，Nginx作为反向代理将客户端请求转发至Netty实现的RPC服务。由于经过代理转发，RPC服务默认只能获取到Nginx服务器的IP地址。需要通过Proxy Protocol协议传递客户端真实IP。

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网络架构影响分析

1.1 客户端与Nginx之间存在的NAT/VPN

场景	可获取IP类型	技术原理
企业级NAT网关	仅NAT出口公网IP	NAT设备替换源IP地址
家用路由器NAT	路由器WAN口IP	私有地址转换为公网IP
全局VPN接入	VPN服务器出口IP	流量封装后隧道传输

结论：Proxy Protocol只能传递Nginx直接看到的IP（即NAT/VPN出口地址）

1.2 Nginx与RPC服务之间的NAT

场景	影响程度	解决方案
普通NAT转发	无影响	保持现有Proxy Protocol配置
复杂SDN网络	需验证	确保TCP连接透传代理协议头

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1.2 技术原理

• Proxy Protocol：由HAProxy提出的传输层协议扩展，在建立TCP连接时发送包含源地址信息的头部
• Nginx配置：proxy_protocol on指令启用协议支持
• Netty解码：通过HAProxyMessageDecoder解析协议头

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二、环境配置验证

2.1 Nginx配置

仅用于演示，仅展示核心配置。

# 定义后端服务器组
upstream rpc_backend {server 10.0.0.1:12345;server 10.0.0.2:12345;
}# 配置TCP代理
stream {server {listen 12345;proxy_pass rpc_backend;proxy_protocol on;}
}

在Nginx的stream模块中，设置一个TCP代理服务器，监听12345端口，将所有到达该端口的连接通过proxy protocol转发到rpc_backend定的后端服务器组。这样后端服务器可以获取到原始客户端的IP地址等信息，前提是后端服务支持proxy protocol。

proxy_protocol on

• 启用PROXY协议（版本1或2），在转发流量时，将客户端的原始信息（如源IP、端口）附加到数据包头部。
• 作用：使后端服务器能获取客户端真实IP，而非Nginx代理的IP。
• 要求：后端服务必须支持并配置解析PROXY协议。

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2.2 版本要求

• Nginx ≥ 1.9.0 我这里是1.27.1
• Netty ≥ 4.1.x 我这里是 4.1.109

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三、Netty服务端实现

3.1 Pipeline配置（核心代码）

public class RpcServerInitializer extends ChannelInitializer<SocketChannel> {@Overrideprotected void initChannel(SocketChannel ch) {ChannelPipeline pipeline = ch.pipeline();// 添加PROXY协议解码器pipeline.addLast(new HAProxyMessageDecoder());// 自定义协议处理器pipeline.addLast(new ProxyProtocolHandler());pipeline.addLast(new RpcMessageDecoder());pipeline.addLast(new RpcMessageHandler());}
}

3.2 协议处理器实现

提取IP

public class ProxyProtocolHandler extends ChannelInboundHandlerAdapter {@Overridepublic void channelRead(ChannelHandlerContext ctx, Object msg) {if (msg instanceof HAProxyMessage) {HAProxyMessage proxyMessage = (HAProxyMessage) msg;// 提取真实客户端地址String clientIp = proxyMessage.sourceAddress();int clientPort = proxyMessage.sourcePort();// 存储到Channel属性中ctx.channel().attr(CLIENT_IP_ATTRIBUTE).set(clientIp);// 释放资源并移除当前消息ReferenceCountUtil.release(msg);return;}// 非PROXY协议消息继续传递ctx.fireChannelRead(msg);}@Overridepublic void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {log.error("Proxy protocol parsing failed", cause);ctx.close();}
}

3.3 业务处理器调用示例

使用IP

public class RpcMessageHandler extends SimpleChannelInboundHandler<RpcRequest> {@Overrideprotected void channelRead0(ChannelHandlerContext ctx, RpcRequest request) {String clientIp = ctx.channel().attr(CLIENT_IP_ATTRIBUTE).get();log.info("Received request from {}: {}", clientIp, request);// 业务处理逻辑...}
}

四、关键实现细节

4.1 解码顺序保障

• HAProxyMessageDecoder必须作为第一个入站处理器
• 需要处理完PROXY协议头后立即移除解码器（自动完成）

我抓了个包，如下

右键 Proxyv1 追踪流

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4.2 地址类型处理

// 支持IPv4/IPv6地址类型判断
if (proxyMessage.proxyProtocol().addressType() == HAProxyAddressType.IPV4) {// IPv4处理逻辑
} else if (proxyMessage.proxyProtocol().addressType() == HAProxyAddressType.IPV6) {// IPv6处理逻辑
}

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4.3 安全性增强

// 限制允许的代理服务器IP（可选）
List<String> allowedProxies = Arrays.asList("10.0.0.0/8", "192.168.0.0/16");
if (!isAllowedProxy(proxyMessage.destinationAddress())) {ctx.close();return;
}

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五、异常处理方案

异常场景	处理方案
无效PROXY头	记录日志并关闭连接
协议版本不匹配	返回错误响应码
地址格式错误	使用默认地址并告警

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六、 HAProxyMessageDecoder

/** Copyright 2014 The Netty Project** The Netty Project licenses this file to you under the Apache License,* version 2.0 (the "License"); you may not use this file except in compliance* with the License. You may obtain a copy of the License at:**   https://www.apache.org/licenses/LICENSE-2.0** Unless required by applicable law or agreed to in writing, software* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the* License for the specific language governing permissions and limitations* under the License.*/
package io.netty.handler.codec.haproxy;import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.ByteToMessageDecoder;
import io.netty.handler.codec.ProtocolDetectionResult;
import io.netty.util.CharsetUtil;import java.util.List;import static io.netty.handler.codec.haproxy.HAProxyConstants.*;/*** Decodes an HAProxy proxy protocol header** @see <a href="https://haproxy.1wt.eu/download/1.5/doc/proxy-protocol.txt">Proxy Protocol Specification</a>*/
public class HAProxyMessageDecoder extends ByteToMessageDecoder {/*** Maximum possible length of a v1 proxy protocol header per spec*/private static final int V1_MAX_LENGTH = 108;/*** Maximum possible length of a v2 proxy protocol header (fixed 16 bytes + max unsigned short)*/private static final int V2_MAX_LENGTH = 16 + 65535;/*** Minimum possible length of a fully functioning v2 proxy protocol header (fixed 16 bytes + v2 address info space)*/private static final int V2_MIN_LENGTH = 16 + 216;/*** Maximum possible length for v2 additional TLV data (max unsigned short - max v2 address info space)*/private static final int V2_MAX_TLV = 65535 - 216;/*** Binary header prefix length*/private static final int BINARY_PREFIX_LENGTH = BINARY_PREFIX.length;/*** {@link ProtocolDetectionResult} for {@link HAProxyProtocolVersion#V1}.*/private static final ProtocolDetectionResult<HAProxyProtocolVersion> DETECTION_RESULT_V1 =ProtocolDetectionResult.detected(HAProxyProtocolVersion.V1);/*** {@link ProtocolDetectionResult} for {@link HAProxyProtocolVersion#V2}.*/private static final ProtocolDetectionResult<HAProxyProtocolVersion> DETECTION_RESULT_V2 =ProtocolDetectionResult.detected(HAProxyProtocolVersion.V2);/*** Used to extract a header frame out of the {@link ByteBuf} and return it.*/private HeaderExtractor headerExtractor;/*** {@code true} if we're discarding input because we're already over maxLength*/private boolean discarding;/*** Number of discarded bytes*/private int discardedBytes;/*** Whether or not to throw an exception as soon as we exceed maxLength.*/private final boolean failFast;/*** {@code true} if we're finished decoding the proxy protocol header*/private boolean finished;/*** Protocol specification version*/private int version = -1;/*** The latest v2 spec (2014/05/18) allows for additional data to be sent in the proxy protocol header beyond the* address information block so now we need a configurable max header size*/private final int v2MaxHeaderSize;/*** Creates a new decoder with no additional data (TLV) restrictions, and should throw an exception as soon as* we exceed maxLength.*/public HAProxyMessageDecoder() {this(true);}/*** Creates a new decoder with no additional data (TLV) restrictions, whether or not to throw an exception as soon* as we exceed maxLength.** @param failFast Whether or not to throw an exception as soon as we exceed maxLength*/public HAProxyMessageDecoder(boolean failFast) {v2MaxHeaderSize = V2_MAX_LENGTH;this.failFast = failFast;}/*** Creates a new decoder with restricted additional data (TLV) size, and should throw an exception as soon as* we exceed maxLength.* <p>* <b>Note:</b> limiting TLV size only affects processing of v2, binary headers. Also, as allowed by the 1.5 spec* TLV data is currently ignored. For maximum performance it would be best to configure your upstream proxy host to* <b>NOT</b> send TLV data and instantiate with a max TLV size of {@code 0}.* </p>** @param maxTlvSize maximum number of bytes allowed for additional data (Type-Length-Value vectors) in a v2 header*/public HAProxyMessageDecoder(int maxTlvSize) {this(maxTlvSize, true);}/*** Creates a new decoder with restricted additional data (TLV) size, whether or not to throw an exception as soon* as we exceed maxLength.** @param maxTlvSize maximum number of bytes allowed for additional data (Type-Length-Value vectors) in a v2 header* @param failFast Whether or not to throw an exception as soon as we exceed maxLength*/public HAProxyMessageDecoder(int maxTlvSize, boolean failFast) {if (maxTlvSize < 1) {v2MaxHeaderSize = V2_MIN_LENGTH;} else if (maxTlvSize > V2_MAX_TLV) {v2MaxHeaderSize = V2_MAX_LENGTH;} else {int calcMax = maxTlvSize + V2_MIN_LENGTH;if (calcMax > V2_MAX_LENGTH) {  // lgtm[java/constant-comparison]v2MaxHeaderSize = V2_MAX_LENGTH;} else {v2MaxHeaderSize = calcMax;}}this.failFast = failFast;}/*** Returns the proxy protocol specification version in the buffer if the version is found.* Returns -1 if no version was found in the buffer.*/private static int findVersion(final ByteBuf buffer) {final int n = buffer.readableBytes();// per spec, the version number is found in the 13th byteif (n < 13) {return -1;}int idx = buffer.readerIndex();// 主要修改这里if (match(TEXT_PREFIX, buffer, idx)) {return 1;}if (match(BINARY_PREFIX, buffer, idx)) {return buffer.getByte(idx + BINARY_PREFIX_LENGTH);}return -1;
//        return match(BINARY_PREFIX, buffer, idx) ? buffer.getByte(idx + BINARY_PREFIX_LENGTH) : 1;}/*** Returns the index in the buffer of the end of header if found.* Returns -1 if no end of header was found in the buffer.*/private static int findEndOfHeader(final ByteBuf buffer) {final int n = buffer.readableBytes();// per spec, the 15th and 16th bytes contain the address length in bytesif (n < 16) {return -1;}int offset = buffer.readerIndex() + 14;// the total header length will be a fixed 16 byte sequence + the dynamic address information blockint totalHeaderBytes = 16 + buffer.getUnsignedShort(offset);// ensure we actually have the full header availableif (n >= totalHeaderBytes) {return totalHeaderBytes;} else {return -1;}}/*** Returns the index in the buffer of the end of line found.* Returns -1 if no end of line was found in the buffer.*/private static int findEndOfLine(final ByteBuf buffer) {final int n = buffer.writerIndex();for (int i = buffer.readerIndex(); i < n; i++) {final byte b = buffer.getByte(i);if (b == '\r' && i < n - 1 && buffer.getByte(i + 1) == '\n') {return i;  // \r\n}}return -1;  // Not found.}@Overridepublic boolean isSingleDecode() {// ByteToMessageDecoder uses this method to optionally break out of the decoding loop after each unit of work.// Since we only ever want to decode a single header we always return true to save a bit of work here.return true;}@Overridepublic void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {super.channelRead(ctx, msg);if (finished) {ctx.pipeline().remove(this);}}@Overrideprotected final void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {// determine the specification versionif (version == -1) {if ((version = findVersion(in)) == -1) {// 头部finished = true;return;}}ByteBuf decoded;if (version == 1) {decoded = decodeLine(ctx, in);} else {decoded = decodeStruct(ctx, in);}if (decoded != null) {finished = true;try {if (version == 1) {out.add(HAProxyMessage.decodeHeader(decoded.toString(CharsetUtil.US_ASCII)));} else {out.add(HAProxyMessage.decodeHeader(decoded));}} catch (HAProxyProtocolException e) {fail(ctx, null, e);}}}/*** Create a frame out of the {@link ByteBuf} and return it.** @param ctx     the {@link ChannelHandlerContext} which this {@link HAProxyMessageDecoder} belongs to* @param buffer  the {@link ByteBuf} from which to read data* @return frame  the {@link ByteBuf} which represent the frame or {@code null} if no frame could*                be created*/private ByteBuf decodeStruct(ChannelHandlerContext ctx, ByteBuf buffer) throws Exception {if (headerExtractor == null) {headerExtractor = new StructHeaderExtractor(v2MaxHeaderSize);}return headerExtractor.extract(ctx, buffer);}/*** Create a frame out of the {@link ByteBuf} and return it.** @param ctx     the {@link ChannelHandlerContext} which this {@link HAProxyMessageDecoder} belongs to* @param buffer  the {@link ByteBuf} from which to read data* @return frame  the {@link ByteBuf} which represent the frame or {@code null} if no frame could*                be created*/private ByteBuf decodeLine(ChannelHandlerContext ctx, ByteBuf buffer) throws Exception {if (headerExtractor == null) {headerExtractor = new LineHeaderExtractor(V1_MAX_LENGTH);}return headerExtractor.extract(ctx, buffer);}private void failOverLimit(final ChannelHandlerContext ctx, int length) {failOverLimit(ctx, String.valueOf(length));}private void failOverLimit(final ChannelHandlerContext ctx, String length) {int maxLength = version == 1 ? V1_MAX_LENGTH : v2MaxHeaderSize;fail(ctx, "header length (" + length + ") exceeds the allowed maximum (" + maxLength + ')', null);}private void fail(final ChannelHandlerContext ctx, String errMsg, Exception e) {finished = true;ctx.close(); // drop connection immediately per specHAProxyProtocolException ppex;if (errMsg != null && e != null) {ppex = new HAProxyProtocolException(errMsg, e);} else if (errMsg != null) {ppex = new HAProxyProtocolException(errMsg);} else if (e != null) {ppex = new HAProxyProtocolException(e);} else {ppex = new HAProxyProtocolException();}throw ppex;}/*** Returns the {@link ProtocolDetectionResult} for the given {@link ByteBuf}.*/public static ProtocolDetectionResult<HAProxyProtocolVersion> detectProtocol(ByteBuf buffer) {if (buffer.readableBytes() < 12) {return ProtocolDetectionResult.needsMoreData();}int idx = buffer.readerIndex();if (match(BINARY_PREFIX, buffer, idx)) {return DETECTION_RESULT_V2;}if (match(TEXT_PREFIX, buffer, idx)) {return DETECTION_RESULT_V1;}return ProtocolDetectionResult.invalid();}private static boolean match(byte[] prefix, ByteBuf buffer, int idx) {for (int i = 0; i < prefix.length; i++) {final byte b = buffer.getByte(idx + i);if (b != prefix[i]) {return false;}}return true;}/*** HeaderExtractor create a header frame out of the {@link ByteBuf}.*/private abstract class HeaderExtractor {/** Header max size */private final int maxHeaderSize;protected HeaderExtractor(int maxHeaderSize) {this.maxHeaderSize = maxHeaderSize;}/*** Create a frame out of the {@link ByteBuf} and return it.** @param ctx     the {@link ChannelHandlerContext} which this {@link HAProxyMessageDecoder} belongs to* @param buffer  the {@link ByteBuf} from which to read data* @return frame  the {@link ByteBuf} which represent the frame or {@code null} if no frame could*                be created* @throws Exception if exceed maxLength*/public ByteBuf extract(ChannelHandlerContext ctx, ByteBuf buffer) throws Exception {final int eoh = findEndOfHeader(buffer);if (!discarding) {if (eoh >= 0) {final int length = eoh - buffer.readerIndex();if (length > maxHeaderSize) {buffer.readerIndex(eoh + delimiterLength(buffer, eoh));failOverLimit(ctx, length);return null;}ByteBuf frame = buffer.readSlice(length);buffer.skipBytes(delimiterLength(buffer, eoh));return frame;} else {final int length = buffer.readableBytes();if (length > maxHeaderSize) {discardedBytes = length;buffer.skipBytes(length);discarding = true;if (failFast) {failOverLimit(ctx, "over " + discardedBytes);}}return null;}} else {if (eoh >= 0) {final int length = discardedBytes + eoh - buffer.readerIndex();buffer.readerIndex(eoh + delimiterLength(buffer, eoh));discardedBytes = 0;discarding = false;if (!failFast) {failOverLimit(ctx, "over " + length);}} else {discardedBytes += buffer.readableBytes();buffer.skipBytes(buffer.readableBytes());}return null;}}/*** Find the end of the header from the given {@link ByteBuf}，the end may be a CRLF, or the length given by the* header.** @param buffer the buffer to be searched* @return {@code -1} if can not find the end, otherwise return the buffer index of end*/protected abstract int findEndOfHeader(ByteBuf buffer);/*** Get the length of the header delimiter.** @param buffer the buffer where delimiter is located* @param eoh index of delimiter* @return length of the delimiter*/protected abstract int delimiterLength(ByteBuf buffer, int eoh);}private final class LineHeaderExtractor extends HeaderExtractor {LineHeaderExtractor(int maxHeaderSize) {super(maxHeaderSize);}@Overrideprotected int findEndOfHeader(ByteBuf buffer) {return findEndOfLine(buffer);}@Overrideprotected int delimiterLength(ByteBuf buffer, int eoh) {return buffer.getByte(eoh) == '\r' ? 2 : 1;}}private final class StructHeaderExtractor extends HeaderExtractor {StructHeaderExtractor(int maxHeaderSize) {super(maxHeaderSize);}@Overrideprotected int findEndOfHeader(ByteBuf buffer) {return HAProxyMessageDecoder.findEndOfHeader(buffer);}@Overrideprotected int delimiterLength(ByteBuf buffer, int eoh) {return 0;}}
}

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七、总结

在存在NAT或VPN的网络架构中，通过Proxy Protocol获取客户端真实IP的能力受限于网络设备的位置。

若NAT/VPN位于客户端与Nginx之间（如企业VPN或家庭路由），Proxy Protocol仅能传递经过NAT转换或VPN隧道出口的IP（如公网IP或VPN分配地址），无法穿透获取终端设备的内网真实IP。若需突破此限制，可采取混合方案：客户端主动上报IP（需改造客户端代码）并配合网络设备改造（如VPN网关记录原始IP、专用隧道协议）。但需注意隐私合规风险，避免采集敏感信息。

对于常规业务场景，Proxy Protocol结合Nginx配置已能满足“获取客户端侧网络出口IP”的需求，但若涉及终端设备溯源，需结合应用层协议与网络基础设施深度协同实现。