Support SOCKS5 proxy for tri protocol in NettyConnectionClient

[ljlao]

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Apache Dubbo Component

Java SDK (apache/dubbo)

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Hello maintainers,

We are currently using Dubbo 3.3.6 with the tri (Triple) protocol. While reviewing the source code, I noticed that org.apache.dubbo.remoting.transport.netty4.NettyConnectionClient still contains the following TODO:

// set null but do not close this client, it will be reconnecting in the future
ch.closeFuture().addListener(channelFuture -> clearNettyChannel());
// TODO support Socks5

From our current testing, it seems that tri protocol does not yet support SOCKS5 proxying on the client side. JVM-level proxy settings such as:

-DsocksProxyHost=...
-DsocksProxyPort=...

do not appear to work for tri connections, which is understandable since the client is based on Netty rather than plain JDK sockets.

We have a real use case for this feature, such as:

• local development environments accessing remote Dubbo services through a SOCKS5 proxy
• cross-network or restricted-network scenarios where direct connectivity is not available

Could you please clarify:

1. Is SOCKS5 support for tri protocol already on the roadmap?
2. If yes, is there any planned version or milestone for it?
3. If not, what would be the recommended extension point or workaround for now?
   For example, is it expected to support something like Netty's Socks5ProxyHandler in the client pipeline in the future?

Environment:

• Dubbo version: 3.3.6
• Protocol: tri / Triple
• Transport: Netty

Thanks in advance.

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[zrlw]

@ljlao Could you test whether #16285 meets your requirements?