Suggestion: Dynamic Proxy Protocol Listener

[134130]

• There can be requirements that server can listen and serve whenever proxy protocol is set or not for identifying real client's ip.
• I will make PR if many people needs it.

[Cosin]

It's a very useful feature. I'm waiting for your PR :)

[pires]

It's a very useful feature. I'm waiting for your PR :)

Same!

[dgl]

Implementing such a thing would like open a security hole, see the spec: https://www.haproxy.org/download/3.1/doc/proxy-protocol.txt

5. Security considerations

[...]

Implementers should be very careful about not trying to automatically detect
whether they have to decode the header or not, but rather they must only rely
on a configuration parameter. Indeed, if the opportunity is left to a normal
client to use the protocol, it will be able to hide its activities or make them
appear as coming from somewhere else. However, accepting the header only from a
number of known sources should be safe.

[134130]

Yes, but it depends on the user's choice.

Restricting on the library level makes sense, but if the feature is useful for testing, it makes sense to support it, too. There are some cases like InsecureSkipTLSVerify for curl.

But the feature is not willing by folks, so there is no need to implement it immediately.