ALPN support for network tests 🔗 link

Hello,

I had a need to monitor some services that are being multiplexed/proxied by Nginx with the stream module like so:

stream {
         map $ssl_preread_alpn_protocols $proxy {
             default 127.0.0.1:8443;
             ~\bsmtp\b 127.0.0.1:465;
             ~\bimap\b 127.0.0.1:993;
         }

         server {
                 listen 443;
                 listen [::]:443;

                 proxy_pass $proxy;
                 ssl_preread on;
         }
}

This detects the ALPN handshake and passes the traffic through to the real IMAP or SMTP backend. Monitoring this was not possible with Xymon, but I have a working implementation attached. This will allow you to define a new protocol like

[imaps443]

     options ssl,alpn=imap

     port 443


Now I can successfully monitor these services. I considered trying to extend the http monitoring tests to allow this as well so you can force HTTP/2 or HTTP/3 even but I don't think that's possible. Perhaps in another life the HTTP testing should be refactored around libcurl so a giant featureset becomes automatically available... :)

Disclaimer: this patch was only made possible with the help of Qwen as I'm not super experienced in C. I didn't bother cleaning up its obnoxious inline comments, but after a cursory review it doesn't seem like bad code...


Mark