Proxy Protocol Support in Curl

Reading time: 1min.

I’ve came across the following tweet the other day, and I couldn’t be more excited:

This is exciting to me as the work I’ve been doing in viaproxy had one caveat: testing it works was a bit convoluted, as I was doing by running an HAProxy instance with a custom configuration like the following:

    maxconn 4000
    log local0

    timeout connect 10s
    timeout client  1m
    timeout server  1m

listen without-send-proxy
    mode tcp
    log global
    option tcplog
    bind *:17654
    server app1

listen with-send-proxy
    mode tcp
    log global
    option tcplog
    bind *:27654
    bind ipv6@:27654
    server app1 send-proxy

Luckily commit 6baeb6df35d24740c55239f24b5fc4ce86f375a5 adds a new --haproxy-protocol that, as documented, will do the following:

Send a HAProxy PROXY protocol header at the beginning of the connection. This is used by some load balancers and reverse proxies to indicate the client’s true IP address and port.

This option is primarily useful when sending test requests to a service that expects this header.

Reading the commit changes is very enlightening, too, as it is a great example of nice and simple C code. I’m looking forward to the release!