Add a helper command to inspect PROXY connections

The server can be run as follows:

  cd cmd/http-echo
  go run main.go

Then in a separate shell:

  curl http://127.0.0.1/proxy-protocol/used --haproxy-protocol
  false

  curl http://127.0.0.1/proxy-protocol/used --haproxy-protocol
  true

This tool could live outside this repository and may one day just do
that, once it has more fetures and could replace the nginx hello server
used in other places.

Author: href

cmd/http-echo/go.mod

@@ -0,0 +1,5 @@
+module github.com/cloudscale-ch/cloudscale-cloud-controller-manager/cmd/http-echo
+
+go 1.23.0
+
+require github.com/pires/go-proxyproto v0.7.0

cmd/http-echo/go.sum

@@ -0,0 +1,2 @@
+github.com/pires/go-proxyproto v0.7.0 h1:IukmRewDQFWC7kfnb66CSomk2q/seBuilHBYFwyq0Hs=
+github.com/pires/go-proxyproto v0.7.0/go.mod h1:Vz/1JPY/OACxWGQNIRY2BeyDmpoaWmEP40O9LbuiFR4=

cmd/http-echo/main.go

@@ -0,0 +1,73 @@
+// A http echo server to get information about connections made to it.
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"net"
+	"net/http"
+	"time"
+
+	proxyproto "github.com/pires/go-proxyproto"
+)
+
+func main() {
+	host := flag.String("host", "127.0.0.1", "Host to connect to")
+	port := flag.Int("port", 8080, "Port to connect to")
+
+	flag.Parse()
+
+	serve(*host, *port)
+}
+
+// log http requests in basic fashion
+func log(h http.Handler) http.Handler {
+	return http.HandlerFunc(
+		func(w http.ResponseWriter, r *http.Request) {
+			h.ServeHTTP(w, r)
+			fmt.Printf("%s %s (%s)\n", r.Method, r.RequestURI, r.RemoteAddr)
+		})
+}
+
+// serve HTTP API on the given host and port
+func serve(host string, port int) {
+	router := http.NewServeMux()
+
+	// Returns 'true' if the PROXY protocol was used for the given connection
+	router.HandleFunc("GET /proxy-protocol/used",
+		func(w http.ResponseWriter, r *http.Request) {
+			fmt.Fprintln(w, r.Context().Value("HasProxyHeader"))
+		})
+
+	addr := fmt.Sprintf("%s:%d", host, port)
+
+	server := http.Server{
+		Addr:    addr,
+		Handler: log(router),
+		ConnContext: func(ctx context.Context, c net.Conn) context.Context {
+			hasProxyHeader := false
+
+			if c, ok := c.(*proxyproto.Conn); ok {
+				hasProxyHeader = c.ProxyHeader() != nil
+			}
+
+			return context.WithValue(ctx, "HasProxyHeader", hasProxyHeader)
+		},
+	}
+
+	listener, err := net.Listen("tcp", server.Addr)
+	if err != nil {
+		panic(err)
+	}
+
+	fmt.Printf("Listening on %s\n", addr)
+
+	proxyListener := &proxyproto.Listener{
+		Listener:          listener,
+		ReadHeaderTimeout: 10 * time.Second,
+	}
+	defer proxyListener.Close()
+
+	server.Serve(proxyListener)
+}