hello.go

package main

import (
	"crypto/tls"
	"flag"
	"fmt"
	"log"
	"log/slog"
	"net/http"
)

var (
	addr     = flag.String("addr", ":8080", "addr:port")
	certFile = flag.String("cert", "", "TLS certFile")
	keyFile  = flag.String("key", "", "TLS keyFile")
)

func main() {
	flag.Parse()
	log.SetFlags(0)

	enableTLS := *certFile != "" || *keyFile != ""

	if enableTLS {
		if *certFile == "" {
			log.Fatal("no certFile")
		}
		if *keyFile == "" {
			log.Fatal("no keyFile")
		}
	}

	http.HandleFunc("/", func(w http.ResponseWriter, req *http.Request) {
		var (
			cipherSuite        = ""
			negotiatedProtocol = ""
			tlsVersion         = ""
		)
		if req.TLS != nil {
			cipherSuite = tls.CipherSuiteName(req.TLS.CipherSuite)
			negotiatedProtocol = req.TLS.NegotiatedProtocol
			tlsVersion = tls.VersionName(req.TLS.Version)
		}
		slog.InfoContext(req.Context(), "request",
			"proto", req.Proto,
			"method", req.Method,
			"host", req.Host,
			"url", req.URL.String(),
			"pattern", req.Pattern,
			"remoteAddr", req.RemoteAddr,
			"userAgent", req.UserAgent(),
			slog.Group("tls",
				"cipherSuite", cipherSuite,
				"negotiatedProtocol", negotiatedProtocol,
				"version", tlsVersion,
			),
		)
		fmt.Fprintf(w, "hello, %s\n", req.RemoteAddr)
	})

	var err error
	if enableTLS {
		err = http.ListenAndServeTLS(*addr, *certFile, *keyFile, nil)
	} else {
		err = http.ListenAndServe(*addr, nil)
	}
	if err != nil {
		log.Fatal(err)
	}
}