// Simple HTTP server that responds 200 with a test message including client IP. // // Behavior: // - GET returns HTTP/1.1 200 with a message including the requester IP // - HEAD returns the same headers as GET but no body // - Displays incoming X-* headers when present // - If User-Agent contains "curl" or "wget" (case-insensitive), the server // responds with Content-Type: text/plain; otherwise Content-Type: text/html. // - --pem specifies a PEM bundle file (cert chain + private key). When provided, // the server listens on both HTTP (--port) and HTTPS (--tls-port). // Without --pem the server listens on plain HTTP only. // - --look controls which HTML variant is returned for non-CLI agents: // - basic - plain HTML with no external references // - nice - includes Google Font "Noto Sans" (default) // - bootstrap - Bootstrap 5 layout // - tailwind - Tailwind CSS via @tailwindcss/browser@latest // - The URL query parameter "look" (e.g. /?look=nice) overrides --look for // that request only. Values are case-insensitive and must be basic,nice,bootstrap,tailwind. // // Usage: // // go run ok-server.go # binds 0.0.0.0:8080, nice look // go run ok-server.go --look basic // go run ok-server.go -b 127.0.0.1 -p 8080 --look tailwind // go run ok-server.go --pem /path/to/bundle.pem # HTTP :8080 + HTTPS :8443 // go run ok-server.go --pem /path/to/bundle.pem --tls-port 9443 package main import ( "context" "crypto/tls" "flag" "fmt" "html" "net" "net/http" "os" "os/signal" "sort" "strconv" "strings" "syscall" "time" ) const plainTemplate = "Hello, This is a test HTTP server.\n\nYour request came from {ip}.\n\n{proxy_headers_block}Have a nice day!\n" const htmlBasic = ` Test HTTP server

Hello,

This is a test HTTP server.

Your request came from {ip_html}.

{proxy_headers_html}

Have a nice day!

` const htmlNice = ` Test HTTP server

Hello,

This is a test HTTP server.

Your request came from {ip_html}.

{proxy_headers_html}

Have a nice day!

` const htmlBootstrap = ` Test HTTP server

Hello,

This is a test HTTP server.

Your request came from {ip_html}.

{proxy_headers_html}

Have a nice day!

` const htmlTailwind = ` Test HTTP server

Test HTTP server

Simple status page for firewall/testing

Hello,

This is a test HTTP server.

Your request came from {ip_html}.

{proxy_headers_html}

Have a nice day!

` var lookTemplates = map[string]string{ "basic": htmlBasic, "nice": htmlNice, "bootstrap": htmlBootstrap, "tailwind": htmlTailwind, } func getClientIP(r *http.Request) string { host, _, err := net.SplitHostPort(r.RemoteAddr) if err != nil { return r.RemoteAddr } return host } func isCliAgent(ua string) bool { ua = strings.ToLower(ua) return strings.Contains(ua, "curl") || strings.Contains(ua, "wget") } func getRequestLook(r *http.Request) string { look := strings.ToLower(strings.TrimSpace(r.URL.Query().Get("look"))) if _, ok := lookTemplates[look]; ok { return look } return "" } func collectXHeaders(r *http.Request) [][2]string { var result [][2]string for name, values := range r.Header { if strings.HasPrefix(strings.ToLower(name), "x-") { result = append(result, [2]string{name, strings.Join(values, ", ")}) } } sort.Slice(result, func(i, j int) bool { return strings.ToLower(result[i][0]) < strings.ToLower(result[j][0]) }) return result } func proxyMarkup(xHeaders [][2]string) (string, string) { if len(xHeaders) == 0 { return "", "" } lines := make([]string, len(xHeaders)) for i, h := range xHeaders { lines[i] = fmt.Sprintf(" - %s: %s", h[0], h[1]) } block := "Reverse proxy condition: detected via X-* headers.\nX-* headers:\n" + strings.Join(lines, "\n") + "\n\n" htmlItems := make([]string, len(xHeaders)) for i, h := range xHeaders { htmlItems[i] = fmt.Sprintf("
  • %s: %s
    • ", html.EscapeString(h[0]), html.EscapeString(h[1])) } htmlStr := "

    Reverse proxy condition: detected via X-* headers.

    " + "

    X-* headers:

    " return block, htmlStr } func makeBodyAndType(r *http.Request, clientIP, defaultLook string) ([]byte, string) { ua := r.Header.Get("User-Agent") xHeaders := collectXHeaders(r) proxyHeadersBlock, proxyHeadersHTML := proxyMarkup(xHeaders) var ipText, ipHTML string xff := strings.TrimSpace(strings.SplitN(r.Header.Get("X-Forwarded-For"), ",", 2)[0]) if xff != "" { realIP := xff if strings.HasPrefix(realIP, "[") { if idx := strings.Index(realIP, "]"); idx != -1 { realIP = realIP[1:idx] } else { realIP = realIP[1:] } } else if strings.Count(realIP, ":") == 1 { realIP = strings.SplitN(realIP, ":", 2)[0] } ipText = fmt.Sprintf("%s (forwarded by proxy %s)", realIP, clientIP) ipHTML = fmt.Sprintf("%s (forwarded by proxy %s)", html.EscapeString(realIP), html.EscapeString(clientIP)) } else { ipText = clientIP ipHTML = fmt.Sprintf("%s", html.EscapeString(clientIP)) } if isCliAgent(ua) { body := strings.NewReplacer( "{ip}", ipText, "{proxy_headers_block}", proxyHeadersBlock, ).Replace(plainTemplate) return []byte(body), "text/plain; charset=utf-8" } look := getRequestLook(r) if look == "" { look = defaultLook } body := strings.NewReplacer( "{ip_html}", ipHTML, "{proxy_headers_html}", proxyHeadersHTML, ).Replace(lookTemplates[look]) return []byte(body), "text/html; charset=utf-8" } func makeHandler(defaultLook string) http.Handler { return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { clientIP := getClientIP(r) now := time.Now().UTC().Format("02/Jan/2006:15:04:05 +0000") fmt.Fprintf(os.Stderr, "%s - - [%s] \"%s %s\"\n", clientIP, now, r.Method, r.URL.RequestURI()) if r.Method != http.MethodGet && r.Method != http.MethodHead { w.Header().Set("Content-Length", "0") w.WriteHeader(http.StatusMethodNotAllowed) return } body, contentType := makeBodyAndType(r, clientIP, defaultLook) w.Header().Set("Content-Type", contentType) w.Header().Set("Content-Length", strconv.Itoa(len(body))) w.WriteHeader(http.StatusOK) if r.Method != http.MethodHead { w.Write(body) //nolint:errcheck } }) } func main() { fs := flag.NewFlagSet("ok-server", flag.ContinueOnError) fs.Usage = func() { fmt.Println("Usage:") fmt.Println(" go run ok-server.go [-b|--bind ADDRESS] [-p|--port PORT] [--tls-port PORT] [--pem PEMFILE] [--look basic|nice|bootstrap|tailwind]") fmt.Println() fmt.Println("Defaults:") fmt.Println(" --bind 0.0.0.0") fmt.Println(" --port 8080") fmt.Println(" --tls-port 8443") fmt.Println(" --pem (none, plain HTTP only)") fmt.Println(" --look nice") } var bind, look, pemFile string var port, tlsPort int fs.StringVar(&bind, "b", "0.0.0.0", "address to bind to") fs.StringVar(&bind, "bind", "0.0.0.0", "address to bind to") fs.IntVar(&port, "p", 8080, "HTTP port") fs.IntVar(&port, "port", 8080, "HTTP port") fs.IntVar(&tlsPort, "tls-port", 8443, "HTTPS port (when --pem is provided)") fs.StringVar(&pemFile, "pem", "", "PEM bundle (cert+key); enables HTTPS alongside HTTP") fs.StringVar(&look, "look", "nice", "default HTML look: basic|nice|bootstrap|tailwind") if err := fs.Parse(os.Args[1:]); err != nil { if err == flag.ErrHelp { os.Exit(0) } fmt.Fprintln(os.Stderr, err) os.Exit(2) } if _, ok := lookTemplates[look]; !ok { fmt.Fprintf(os.Stderr, "Invalid look: %q (expected one of: basic, nice, bootstrap, tailwind)\n", look) os.Exit(2) } handler := makeHandler(look) httpSrv := &http.Server{ Addr: fmt.Sprintf("%s:%d", bind, port), Handler: handler, } var httpsSrv *http.Server if pemFile != "" { cert, err := tls.LoadX509KeyPair(pemFile, pemFile) if err != nil { fmt.Fprintf(os.Stderr, "Cannot load PEM file %q: %v\n", pemFile, err) os.Exit(1) } httpsSrv = &http.Server{ Addr: fmt.Sprintf("%s:%d", bind, tlsPort), Handler: handler, TLSConfig: &tls.Config{ Certificates: []tls.Certificate{cert}, }, } } go func() { if err := httpSrv.ListenAndServe(); err != nil && err != http.ErrServerClosed { fmt.Fprintf(os.Stderr, "HTTP server error: %v\n", err) os.Exit(1) } }() fmt.Printf("Serving on http://%s:%d (default look=%s)\n", bind, port, look) if httpsSrv != nil { go func() { if err := httpsSrv.ListenAndServeTLS("", ""); err != nil && err != http.ErrServerClosed { fmt.Fprintf(os.Stderr, "HTTPS server error: %v\n", err) os.Exit(1) } }() fmt.Printf("Serving on https://%s:%d (default look=%s)\n", bind, tlsPort, look) } quit := make(chan os.Signal, 1) signal.Notify(quit, syscall.SIGINT, syscall.SIGTERM) <-quit fmt.Println("\nShutting down server") ctx := context.Background() httpSrv.Shutdown(ctx) if httpsSrv != nil { httpsSrv.Shutdown(ctx) } }