Add /server-ip endpoint to return server's local IP address

httpbin/handlers.go

@@ -166,6 +166,13 @@ func (h *HTTPBin) Headers(w http.ResponseWriter, r *http.Request) {
 	})
 }
 
+// ServerIP echoes the IP address of the server handling the request
+func (h *HTTPBin) ServerIP(w http.ResponseWriter, _ *http.Request) {
+	writeJSON(http.StatusOK, w, &serverIPResponse{
+		ServerIP: getServerIP(),
+	})
+}
+
 type statusCase struct {
 	headers map[string]string
 	body    []byte

httpbin/helpers.go

@@ -106,6 +106,38 @@ func getURL(r *http.Request) *url.URL {
 	}
 }
 
+// getServerIP attempts to determine the current server's primary IP address
+// (e.g., Pod IP in Kubernetes). It prefers non-loopback IPv4 addresses, then
+// falls back to non-loopback IPv6 if necessary.
+func getServerIP() string {
+	// Prefer non-loopback IPv4 from interface addresses
+	if addrs, err := net.InterfaceAddrs(); err == nil {
+		var v6Fallback string
+		for _, a := range addrs {
+			if ipnet, ok := a.(*net.IPNet); ok && !ipnet.IP.IsLoopback() {
+				ip := ipnet.IP
+				if v4 := ip.To4(); v4 != nil {
+					return v4.String()
+				}
+				if v6Fallback == "" {
+					v6Fallback = ip.String()
+				}
+			}
+		}
+		if v6Fallback != "" {
+			return v6Fallback
+		}
+	}
+	// As a last resort, infer via a UDP dial (no packets actually sent)
+	if conn, err := net.Dial("udp", "8.8.8.8:80"); err == nil {
+		defer conn.Close()
+		if udp, ok := conn.LocalAddr().(*net.UDPAddr); ok && udp.IP != nil {
+			return udp.IP.String()
+		}
+	}
+	return ""
+}
+
 func writeResponse(w http.ResponseWriter, status int, contentType string, body []byte) {
 	w.Header().Set("Content-Type", contentType)
 	w.WriteHeader(status)

httpbin/httpbin.go

@@ -181,6 +181,7 @@ func (h *HTTPBin) Handler() http.Handler {
 	mux.HandleFunc("/image", h.ImageAccept)
 	mux.HandleFunc("/image/{kind}", h.Image)
 	mux.HandleFunc("/ip", h.IP)
+	mux.HandleFunc("/server-ip", h.ServerIP)
 	mux.HandleFunc("/json", h.JSON)
 	mux.HandleFunc("/links/{numLinks}", h.Links)
 	mux.HandleFunc("/links/{numLinks}/{offset}", h.Links)

httpbin/responses.go

@@ -87,6 +87,10 @@ type hostnameResponse struct {
 	Hostname string `json:"hostname"`
 }
 
+type serverIPResponse struct {
+	ServerIP string `json:"server_ip"`
+}
+
 type errorRespnose struct {
 	StatusCode int    `json:"status_code"`
 	Error      string `json:"error"`