api: add explicit readiness check

Now the readiness is governed by a function func() bool.

api.go

@@ -17,24 +17,20 @@ import (
 	"github.com/saucelabs/forwarder/internal/version"
 )
 
-type server interface {
-	Addr() string
-}
-
 // APIHandler serves API endpoints.
 // It provides health and readiness endpoints prometheus metrics, and pprof debug endpoints.
 type APIHandler struct {
 	mux    *http.ServeMux
-	server server
+	ready  func() bool
 	config string
 	script string
 }
 
-func NewAPIHandler(r prometheus.Gatherer, s server, config, pac string) *APIHandler {
+func NewAPIHandler(r prometheus.Gatherer, ready func() bool, config, pac string) *APIHandler {
 	m := http.NewServeMux()
 	a := &APIHandler{
 		mux:    m,
-		server: s,
+		ready:  ready,
 		config: config,
 		script: pac,
 	}
@@ -60,7 +56,7 @@ func (h *APIHandler) healthz(w http.ResponseWriter, r *http.Request) {
 }
 
 func (h *APIHandler) readyz(w http.ResponseWriter, r *http.Request) {
-	if h.server.Addr() != "" {
+	if h.ready() {
 		w.WriteHeader(http.StatusOK)
 		w.Header().Set("Content-Type", "text/plain")
 		w.Write([]byte("OK"))

cmd/forwarder/httpbin/httpbin.go

@@ -32,7 +32,7 @@ func (c *command) RunE(cmd *cobra.Command, args []string) error {
 	}
 
 	r := prometheus.NewRegistry()
-	a, err := forwarder.NewHTTPServer(c.apiServerConfig, forwarder.NewAPIHandler(r, s, config, ""), logger.Named("api"))
+	a, err := forwarder.NewHTTPServer(c.apiServerConfig, forwarder.NewAPIHandler(r, s.Ready, config, ""), logger.Named("api"))
 	if err != nil {
 		return err
 	}

cmd/forwarder/proxy/proxy.go

@@ -104,7 +104,7 @@ func (c *command) RunE(cmd *cobra.Command, args []string) error {
 	f = append(f, p.Run)
 
 	if c.apiServerConfig.Addr != "" {
-		h := forwarder.NewAPIHandler(c.promReg, p, config, script)
+		h := forwarder.NewAPIHandler(c.promReg, p.Ready, config, script)
 		a, err := forwarder.NewHTTPServer(c.apiServerConfig, h, logger.Named("api"))
 		if err != nil {
 			return err

http_proxy.go

@@ -437,6 +437,11 @@ func (hp *HTTPProxy) Addr() string {
 	return *addr
 }
 
+// Ready returns true if the server is running and ready to accept requests.
+func (hp *HTTPProxy) Ready() bool {
+	return hp.Addr() != ""
+}
+
 // headerRemover removes headers that match given prefix.
 type headerRemover struct {
 	prefix string

http_server.go

@@ -274,3 +274,8 @@ func (hs *HTTPServer) Addr() string {
 	}
 	return *addr
 }
+
+// Ready returns true if the server is running and ready to accept requests.
+func (hs *HTTPServer) Ready() bool {
+	return hs.Addr() != ""
+}