Build the HTTP server in a separate function

Reduces cyclomatic complexity score and makes code more readable.

serverutil/http.go

@@ -20,43 +20,63 @@ var gracefulShutdownTimeout = 3 * time.Second
 type ServerConfig struct {
 	TLS                 *TLSServerConfig `yaml:"tls"`
 	MaxInflightRequests int              `yaml:"max_inflight_requests"`
+	TrustedForwarders   []string         `yaml:"trusted_forwarders"`
 }
 
-// Serve HTTP(S) content on the specified address. If serverConfig is
-// not nil, enable HTTPS and TLS authentication.
-//
-// This function will return an error if there are problems creating
-// the listener, otherwise it will handle graceful termination on
-// SIGINT or SIGTERM and return nil.
-func Serve(h http.Handler, serverConfig *ServerConfig, addr string) (err error) {
+func (config *ServerConfig) buildHTTPServer(h http.Handler, addr string) (*http.Server, error) {
 	var tlsConfig *tls.Config
-	if serverConfig != nil {
-		if serverConfig.TLS != nil {
-			tlsConfig, err = serverConfig.TLS.TLSConfig()
+	var err error
+	if config != nil {
+		if config.TLS != nil {
+			tlsConfig, err = config.TLS.TLSConfig()
 			if err != nil {
-				return err
+				return nil, err
 			}
-			h, err = serverConfig.TLS.TLSAuthWrapper(h)
+			h, err = config.TLS.TLSAuthWrapper(h)
+			if err != nil {
+				return nil, err
+			}
+		}
+
+		// If TrustedForwarders is defined, rewrite the request
+		// headers using X-Forwarded-Proto and X-Real-IP.
+		if len(config.TrustedForwarders) > 0 {
+			h, err = newProxyHeaders(h, config.TrustedForwarders)
 			if err != nil {
-				return err
+				return nil, err
 			}
 		}
 
-		if serverConfig.MaxInflightRequests > 0 {
-			h = newLoadSheddingWrapper(serverConfig.MaxInflightRequests, h)
+		// If MaxInflightRequests is set, enable the load
+		// shedding wrapper.
+		if config.MaxInflightRequests > 0 {
+			h = newLoadSheddingWrapper(config.MaxInflightRequests, h)
 		}
 	}
 
 	// These are not meant to be external-facing servers, so we
 	// can be generous with the timeouts to keep the number of
 	// reconnections low.
-	srv := &http.Server{
+	return &http.Server{
 		Addr:         addr,
 		Handler:      instrumentHandler(h),
 		ReadTimeout:  30 * time.Second,
 		WriteTimeout: 30 * time.Second,
 		IdleTimeout:  600 * time.Second,
 		TLSConfig:    tlsConfig,
+	}, nil
+}
+
+// Serve HTTP(S) content on the specified address. If config.TLS is
+// not nil, enable HTTPS and TLS authentication.
+//
+// This function will return an error if there are problems creating
+// the listener, otherwise it will handle graceful termination on
+// SIGINT or SIGTERM and return nil.
+func Serve(h http.Handler, config *ServerConfig, addr string) error {
+	srv, err := config.buildHTTPServer(h, addr)
+	if err != nil {
+		return err
 	}
 
 	// Install a signal handler for gentle process termination.
@@ -80,7 +100,7 @@ func Serve(h http.Handler, serverConfig *ServerConfig, addr string) (err error)
 	}()
 	signal.Notify(sigCh, syscall.SIGINT, syscall.SIGTERM)
 
-	if tlsConfig != nil {
+	if srv.TLSConfig != nil {
 		err = srv.ListenAndServeTLS("", "")
 	} else {
 		err = srv.ListenAndServe()