Function serveHTTP

main.go:218–281

nolint:cyclop //TODO reduce complexity here.

(rw http.ResponseWriter, r *http.Request)

//nolint:cyclop //TODO reduce complexity here.
func serveHTTP(rw http.ResponseWriter, r *http.Request) {
	switch r.Method {
	case http.MethodGet, http.MethodPost:
		// Only GET and POST methods are supported.
	case http.MethodOptions:
		// This is required for CORS shit :)
		rw.Header().Set("Allow", "GET,POST")
		return
	default:
		err := fmt.Errorf("%q: unsupported method %q", r.RemoteAddr, r.Method)
		rw.Header().Set("Connection", "close")
		respondWith(rw, err, http.StatusMethodNotAllowed)
		return
	}

	switch r.URL.Path {
	case "/favicon.ico":
	case "/metrics":
		// nolint:forcetypeassert // We will cover this by tests as we control what is stored.
		an := allowedNetworksMetrics.Load().(*config.Networks)
		if !an.Contains(r.RemoteAddr) {
			err := fmt.Errorf("connections to /metrics are not allowed from %s", r.RemoteAddr)
			rw.Header().Set("Connection", "close")
			respondWith(rw, err, http.StatusForbidden)
			return
		}
		proxy.refreshCacheMetrics()
		promHandler.ServeHTTP(rw, r)
	case "/", "/query", pingEndpoint:
		var err error

		if r.URL.Path == pingEndpoint && !allowPing.Load() {
			err = fmt.Errorf("ping is not allowed")
			respondWith(rw, err, http.StatusForbidden)
			return
		}

		// nolint:forcetypeassert // We will cover this by tests as we control what is stored.
		proxyHandler := proxyHandler.Load().(*ProxyHandler)
		r.RemoteAddr = proxyHandler.GetRemoteAddr(r)

		var an *config.Networks
		if r.TLS != nil {
			// nolint:forcetypeassert // We will cover this by tests as we control what is stored.
			an = allowedNetworksHTTPS.Load().(*config.Networks)
			err = fmt.Errorf("https connections are not allowed from %s", r.RemoteAddr)
		} else {
			// nolint:forcetypeassert // We will cover this by tests as we control what is stored.
			an = allowedNetworksHTTP.Load().(*config.Networks)
			err = fmt.Errorf("http connections are not allowed from %s", r.RemoteAddr)
		}
		if !an.Contains(r.RemoteAddr) {
			rw.Header().Set("Connection", "close")
			respondWith(rw, err, http.StatusForbidden)
			return
		}
		proxy.ServeHTTP(rw, r)
	default: