Method ReverseProxy

coderd/tailnet.go:189–251

(targetURL, dashboardURL *url.URL, agentID uuid.UUID, app appurl.ApplicationURL, wildcardHostname string)

}

func (s *ServerTailnet) ReverseProxy(targetURL, dashboardURL *url.URL, agentID uuid.UUID, app appurl.ApplicationURL, wildcardHostname string) *httputil.ReverseProxy {
	// Rewrite the targetURL's Host to point to the agent's IP. This is
	// necessary because due to TCP connection caching, each agent needs to be
	// addressed invidivually. Otherwise, all connections get dialed as
	// "localhost:port", causing connections to be shared across agents.
	tgt := *targetURL
	_, port, _ := net.SplitHostPort(tgt.Host)
	tgt.Host = net.JoinHostPort(tailnet.TailscaleServicePrefix.AddrFromUUID(agentID).String(), port)

	proxy := httputil.NewSingleHostReverseProxy(&tgt)
	proxy.ErrorHandler = func(w http.ResponseWriter, r *http.Request, theErr error) {
		var (
			desc           = "Failed to proxy request to application: " + theErr.Error()
			additionalInfo = ""
			actions        = []site.Action{}
		)

		var tlsError tls.RecordHeaderError
		if (errors.As(theErr, &tlsError) && tlsError.Msg == "first record does not look like a TLS handshake") ||
			errors.Is(theErr, http.ErrSchemeMismatch) {
			// If the error is due to an HTTP/HTTPS mismatch, we can provide a
			// more helpful error message with redirect buttons.
			switchURL := url.URL{
				Scheme: dashboardURL.Scheme,
			}
			_, protocol, isPort := app.PortInfo()
			if isPort {
				targetProtocol := "https"
				if protocol == "https" {
					targetProtocol = "http"
				}
				app = app.ChangePortProtocol(targetProtocol)

				switchURL.Host = fmt.Sprintf("%s%s", app.String(), strings.TrimPrefix(wildcardHostname, "*"))
				actions = append(actions, site.Action{
					URL:  switchURL.String(),
					Text: fmt.Sprintf("Switch to %s", strings.ToUpper(targetProtocol)),
				})
				additionalInfo += fmt.Sprintf("This error seems to be due to an app protocol mismatch, try switching to %s.", strings.ToUpper(targetProtocol))
			}
		}

		site.RenderStaticErrorPage(w, r, site.ErrorPageData{
			Status:      http.StatusBadGateway,
			Title:       "Bad Gateway",
			Description: desc,
			Actions: append(actions, []site.Action{
				{
					Text: "Retry",
				},
				{
					URL:  dashboardURL.String(),
					Text: "Back to site",
				},
			}...),
			AdditionalInfo: additionalInfo,
		})
	}