Function newPassthroughRouter

aibridge/passthrough.go:27–77

newPassthroughRouter returns a simple reverse-proxy implementation which will be used when a route is not handled specifically by a [intercept.Provider]. A single reverse proxy is created per provider and reused across all requests.

(prov provider.Provider, logger slog.Logger, m *metrics.Metrics, tracer trace.Tracer)

// by a [intercept.Provider].
// A single reverse proxy is created per provider and reused across all requests.
func newPassthroughRouter(prov provider.Provider, logger slog.Logger, m *metrics.Metrics, tracer trace.Tracer) http.HandlerFunc {
	provBaseURL, err := url.Parse(prov.BaseURL())
	if err != nil {
		return newInvalidBaseURLHandler(prov, logger, m, tracer, err)
	}
	if _, err := url.JoinPath(provBaseURL.Path, "/"); err != nil {
		return newInvalidBaseURLHandler(prov, logger, m, tracer, err)
	}

	// Transport tuned for streaming (no response header timeout).
	t := &http.Transport{
		Proxy:                 http.ProxyFromEnvironment,
		ForceAttemptHTTP2:     true,
		MaxIdleConns:          100,
		IdleConnTimeout:       90 * time.Second,
		TLSHandshakeTimeout:   10 * time.Second,
		ExpectContinueTimeout: 1 * time.Second,
	}

	// Build the passthrough proxy, reused across all requests for this provider.
	// Rewrite sets proxy headers. For centralized requests, KeyFailoverTransport
	// handles auth and failover. BYOK requests pass through.
	proxy := &httputil.ReverseProxy{
		Rewrite: func(pr *httputil.ProxyRequest) {
			rewritePassthroughRequest(pr, provBaseURL)
		},
		Transport: keypool.NewKeyFailoverTransport(
			apidump.NewPassthroughMiddleware(t, prov.APIDumpDir(), prov.Name(), logger, quartz.NewReal()),
			prov.KeyFailoverConfig(logger),
		),
		ErrorHandler: func(rw http.ResponseWriter, req *http.Request, e error) {
			if _, ok := errors.AsType[*http.MaxBytesError](e); ok {
				writeRequestBodyTooLarge(rw)
			} else {
				logger.Warn(req.Context(), "reverse proxy error", slog.Error(e), slog.F("path", req.URL.Path))
				http.Error(rw, "upstream proxy error", http.StatusBadGateway)
			}
		},
	}

	return func(w http.ResponseWriter, r *http.Request) {
		if m != nil {
			m.PassthroughCount.WithLabelValues(prov.Name(), r.URL.Path, r.Method).Add(1)
		}

		ctx, span := startSpan(r, tracer)
		defer span.End()

		proxy.ServeHTTP(w, r.WithContext(ctx))
	}
}

// rewritePassthroughRequest configures the outbound request for the upstream and
// applies proxy headers.