Is it possible to get route info in request middleware?

[rjmackay]

I want to get the parameterized route path in my request middleware so I can use it for tracing. Is this possible?

[manimovassagh]

Request middleware in TanStack Start runs at the server/Nitro level before the router has matched a route, so the parameterized route path isn't directly available there.

However, you can extract it from the request URL yourself. A couple of approaches:

1. Parse the URL manually in the middleware

If you know your route patterns, you can match against them:

// app/middleware.ts
import { createMiddleware } from "@tanstack/react-start"

export const tracingMiddleware = createMiddleware().server(async ({ next, request }) => {
  const url = new URL(request.url)
  const pathname = url.pathname

  // Map to your parameterized patterns for tracing
  const routePattern = matchRoutePattern(pathname)
  
  // Use routePattern for your tracing span name
  console.log(`[trace] ${routePattern} -> ${pathname}`)

  return next()
})

function matchRoutePattern(pathname: string): string {
  // Simple example — match /users/123 -> /users/:id
  if (/^\/users\/[^/]+$/.test(pathname)) return "/users/:id"
  if (/^\/posts\/[^/]+\/comments$/.test(pathname)) return "/posts/:id/comments"
  return pathname
}

2. Use route-level middleware instead

If you need the actual matched route info, use beforeLoad on individual routes (or a shared layout route). At that point the router has matched and you have access to route params and the route ID:

// routes/__root.tsx
export const Route = createRootRoute({
  beforeLoad: ({ location, context }) => {
    // location.pathname is available
    // Route.id gives you the route identifier
    startTrace(Route.id, location.pathname)
  },
})

Or create a shared beforeLoad helper and apply it to a layout route that wraps everything:

// routes/_layout.tsx
export const Route = createFileRoute("/_layout")({
  beforeLoad: ({ location, matches }) => {
    // matches gives you the matched route chain
    const leafRoute = matches[matches.length - 1]
    console.log(`Route: ${leafRoute.routeId}, Path: ${location.pathname}`)
  },
})

3. Server function middleware with context

If your tracing is specifically for server functions, you can attach route info from the component side via headers or context that the server function reads.

The short answer: request middleware is intentionally low-level and route-agnostic. For route-aware tracing, beforeLoad on a layout route is the way to go.