denoland/deno · error · TypeError

Invalid response

Error message

Invalid response

What it means

trySetServeFastStaticResponse is an internal fast path used when a handler returns a response carrying Deno's private serveFast* symbol marks (set by optimized Response creation paths). It switches on an internal header-kind tag, and the default branch throws 'Invalid response' when that tag holds a value outside the known SERVE_FAST_HEADER_* enum. Standard user code cannot reach this state through public APIs; it signals an internal invariant break.

Source

Thrown at ext/http/00_serve.ts:532

      op_http_set_response_body_static_with_default_header(req, body, status);
      return true;
    case SERVE_FAST_HEADER_CONTENT_TYPE:
      op_http_set_response_body_static_with_content_type(
        req,
        body,
        status,
        response[serveFastContentTypeKey],
      );
      return true;
    case SERVE_FAST_HEADER_NONE:
      if (typeof body === "string") {
        op_http_set_response_body_text(req, body, status);
      } else {
        op_http_set_response_body_bytes(req, body, status);
      }
      return true;
    default:
      throw new TypeError("Invalid response");
  }
}

// Report an error that was thrown while a streaming response body was being
// drained. The response status/headers are already on the wire at this point,
// so the value returned from `onError` can no longer be used; we route the
// error through the handler purely so it is observed (the default handler logs
// a stack trace) instead of being silently swallowed.
function reportResponseStreamError(onError, error) {
  let result;
  try {
    result = onError(error);
  } catch (e) {
    internals.log("error", "Exception in onError while handling exception", e);
    return;
  }
  if (ObjectPrototypeIsPrototypeOf(PromisePrototype, result)) {
    PromisePrototypeThen(result, undefined, (e) => {

View on GitHub (pinned to 89f33cbef2)

Solutions

1. Remove code that manipulates Deno internal symbols and return plain Response objects
2. Update to the latest Deno patch release in case the fast-path tagging was fixed
3. As a stopgap, rebuild the response before returning it: new Response(body, response) so no fast marks are present
4. If it reproduces with public APIs only, file a minimal repro at github.com/denoland/deno

// Wrap the whole request path; this error indicates an internal invariant break
Deno.serve(async (req) => {
  try {
    return await handler(req);
  } catch (err) {
    return new Response("Internal Server Error", { status: 500 });
  }
});

When it happens

Trigger: Code that manually writes Deno internal symbols (Deno[Deno.internal], serveFastStatusKey/serveFastHeaderKindKey) onto an object with an invalid header-kind value, or a regression inside Deno's optimized Response path itself.

Common situations: Experiments or monkey-patching that touch Deno.internal, or hitting a Deno bug in an unreleased/nightly build's fast-response optimization.

Related errors

• ${prefix}Linter plugin must be an object
• Already upgraded
• Already closed
• Request closed
• Return value from serve handler must be a response or a prom

AI-assisted analysis of denoland/deno@89f33cbef2 (2026-08-16). Data as JSON: /api/errors/958fd14b95b7b535. Report an issue: GitHub.