SseStream shouldn't set "Transfer-Encoding" to "identity"

[ashervb]

Bug Report

Transfer-Encoding likely should be set to "chunked", if I understand correctly. This only seems to be an issue when running behind particular reverse-proxies. As of RFC 7230, "identity" is not a thing anymore, and we are probably off-spec for any other value. nginx only supports "chunked" anyway.

In my particular case, NestJS application running behind Traefik, this results in the following error net/http: HTTP/1.x transport connection broken: unsupported transfer encoding: identity

Possible Solution

nest/packages/core/router/sse-stream.ts

  pipe<T extends HeaderStream>(destination: T, options?: { end?: boolean }): T {
    if (destination.writeHead) {
      destination.writeHead(200, {
        // See https://github.com/dunglas/mercure/blob/master/hub/subscribe.go#L124-L130
        'Content-Type': 'text/event-stream',
        Connection: 'keep-alive',
        // Disable cache, even for old browsers and proxies
        'Cache-Control':
          'private, no-cache, no-store, must-revalidate, max-age=0, no-transform',
        'Transfer-Encoding': 'identity',
        Pragma: 'no-cache',
        Expire: '0',
        // NGINX support https://www.nginx.com/resources/wiki/start/topics/examples/x-accel/#x-accel-buffering
        'X-Accel-Buffering': 'no',
      });
      destination.flushHeaders();
    }

    destination.write(':\n');
    return super.pipe(destination, options);
  }

Replace "identity" with "chunked"

Environment

• Nest version: 7.6.15
• Node version: 15.14.0
• Platform: Linux

[jmcdo29]

Would you like to make a PR for this? Seems like a good change overall

[ashervb]

Yes - created #6889

[kamilmysliwiec]

Thanks! Let's track this here #6889