How to cancel user upload in Formidable (Node.js)?

Question

I have been working on this problem for two days now, and I am stuck. I am using Node.js with Express, and I am trying to implement an upload form. Basically, I want the form to

Answer 1

To abort the upload, the proper thing to do is close the socket.

req.socket.end();

Unfortunately, the situation where a server wants to abort an in-progress HTTP upload is a mess.

The proper, spec-compliant thing to do here is simply send a HTTP 413 response early – that is, as soon as you detect that the client has sent more bytes than you want to handle. It is up to you whether or not you terminate the socket after sending the error response. This is in line with RFC 2616. [...] What happens next is not ideal.

• If you leave the socket open, all browsers (Chrome 30, IE 10, Firefox 21) will keep sending data until the entire file is uploaded. Then and only then, the browser will display your error message. This really sucks since the user must wait for the entire file to complete the upload, only to find out the server rejected it. It also wastes your bandwidth.

  The browsers' current behavior is in violation of RFC 2616 § 8.2.2:

  An HTTP/1.1 (or later) client sending a message-body SHOULD monitor the network connection for an error status while it is transmitting the request. If the client sees an error status, it SHOULD immediately cease transmitting the body. If the body is being sent using a "chunked" encoding (section 3.6), a zero length chunk and empty trailer MAY be used to prematurely mark the end of the message. If the body was preceded by a Content-Length header, the client MUST close the connection.

  There are open Chrome and Firefox issues, but don't expect a fix any time soon.

• If you close the socket immediately after sending the HTTP 413 response, all browsers will obviously stop uploading immediately, but they currently show a "connection reset" error (or similar), not any HTML you might send in the response.

  Again, this is probably a violation of the spec (which allows the server to send a response early and close the connection), but I wouldn't expect browser fixes any time soon here either.

The fact you're seeing a loop of POST requests is suspect. Are you using some kind of AJAX uploader? It may be automatically retrying the upload after you close the socket early.