Error: readv() failed (104: Connection reset by peer) while reading upstream

Question

I have facebook apps with flask with nginx and uwsgi. When it receive POST from facebook, it always has error:

readv() failed (104: Connection reset by peer) while reading upstream

But when I access my apps directly (with GET method), it ran smoothly. What I've done:

1. Limit @app.route with POST method only - doesn't work.
2. Add limit in wsgi: uwsgi_buffer_size (in case request from facebook is big), and uwsgi_harakiri (in case uwsgi provide timeout before finish it request) - doesn't work.

I have workaround in django but can't figure out yet how to implement in flask. Could anyone help please?

Stjohn

the answer is bit ridiculous for me. I have to process all post data, even if my process is doing nothing. if "nothing" not in request.form: pass. Its working.. Btw, facebook open the app with POST request, so I should add that for every route. There must be better way of doing it.. – Stjohn

If there is datas on a socket you have to read them (no other choices). On the flask wiki you can find a middleware to bypass this common problem on proxied setup: flask.pocoo.org/snippets/47 uWSGI can help you with the --post-buffering option, but it is only a shortcut, nothing magic in it. – Pretext

Answer 1

This is the bug of uwsgi. You can get more from [uWSGI] Several bugs .

The simple solution is that you must read the POST body by wsgi.input, even through POST body is null or you don't need POST params.

Harneen

this has nothing to do with uWSGI (and it is certainly not a bug). Closing a socket without reading datas in it, is a wrong programming behaviour. uWSGI can help you (if you do not want to change your code) buffering post datas automatically via the --post-buffering option. – Pretext

@Pretext Thank you. When add post-buffering option in uwsgi setting, it works. But in some cases, for example, post request has no params, it's not need to read post body from wsgi.input. So I don't think it's the programmers' mistake. – Harneen

Answer 2

The issue is that "upstream" (the actual process that nginx is proxing) is closing the connection.

In my case, Django is my web server and I needed to set DATA_UPLOAD_MAX_NUMBER_FIELDS to be larger because there were too many fields in the POST request.

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