Hi Maxim & Jeroen,

I'm the user Jeroen mentioned. I'm sorry for only being to produce sporadic errors earlier, I now made a test case which reliably produces
the error, both on our server and Jeroen's server (so it's hopefully not just my amateur status with nginx).

Of course, the ridiculously large proxy settings were only chosen in desperation, but I can now report that no increase of proxy buffer
settings solves the problem at all (or shifts the treshold at which the error messages occur). So I think it's safe to say the error message
upstream sent too big header while reading response header from upstream
is misleading (unless the CORS headers that Jeroen added are somehow inflated through the POST request, wouldn't know why that would be).


I can also now rule out that's its due to the headers sent or received.

I receive only the following headers when the 502s occur

HTTP/1.1 100 Continue

HTTP/1.1 502 Bad Gateway
Server: nginx/1.4.4
Date: Mon, 10 Feb 2014 10:46:57 GMT
Content-Type: text/html
Content-Length: 172
Connection: keep-alive

And I sent only these

POST /ocpu/library/base/R/identity HTTP/1.1
Host: ourhost.xx
Accept: */*
Content-Length: 3545
Content-Type: application/x-www-form-urlencoded
Expect: 100-continue


I do send a large request, 2241 characters (inlined JSON-ified data), but that is not near the upper limit of POST request as I know them.

Here's the issue on the openCPU github, where I uploaded my test cases (sorry for it being a bit primitively done, I'm in a bit of a tight spot time-wise here and just an amateur):
https://github.com/jeroenooms/opencpu/issues/76