Header duplicated in case of NGINX and NodeJS

[cecile.saintmartin@…]

We're using NGINX on 2 servers :
First one (Front server): NGINX + NodeJS
Second one (Backend server) : NGINX + other application

The request goes through the first server to the backend server, this part is Ok.
When the backend returned the reponse, NGINX add a "Vary" header.
Then the response goes back through NodeJS on the Front server. NodeJs lower case all headers (native behaviour) => the header "Vary" is transformed into "vary" (header name).
Then the response goes back on NGINX on the front server and NGINX add a second header "Vary".
So finally we have to headers : one "Vary" and one "vary".
This behaviour has been observed with other header : X-ForwardedFor for example.
So it seems that NGINX doesn't detect the existing header "vary" and add a new one.
We consider it as a bug because according to RFC, header names are case INSENSITIVE.

[Maxim Dounin]

Duplicate of #875.