Removing a request header in an access phase handler

[Maxim Dounin]

Hello!

On Tue, Jul 09, 2013 at 12:13:37AM +0200, Jan Algermissen wrote:

> Hi Maxim,
> 
> thanks, question inline:
> 
> On 08.07.2013, at 19:59, Maxim Dounin <mdounin at mdounin.ru> wrote:
> 
> > Hello!
> > 
> > On Mon, Jul 08, 2013 at 06:45:33PM +0200, Jan Algermissen wrote:
> > 
> >> Hi,
> >> 
> >> I developing a handler for the access phase. In this handler I 
> >> intend to remove a certain header.
> >> 
> >> It seems that this is exceptionally hard to do - the only hint I 
> >> have is how it is done in the headers_more module.
> >> 
> >> However, I wonder, whether there is an easier way, given that it 
> >> is not an unusual operation.
> > 
> > Removing request headers from a request isn't something supported 
> > by nginx.
> > 
> > What is supported is filtering/modification of headers passed to 
> > upstream servers with proxy_set_header (fastcgi_param, ...).
> > 
> > E.g., this is how proxy module provies a way to add 
> > X-Forwarded-For header.  It implements the $proxy_add_x_forward_for 
> > variable, which is expected to be used in a config like this:
> > 
> >   proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
> > 
> >> If not, I'd greatly benefit from a documentation of the list and 
> >> list-part types. Is that available somewhere? Seems hard to 
> >> figure out all the bits and pieces that one has to go through to 
> >> cleanly remove an element from a list.
> > 
> > Try looking into src/core/ngx_list.[ch] for a documentation in C.  
> > It doesn't really support elements removal though.
> 
> Yes, I could provide a list_remove implementation - problem is, 
> I think that the request->headers_in convenience fields point to 
> elements of the .headers list, yes? Given that list elts is an 
> array, re-organizing that array would invalidate the pointers of 
> headers_in.
> 
> Right ow, I think that renaming the header in question and 
> setting the headers_in field to null is probably the only 
> option.
> 
> What do you think?

Quoting myself:

: Removing request headers from a request isn't something 
: supported by nginx.

If you are going to remove request headers - first of all, you 
should understand that what you are doing is a hack.  And asking 
me what do I think is a bit pointless - I think it's a hack. :)

-- 
Maxim Dounin
http://nginx.org/en/donation.html