Header handling

Rafa_F · August 14, 2015, 6:51pm

Hi,

I have a few questions regarding headers in nginx:

I use proxy_set_header to pass a header to upstream servers. Is it
possible to honor the header if the incoming request already has it?
I want to pass the “Server” header from upstream response to clients,
and if there is no such response header, I’d like to add a customer one.
Is
it possible via core nginx or any third party modules? Currently I am
using
“proxy_pass_header Server” without any check. I am not sure what happens
if
upstream response doesn’t have it.
I am trying to log an upstream response header to access log but it
has
a “dot” in it (say X.header). I don’t have any control to the upstream
servers. On nginx side, I tried setting “ignore_invalid_headers off” in
the
server block, and in the logformat, I tried a few things for the the
column: $upstream_http_x.header $upstream_http_x_header
$upstream_http_x-header, but nothing works. Any ideas how I can log it?

Thanks!
Frank

fjlj · August 14, 2015, 7:37pm

Hi,

Use mapped variable

map $http_ $ {
“” “value if nit set”;
default $http_;
}
Then you can set header with the new variable.

I guess you can use map, too. Use $upstream_http_name instead.
Sorry, I have no idea on this.

fjlj · August 14, 2015, 10:04pm

Thanks ryd994 for the suggestion! 1 and 2 are working now.
Anyone else has any ideas on 3?

Frank

fjlj · August 15, 2015, 9:16am

I made the below patch and can now use $upstream_http_x_header for
logformat to capture the header X.header in the access log. Does anybody
see any issues with the patch?

— src/http/ngx_http_variables.c.orig 2015-08-15 02:19:31.635328112
+0000

+++ src/http/ngx_http_variables.c 2015-08-15 02:19:42.051541422 +0000

@@ -897,6 +897,8 @@

         } else if (ch == '-') {

             ch = '_';

```
       } else if (ch == '.') {
```

           ch = '_';

       }



       if (var->data[n + prefix] != ch) {

Thanks!
Frank

fjlj · August 17, 2015, 1:32pm

Hello!

On Sat, Aug 15, 2015 at 12:15:47AM -0700, Frank L. wrote:

         } else if (ch == '-') {

             ch = '_';

```
       } else if (ch == '.') {
```
```
           ch = '_';

       }
```

Such approach will likely result in security problems, as
“X.header” and “X-header” would be indistinguishable from nginx
point of view.

–
Maxim D.
http://nginx.org/

fjlj · August 18, 2015, 1:39am

Hi Maxim,

Thanks for you comment! Do you have any other approaches/suggestions?
I use nginx as a proxy/load-balancer. The request will be processed by
the
upstream java servers. I assume my change won’t actually modify the
actual
header, so upstream will still get the original header and can
distinguish
. and - ?

Regards,
Frank