How to modfiy headers in and headers out

Yingyuan Cheng yingyuan at
Thu Nov 1 06:22:22 MSK 2007

Hello Igor.

I tracked executing path using gdb, found the content of param "r" 
(ngx_http_request_t) past by hook routine was a awful mess, and 
r.headers_out.headers.last pointed to 0x22, which was in a protected 
memory region. When executing path left my module and went to other 
modules, the same param "r" was in its normal status. After I changed 
the module code layout, such as moving "#include <openssl/md5>" after 
nginx including headers, the problem diminished. Is it a compiling 
problem? The configuring line is:

CFLAGS="-g" ./configure --with-debug 

ngx_http_sessid_filter_module "borrows" code snippets from 
ngx_http_userid_filter_module and ngx_http_upstream_ip_hash_module. 
First it acts as a load balancer, dispatching requests to backends based 
on cookie. If the cookie not found in request, it'll generate a new one. 
Then in the filter phase, it sends the cookie to client if it was 
generated newly in balancing phase. So we can make the client always 
dispatched to the same backend.

Another question I want to ask: May I change request headers_out in 
upstream_init_peer phase?

Thank you very much.

Best Regards


Igor Sysoev 写道:
> On Wed, Oct 31, 2007 at 07:45:39PM +0800, Yingyuan Cheng wrote:
>> After changed the order of my filter module defined in
>> objs/ngx_modules.c which should go after ngx_http_header_filter module,
>> it works. But I still get a segment fault when calling
>> ngx_list_push(&r->headers_out.headers) in filter hook function.
>> Anyone could give me a explanation?
>> Thanks very much.
> ngx_list_push(&r->headers_out.headers) should not cause segfault in this phase.
> Could you show more code ?

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