headers_in_hash

[Maxim Dounin]

Hello!

On Tue, Feb 18, 2014 at 02:36:24PM -0500, atarob wrote:

> Maxim Dounin Wrote:
> -------------------------------------------------------
> > Hello!
> > 
> > On Fri, Feb 14, 2014 at 04:39:23PM -0500, atarob wrote:
> > 
> > > Creating a module, I want to read in from config desired http header
> > fields.
> > > Then, during config still, I want to get the struct offset for the
> > fields
> > > that have dedicated pointers in the header_in struct. It seems that
> > when I
> > > access headers_in_hash from the main config,  it is uninitialized. I
> > can see
> > > in the code that there is
> > > 
> > > ngx_http_init_headers_in_hash(ngx_conf_t *cf,
> > ngx_http_core_main_conf_t
> > > *cmcf)
> > > 
> > > in ngx_http.c. It seems to be called when the main conf is being
> > generated
> > > though I am not certain yet.
> > > 
> > > Where and when exactly is headers_in_hash initialized? If I wanted
> > to read
> > > from it during ngx_http_X_merge_loc_conf(), what would I need to do?
> >  Or am
> > > I supposed to do it at some point later?
> > 
> > The cmcf->headers_in_hash is expected to be initialized during 
> > runtime.  As of now, it will be initialized before  
> > postconfiguration hooks, but I wouldn't recommend relaying on 
> > this.
> > 
> > I also won't recommend using cmcf->headers_in_hash in your own 
> > module at all, unless you have good reasons to.  It's not really a 
> > part of the API, it's an internal entity which http core uses to 
> > do it's work.
> 
> There is an API? I thought the only way to figure out nginx was to read
> source? But seriously, I didn't land on any API doing a google search. 

API != documentation

> API aside, is the point of this hash not to do faster lookups for fields
> that become needed at runtime (say from config) as opposed to compile time?
> Otherwise, to look for N fields, I have to do N*M comparisons as I iterate
> through the fields, right? I was trying to avoid that. Is there a better
> way?

The point of this hash is to do special processing of certain 
headers in http core.  If you want to do something similar in your 
own module, you may want to create your own hash.

-- 
Maxim Dounin
http://nginx.org/