Modules programming. Several questions. $variables, URI rewriting.

[Maxim Dounin]

Hello!

On Tue, Mar 16, 2010 at 07:20:47PM -0400, mriadus wrote:

> 1. I can set a handler to one of several "phases", like: 
> "NGX_HTTP_REWRITE_PHASE", "NGX_HTTP_CONTENT_PHASE" and other. 
> How to define an order the handlers will be called inside the 
> same "phase"? Lets suppose i bond several handlers to some phase 
> and what will be called first? If that order is depends on order 
> of modules "loading", how to define that order of modules 
> loading?

Order of modules within phase is currently defined only by order 
in which modules were added during configure.

> 2. I developed a module that creates new variable "$z" during 
> initialization. That variable can be used in configuration file. 
> When nginx meets $z in configuration file, my handler is 
> invoking (handler that returning the content of $z). If 
> configuration file has three occurrences in the configuration 
> file, my handler called 3 times. But i have a situation: the 
> handler is calling 2 times per one variable. So it called 6 
> times for 3 occurrences of $z. Why? (that handler is called 
> "get_handler").

During evaluation of complex values variable obtained 2 times: to 
find out it's length and to find out it's content.  It doesn't 
normally lead to two calls to handler though.  The fact that 
your handler is called 2 times indicate that you don't set valid 
or not_found flags on returned variable correctly.

> 3. OK. Lets suppose (2) is resolved. I want to create the 
> content of $z once per request, but the "get_handler" can be 
> invoked N times for the same request. Where i can set the 
> content of $z between "get_handler" invocations for the same 
> request?

Any content returned correctly will be cached for the rest of 
request (unless variable caching is explicitly disabled via 
appropriate flags guring variable creation or in it's handler).

> 4. I want to rewrite the ARGS from the request: i need to add 
> "&z=1" to the end of args. For example: "a=1&b=1" ---> 
> "a=1&b=2&z=1". But inside the handler i have access to 
> ngx_http_request_t via pointer. And i have access to that ARGS 
> via member "args" of the structure "ngx_http_request_t". That 
> "args" member is a "ngx_str_t". How can i change its length? I 
> tried to create a new string and rewrite old pointer (r -> args 
> = new_str_ptr), but it is not working.

Changing r->args should work as long as done correctly (assigning 
a pointer to r->args isn't correct one as it's not pointer, you 
have to set r->args.data and r->args.len).

Note well: you may also want to set r->valid_unparsed_uri = 0 if 
you are changing args.

> Seems to be i have a copy 
> of request during handler invocation and nginx killing that copy 
> after request is processed?

No.

Maxim Dounin

p.s. It's probably a good idea to ask such questions in 
nginx-devel@ mailing list instead, CC'd.