what does the "main" pointor in request struct mean?

[4everpan]

Igor Sysoev Wrote:
-------------------------------------------------------
> On Thu, May 27, 2010 at 02:55:57AM -0400, 4everpan
> wrote:
> 
> > I found in Nginx that:
> > struct ngx_http_request_s {
> >     ...
> >     ngx_http_request_t               *main;
> >     ...
> > };
> > what does this argument mean?
> > 
> > I also found a similar argument in Apache:
> > request_rec* request_rec::main  
> > //Pointer to the main request if this is a
> sub-request (see http_request.h) 
> > 
> > so,
> > Do they have the same meaning?
> > and if yes, what dose a main request and a
> sub-request mean?  What's the difference between
> the 2 http requests?
> 
> Yes, this is the same as in Apache.
> Subrequests are requests made inside a request,
> for example, in SSI:
> 
>     <!--# include virtual="/header.html" -->
> 
> 
> -- 
> Igor Sysoev
> http://sysoev.ru/en/
> 
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It's really a surprise for me that Igor Sysoev answered my first question in our forum!   \(^o^)/~  

But I'm not familiar with SSI or shtml protocal...  So... let me think about it:
When I enter the URL "http://www.g.cn" into IE, the URL will be redirected to "http://www.google.cn" such as follows:

Started	Time	Sent	Received	Method	Result	Type			URL
+ 0.000	0.134	406	532	GET	301	Redirect to http://www.google.cn/webhp?source=g_cn	http://www.g.cn/

Dose the GET of  URL"http://www.google.cn/webhp?source=g_cn" is a sub-request of the GET of URL"http://www.g.cn/"?

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,90805,91363#msg-91363