# Suggestion about expansibility of the data

**URL:** <https://www.ruby-forum.com/t/suggestion-about-expansibility-of-the-data/170840>\
**Category:** NGINX\
**Created:** [June 23, 2009, 12:16pm UTC](https://www.ruby-forum.com/t/suggestion-about-expansibility-of-the-data/170840 "2009-06-23T12:16:31Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Chieu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/54ee81/32.png) [@Chieu](https://www.ruby-forum.com/u/Chieu)\
**Post date:** [June 23, 2009, 12:16pm UTC](https://www.ruby-forum.com/t/suggestion-about-expansibility-of-the-data/170840/1 "2009-06-23T12:16:31Z")

</div>

hi, developers  
Because of the modularity of nginx, I can extend the new function  
easily.  
But there are some requirements which need to modify the original source  
code.  
For example:  
I want to add a variable which records the count of requests sent to  
each  
upstream. And I must add a variable into the struct  
“ngx\_http\_upstream\_rr\_peer\_t”, when round robin get the upstream ,the  
variable++ . This way, I shoud modify the source code of the upstream  
module.  
I think if the struct “ngx\_http\_upstream\_rr\_peer\_t” have a reserved  
pointer(void \*), which reserved for others developing new modules.  
Totally, I think the modularity of nginx just resolved the expansibility  
of  
function. But if the I want to expand some import data like the struct  
“ngx\_http\_request\_t”, I must modify the original source code. And if  
some  
important struct adds a reserved pointer, I think the data of nginx will  
be  
easily be extend.

thanks.

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<div class="post-metadata">

**Author:** ![Chieu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/54ee81/32.png) [@Chieu](https://www.ruby-forum.com/u/Chieu)\
**Post date:** [June 23, 2009, 12:41pm UTC](https://www.ruby-forum.com/t/suggestion-about-expansibility-of-the-data/170840/2 "2009-06-23T12:41:47Z")

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Hello!

On Tue, Jun 23, 2009 at 06:05:19PM +0800, Chieu wrote:

> hi, developers  
> Because of the modularity of nginx, I can extend the new function easily.  
> But there are some requirements which need to modify the original source  
> code.  
> For example:  
> I want to add a variable which records the count of requests sent to each  
> upstream. And I must add a variable into the struct  
> “ngx\_http\_upstream\_rr\_peer\_t”, when round robin get the upstream ,the  
> variable++ . This way, I shoud modify the source code of the upstream  
> module.

You may easily write transparent upstream balancer module that  
does this (just counts and passes everything to the real  
balancer). Without nginx code modifications. It’s not really  
efficient due to extra function calls, but it will work.

> I think if the struct “ngx\_http\_upstream\_rr\_peer\_t” have a reserved  
> pointer(void \*), which reserved for others developing new modules.  
> Totally, I think the modularity of nginx just resolved the expansibility of  
> function. But if the I want to expand some import data like the struct  
> “ngx\_http\_request\_t”, I must modify the original source code. And if some  
> important struct adds a reserved pointer, I think the data of nginx will be  
> easily be extend.

I don’t really understand the question, but for any data you may  
use either your module context (every module has pointer to it’s  
context stored in ngx\_http\_request\_t) or variables (if you need  
something that survives internal redirects).

Maxim D.

---

<div class="post-metadata">

**Author:** ![Chieu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/54ee81/32.png) [@Chieu](https://www.ruby-forum.com/u/Chieu)\
**Post date:** [June 23, 2009, 2:32pm UTC](https://www.ruby-forum.com/t/suggestion-about-expansibility-of-the-data/170840/3 "2009-06-23T14:32:40Z")

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the way of the module context can meet many requitments. But some others  
can’t be implemented by the module way.  
for example,  
In the struct"ngx\_http\_upstream\_rr\_peer\_t", I want add a variable to  
count  
how many times I haved request this upstream.  
If there is a reserved pointer, I can use it point a struct I have  
defined  
in my module. But now,I must modify the source code and when I want to  
replace with a new version nginx, I have to re-modifiy the code.

ngx\_http\_request\_t can expand datas with the module context, but other  
data  
struct can’t use module conext?

thank you

2009/6/23 Maxim D. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)

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<div class="post-metadata">

**Author:** ![Chieu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/54ee81/32.png) [@Chieu](https://www.ruby-forum.com/u/Chieu)\
**Post date:** [June 23, 2009, 3:46pm UTC](https://www.ruby-forum.com/t/suggestion-about-expansibility-of-the-data/170840/4 "2009-06-23T15:46:04Z")

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Hello!

On Tue, Jun 23, 2009 at 08:26:27PM +0800, Chieu wrote:

> the way of the module context can meet many requitments. But some others  
> can’t be implemented by the module way.  
> for example,  
> In the struct"ngx\_http\_upstream\_rr\_peer\_t", I want add a variable to count  
> how many times I haved request this upstream.  
> If there is a reserved pointer, I can use it point a struct I have defined  
> in my module. But now,I must modify the source code and when I want to  
> replace with a new version nginx, I have to re-modifiy the code.

As I said, there is no need to modify nginx code. Feel free to  
wrap balancer module, allocate additional memory in  
peer.init\_upstream() handler and increment numbers on wrapped  
peer.get() handler.

For simple wrapper around take a look at  
ngx\_http\_upstream\_ip\_hash\_module. For a bit more complex wrapper  
see ngx\_http\_upstream\_keepalive\_module here:

[http://mdounin.ru/hg/ngx\_http\_upstream\_keepalive/file/tip/ngx\_http\_upstream\_keepalive\_module.c](http://mdounin.ru/hg/ngx_http_upstream_keepalive/file/tip/ngx_http_upstream_keepalive_module.c)

> ngx\_http\_request\_t can expand datas with the module context, but other data  
> struct can’t use module conext?

Basically in nginx you either work with request (and here you have  
module contexts to store your data) or with configuration (and  
module configs to store your data). Most things could be easily  
done by pure modules without patching nginx itself, and there are  
lots of examples in nginx source code how to do it.

Maxim D.

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<div class="post-metadata">

**Author:** ![Chieu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/54ee81/32.png) [@Chieu](https://www.ruby-forum.com/u/Chieu)\
**Post date:** [June 24, 2009, 4:40am UTC](https://www.ruby-forum.com/t/suggestion-about-expansibility-of-the-data/170840/5 "2009-06-24T04:40:37Z")

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hello!  
I have understood it.  
But why the proxy cache module add the “cache” variable in  
ngx\_http\_request\_t? It can also be done in the module context.

thanks.

2009/6/23 Maxim D. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)