Accessing subrequest output in memory

[Peter Leonov]

On 16.10.2010, at 18:49, Eugaia <ngx.eugaia at gmail.com> wrote:

> Hi Peter,
>
> Thanks.  What Yichun is referring to there is how echo issues  
> subrequests, however I was just testing with the basic 'echo'  
> commands.  The thing is that no special handling of data is made  
> when it is 'in memory'.  This appears to be a *feature* of Nginx -  
> the in-memory handling needs to be done by specific modules, and  
> currently the only one that seems to do this properly is the  
> upstream module.  The FastCGI and WSGI modules explicitly say that  
> they don't work with r->subrequest_in_memory set.
>
> I think the best solution appears to be to create an output filter,  
> then save the output chain to a module-specific context struct.   
> This should then work properly with all modules, and the in-memory  
> flag can be removed so that it will work with FastCGI, WSGI etc too.
And it will work, JS module does just that. The apropriate code was  
partly copied from the core of postpone filter.

>
> Thanks,
>
> Marcus.
>
> On 16/10/2010 10:29, Peter Leonov wrote:
>> Hi Marcus,
>>
>> On 16.10.2010, at 4:44, Eugaia <ngx.eugaia at gmail.com> wrote:
>>
>>> Hi again,
>>>
>>> I've found the output that the module I'm trying to get this to  
>>> work with (ngx_http_echo_module) sent the content directly to the  
>>> parent request.  I'm not sure if this is as a result of a generic  
>>> feature, or something that should be fixed in echo - which I'll  
>>> look into.
>>
>> AFAICT, this is by desing. Yichun wrote about it in nearest past:
>> http://agentzh.spaces.live.com/Blog/cns!FF3A735632E41548!552.entry
>>
>>>
>>> Cheers,
>>>
>>> Marcus.
>>>
>>> On 15/10/2010 20:59, Eugaia wrote:
>>>> Hi,
>>>>
>>>> I'm trying to get the output of an in-memory subrequest, but I  
>>>> can't find where the output is stored.
>>>>
>>>> Basically, I'm doing :
>>>>
>>>> ...
>>>> ngx_uint_t flags;
>>>> ngx_http_post_subrequest_t *psr;
>>>> ngx_str_t location;
>>>> ngx_str_t *url_args;
>>>>
>>>> psr->handler = my_callback;
>>>> flags |= NGX_HTTP_SUBREQUEST_IN_MEMORY;
>>>>
>>>> ngx_http_subrequest (r, &location, url_args, &sr, psr, flags);
>>>> ...
>>>>
>>>> // waiting for for subrequest to process
>>>>
>>>> my_callback (ngx_http_request_t *sr, void *data, ngx_int_t rc)
>>>> {
>>>>   ngx_http_request_t *r;
>>>>
>>>>   r = sr->parent;
>>>>   ...
>>>>   // I want to be able to access the (body) output from the  
>>>> subrequest here
>>>> }
>>>>
>>>> If the subrequest uses an upstream, I know I can access the  
>>>> output using sr->upstream->buffer.  However, if the subrequest  
>>>> does not use upstreams, then this won't work.  The output is not  
>>>> available from sr->out - r->out is set to NULL at some point  
>>>> during the output filtering.  As far as I can make out, what I  
>>>> need to do is find where the body output ngx_chain_t * struct is  
>>>> saved after all the body filtering has been processed, but I'm  
>>>> struggling to find it.
>>>>
>>>> Can anyone tell me where it is, or where I can find the output?
>>>>
>>>> Note : I don't want to remove the in-memory flag because I don't  
>>>> want the output flushed to the client.
>>>>
>>>> Thanks,
>>>>
>>>> Marcus.
>>
>> Best regards,
>> Peter.
>>
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