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Posted to dev@httpd.apache.org by Jim Carlson <jc...@jnous.com> on 2003/03/14 09:50:29 UTC

ap_get_brigade question

Howdy,
   I have a question in the same vein as my last post.  Can I rely on 
ap_get_brigade(mode=AP_MODE_READBYTES, len=X) to return a brigade of length no 
greater than X?  It would appear not, which means I need to be prepared to set 
aside extra bytes...  But I thought this was exactly what the supplying filter 
was supposed to do!  Confirmation requested.

Thanks!

Jim

Re: ap_get_brigade question

Posted by Jim Carlson <jc...@jnous.com>.

Thanks.  I noticed that my perception of a problem was wrong -- I was calling 
ap_rgetline multiple times with the same brigade, without calling 
apr_brigade_cleanup in between (or something like that).  Bytes were left over 
from the previous request when the second one returned.

Jim

Greg Stein wrote:
> On Tue, Mar 18, 2003 at 04:45:09PM -0800, Justin Erenkrantz wrote:
> 
>>--On Friday, March 14, 2003 12:50 AM -0800 Jim Carlson <jc...@jnous.com> 
>>wrote:
>>
>>
>>>Howdy,
>>>   I have a question in the same vein as my last post.  Can I rely on
>>>ap_get_brigade(mode=AP_MODE_READBYTES, len=X) to return a brigade of length
>>>no greater than X?  It would appear not, which means I need to be prepared
>>>to set aside extra bytes...  But I thought this was exactly what the
>>>supplying filter was supposed to do!  Confirmation requested.
>>
>>A filter could hypothetically ignore AP_MODE_READBYTES's len parameter and 
>>return more.  But, none of the current filters in our core do this - they will 
>>return at most X bytes.  I believe we take the position if a filter returns 
>>more than X in this case, it is broken.  So, it should be a good assumption to 
>>make.  -- justin
> 
> 
> Yes, it would be considered broken. The higher-level filter knows the
> boundaries, and how much to ask for (or not). The lower-level filters do not
> and cannot have the knowledge that the higher/application filters have.
> 
> Thus, the rule is that a filter never returns more than asked.
> 
> [ there are ways to change that, but it isn't in the architecture now ]
> 
> Cheers,
> -g
>

Re: ap_get_brigade question

Posted by Greg Stein <gs...@lyra.org>.

On Tue, Mar 18, 2003 at 04:45:09PM -0800, Justin Erenkrantz wrote:
> --On Friday, March 14, 2003 12:50 AM -0800 Jim Carlson <jc...@jnous.com> 
> wrote:
> 
> > Howdy,
> >    I have a question in the same vein as my last post.  Can I rely on
> > ap_get_brigade(mode=AP_MODE_READBYTES, len=X) to return a brigade of length
> > no greater than X?  It would appear not, which means I need to be prepared
> > to set aside extra bytes...  But I thought this was exactly what the
> > supplying filter was supposed to do!  Confirmation requested.
> 
> A filter could hypothetically ignore AP_MODE_READBYTES's len parameter and 
> return more.  But, none of the current filters in our core do this - they will 
> return at most X bytes.  I believe we take the position if a filter returns 
> more than X in this case, it is broken.  So, it should be a good assumption to 
> make.  -- justin

Yes, it would be considered broken. The higher-level filter knows the
boundaries, and how much to ask for (or not). The lower-level filters do not
and cannot have the knowledge that the higher/application filters have.

Thus, the rule is that a filter never returns more than asked.

[ there are ways to change that, but it isn't in the architecture now ]

Cheers,
-g

-- 
Greg Stein, http://www.lyra.org/

Re: ap_get_brigade question

Posted by Justin Erenkrantz <ju...@erenkrantz.com>.

--On Friday, March 14, 2003 12:50 AM -0800 Jim Carlson <jc...@jnous.com> 
wrote:

> Howdy,
>    I have a question in the same vein as my last post.  Can I rely on
> ap_get_brigade(mode=AP_MODE_READBYTES, len=X) to return a brigade of length
> no greater than X?  It would appear not, which means I need to be prepared
> to set aside extra bytes...  But I thought this was exactly what the
> supplying filter was supposed to do!  Confirmation requested.

A filter could hypothetically ignore AP_MODE_READBYTES's len parameter and 
return more.  But, none of the current filters in our core do this - they will 
return at most X bytes.  I believe we take the position if a filter returns 
more than X in this case, it is broken.  So, it should be a good assumption to 
make.  -- justin