Re: sub filter‘s bug?

[Maxim Dounin]

Hello!

On Tue, Sep 21, 2010 at 05:08:08PM +0800, Simon Liu wrote:

> i find this result  is cause by postpone filter is removed. because i
> use --without-http_ssi_module config nginx. and i read nginx config find
> this   in  auto/modules:
> 
> if [ $HTTP_SSI = YES ]; then
>     HTTP_POSTPONE=YES
> fi
> 
> 
> if [ $HTTP_ADDITION = YES ]; then
>     HTTP_POSTPONE=YES
> fi
> 
> and why  postpone is yes when ssi or addition module is on ?

Postpone filter is used to order data sent by subrequests.  It 
shouldn't be needed when no subrequests are used.

> and then i debug nginx find some code in ngx_http_postpone_filter method :
> 
>     if (r->postponed == NULL) {
> 
>         if (in || c->buffered) {
>             return ngx_http_next_filter(r->main, in);
>         }
> 
>         return NGX_OK;
>     }
> 
> therefore if no postpone module, sub filter module may emerge the result in
> my previous email  .
> 
> On Wed, Sep 15, 2010 at 11:00 AM, Simon Liu <simohayha.bobo at gmail.com>wrote:
> 
> > my nginx version is 0.7.67.
> >
> > I test nginx's sub filter, there have some alert log in error log:
> >
> > *the http output chain is empty while sending response to client.*
> > *
> > *
> > and  i debug nginx , and then found this is cause by sub filter. so  i read
> >  sub filter's source.
> >
> > in  ngx_http_sub_body_filter:
> >
> >   *  if (ctx->once && (ctx->buf == NULL || ctx->in == NULL)) {*
> > *
> > *
> > *        if (ctx->busy) {*
> > *            if (ngx_http_sub_output(r, ctx) == NGX_ERROR) {*
> > *                return NGX_ERROR;*
> > *            }*
> > *        }*
> > *
> > *
> > *        return ngx_http_next_body_filter(r, in);*
> > *    }*
> >
> > i found when  sub_filter_once is on , after  text have replaced . and the
> > second enter ngx_http_sub_body_filter.
> > At the moment when in is null,ctx->busy is not null,and so *ngx_http_sub_output
> >  may send  *the rest of* buf  completely**,  therefore in  **ngx_http_next_body_filter
> > will log alert log : the http output chain is empty while sending response
> > to client. *
> > *
> > *
> > *i*n conclusion I *think  there should add a *judgement that in is whether
> > or not NULL.
> > *
> > *
> > *this is my patch:*
> > *
> > *
> > *
> > --- nginx-0.7.67/src/http/modules/ngx_http_sub_filter_module.c 2009-10-26
> > 23:54:29.000000000 +0800
> > +++ nginx-0.7.67_new/src/http/modules/ngx_http_sub_filter_module.c 2010-09-15
> > 10:14:04.996666685 +0800
> > @@ -187,16 +187,16 @@ ngx_http_sub_body_filter(ngx_http_reques
> >      }
> >
> >      if (ctx->once && (ctx->buf == NULL || ctx->in == NULL)) {
> >
> >          if (ctx->busy) {
> > -            if (ngx_http_sub_output(r, ctx) == NGX_ERROR) {
> > -                return NGX_ERROR;
> > -            }
> > +            rc = ngx_http_sub_output(r, ctx);
> >          }
> >
> > -        return ngx_http_next_body_filter(r, in);
> >  +        if (rc != NGX_ERROR && in != NULL)
> > +            return ngx_http_next_body_filter(r, in);
> > +        return rc;

This will use uninitialized rc when no ctx->busy.

Maxim Dounin