how to gracefully resolve problems in bad filters?

[Stas Bekman <st...@stason.org>]

Any filter must always send something down-stream, this something should 
be at least an empty bucket brigade.

If the input filter doesn't send anything down the stream, apache asserts:

[Thu Jan 16 15:49:56 2003] [crit] [Thu Jan 16 15:49:56 2003] file 
http_protocol.c, line 1915, assertion "!(((&(bb)->list))->next == (struct 
apr_bucket *)((char *)((&(bb)->list)) - ((long) (((char *) (&(((struct 
apr_bucket*)((void *)0))->link))) - ((char *) ((void *)0))))))" failed

and segfaults:

#0  0x402f58b1 in kill () from /lib/i686/libc.so.6
#1  0x402f56a8 in raise () from /lib/i686/libc.so.6
#2  0x402f6a96 in abort () from /lib/i686/libc.so.6
#3  0x080c2c5b in ap_log_assert () at log.c:716
#4  0x08097281 in ap_get_client_block () at http_protocol.c:1893
#5  0x405f5eab in mpxs_ap_get_client_block (my_perl=0x8d27968, r=0x8d6da48,
     buffer=0x8be8a84, bufsiz=8192)
     at 
/home/stas/apache.org/modperl-2.0/xs/Apache/RequestIO/Apache__RequestIO.h
:139
#6  0x405f6681 in XS_Apache__RequestRec_get_client_block (my_perl=0x8d27968,
     cv=0x8711934) at RequestIO.xs:45
#7  0x404ca9c7 in Perl_pp_entersub (my_perl=0x8d27968) at pp_hot.c:2603
#8  0x404a7afd in Perl_runops_debug (my_perl=0x8d27968) at dump.c:1394
#9  0x404517a1 in S_call_body (my_perl=0x8d27968, myop=0xbfffefe0, is_eval=0)
     at perl.c:1931
#10 0x4045134d in Perl_call_sv (my_perl=0x8d27968, sv=0x8d73d08, flags=4)
     at perl.c:1849
#11 0x40410712 in modperl_callback (my_perl=0x8d27968, handler=0x8c8dac8,
     p=0x8d6da10, r=0x8d6da48, s=0x8118a90, args=0x8d626b4)
     at modperl_callback.c:53
#12 0x40410e05 in modperl_callback_run_handlers (idx=6, type=4, r=0x8d6da48,
     c=0x0, s=0x8118a90, pconf=0x0, plog=0x0, ptemp=0x0)
     at modperl_callback.c:185
...

which is not so nice. For streaming filters we could have a flag that will 
be off if nothing was printed, but there is no way to know whether the 
filter is implemented using the streaming api or not. More-over one can 
switch APIs in the same filter. If this flag is on, we could send an empty 
bb downstream.

I suppose that things similar with output filters.

I'll add a test that reproduces a problem (but commented out) and if 
anybody has an idea how to handle it gracefully, please speak up.

__________________________________________________________________
Stas Bekman            JAm_pH ------> Just Another mod_perl Hacker
http://stason.org/     mod_perl Guide ---> http://perl.apache.org
mailto:stas@stason.org http://use.perl.org http://apacheweek.com
http://modperlbook.org http://apache.org   http://ticketmaster.com


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