Re: calling ap_get_brigade with nonempty brigade

[Stas Bekman]

Joe Schaefer wrote:
ap_http_filter seems to assume it will receive an empty 
brigade from its caller. The problem is around lines 
1028 - 1035 in http_protocol.c:

    rv = ap_get_brigade(f->next, b, mode, block, readbytes);

    if (rv != APR_SUCCESS) {
        return rv;
    }
    /* How many bytes did we just read? */
    apr_brigade_length(b, 0, &totalread);
totalread is only accurate in this context if b was 
empty to begin with.  Is this is a bug in ap_http_filter?
I think that assumptions is valid for all filters and is correct by (an 
undocumented) design.

If I understand things correctly, If you want to re-use some older bbs (e.g. 
from previous invocations or if you have an underrun and ask for more during 
the same invocation), you should create a new bb, pass it to ap_get_brigade() 
and then merge with the previous one.

Here is a snippet from t/filter/TestFilter/in_bbs_underrun.pm, though I rip 
the data off, rather than merge.

    # fetch and consume bucket brigades untill we have at least SIZE
    # bytes to work with
    do {
        my $tbb = APR::Brigade->new($filter->r->pool, $ba);
        my $rv = $filter->next->get_brigade($tbb, $mode, $block, $readbytes);
        ($data, $seen_eos) = flatten_bb($tbb);
        $tbb->destroy;
        $buffer .= $data;
    } while (!$seen_eos && length($buffer) < SIZE);
it should be pretty much the same in C.

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Stas Bekman            JAm_pH ------> Just Another mod_perl Hacker
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