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authorEric Wong <e@80x24.org>2019-09-26 00:36:27 +0000
committerEric Wong <e@80x24.org>2019-09-26 00:36:27 +0000
commita6c9366f6d8ebb0a8716a198c4e40bb339aef766 (patch)
treecdd8ba36bd5fda63a612907b446554a783a3e3f3 /script/public-inbox.cgi
parent17bec61580fe1eab9b60b01d990af9046a1cb031 (diff)
downloadpublic-inbox-a6c9366f6d8ebb0a8716a198c4e40bb339aef766.tar.gz
httpd: disable Deflater middleware by default on Perl <5.18 p516-leak
Testing with perl-5.16.3-294.el7_6 RPM package on RHEL/CentOS 7,
the Deflater middleware triggers a leak when used in conjunction
with our push-based responses from PublicInbox::Qspawn.

I could not find another solution to workaround the memory leak
in this case, and I could not find a specific leak fix in
the perl5180delta manpage[1] which looked like it would
solve our problem.

Attempting to workaround the issue proved futile.  Using
internal Deflater-specific keys to prevent deflating in
GitHTTPBackend and Qspawn did not solve the problem:

        $env->{"plack.skip-deflater"} = 1;
        $env->{"psgix.no-compress"} = 1;

Nor did forcing an invalid encoding via "git fetch":

	git -c http.extraheader=Accept-Encoding:gzap fetch

So this appears to be a problem with Plack::Util::response_cb
somewhere.

This does NOT appear to be a problem with ref() leaking as in
DS::next_tick[2], since I couldn't find where
Plack::Middleware::Deflater or Plack::Util::response_cb would be
calling ref() on a blessed reference to trigger a leak.

Also, oddly enough, the ref() use for backwards compatibility at
the top of PublicInbox::GitHTTPBackend::serve does NOT seem to
trigger a leak on 5.16.3 due to [2]:

	# XXX compatibility... ugh, can we stop supporting this?
	$git = PublicInbox::Git->new($git) unless ref($git);

[1] https://perldoc.perl.org/perl5180delta.html
[2] https://rt.perl.org/Public/Bug/Display.html?id=114340
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