reverseproxy: Reset Content-Length to prevent fastcgi from hanging

[trea]

…PHP-FPM requests from hanging

See: #5420

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[mholt]

Awesome @trea -- thank you for the PR!

Since this patch essentially reverts a reversion, can you help us verify that all the following issues are not a problem with this patch:

• Transfer-Encoding: chunked causing php_fastcgi to hang #5236
• Caddy 2.6.3 high memory usage #5366
• v2.6.4 php-fpm gets stuck in read state #5420

I have my hands full today so it might be fastest if you are able to confirm these -- but anyone else is welcome to test as well!

[trea]

Sure thing!

#5236 and #5420 should be fixed by this
#5366 should remain fixed by this because this patch still requires buffering to be enabled

But I do have more related thoughts I'm about to post in #5420. The TL;DR being that I think Caddy may need to implement buffering in its FastCGI transport for reverse proxying.

[mholt]

(Left a comment in the issue as well.)

I think this is starting to converge on the right solution -- and is a step forward, now that I fixed the OOM bug that I introduced 😅

I like your idea that probably the FastCGI transport should buffer anyway, so it doesn't have to be explicitly enabled, but this is at least a step back in the right direction.