Add output buffer length check before attempting to end it

[kexxt]

Hello, this PR is related to #704. Please let me know if any tests need to be adjusted.

Thank you!

[staabm]

This fix looks bogus to me. I think you should investigate why/when this zlib error happens (e.g. in php-src)

[kexxt]

Got it, I appreciate your input.

[denis-sokolov]

I’m not sure it’s obviously bogus. We want to call ob_end_clean as long as there’s buffering present. ob_get_length and ob_get_level both seem like valid options to detect that, and if one’s more practical, we could use it.

It’d be nice to understand the root cause of it better. 🤔

[staabm]

ob_get_level returns the number of nested output buffers (how many times ob_start() was called).
ob_get_length returns the number of bytes of the current active output buffer, no matter how nested the ob_start() calls are.

I think thats a totally different thing

[kexxt]

Basically I reach a point where ob_get_length returns 0 but ob_get_level returns 2. When it tries to ob_get_clean, zlib error occurs.

[denis-sokolov]

@staabm, sure, they do different things, but they both are good candidates to use in that conditional. After all, is it correct to keep flushing until we have no flushing enabled or until we have nothing buffered? Not obvious to me.