Optimize memory usage for Http Adapter

[romainneutron]

$content = str_replace('\/', '/', $content); consumes a lot of memory, especially with large payloads.

In my import loop, it was consuming 40MB per bulk.

This improves memory consumption

[ruflin]

Thanks for the PR to make the code faster. Can you please update the CHANGELOG.md file? Adding a test to confirm the optimization of this can is quite tricky, but it looks very reasonable :-)

One question that this raised on my side is, why do we have JSON_ELASTICSEARCH at all? I looks like we could replace it everywhere with JSON_UNESCAPED_UNICODE https://github.com/ruflin/Elastica/blob/master/lib/Elastica/JSON.php#L59 My assumption is we needed it for some historical reasons (PHP version compatibility).

[romainneutron]

Would you like a test to cover the optimization or the slashes unescaping?
If you would like an optimization demonstration, I'd be glad to share a Blackfire profile

[ruflin]

The changed code is already covered by quite a few other integration tests I assume as it is such a central part. So I worry not too much that it breaks the code. No need to share the Backfire profile, the changes make a lot of sense. I fully trust you here :-)

In case you have an easy test to add feel free to add it, but not required. Only additional thing required is the update to the CHANGELOG.md

[ruflin]

@romainneutron I merged this change as I plan to do a release. I will add the changelog entry.

[romainneutron]

Thanks a lot, sorry for being a bit slow on this one

[ruflin]

@romainneutron No worries. Thanks a lot for the contribution.