Use temp stream instead of string to buffer content

[yookoala]

• Update MultipartStreamBuilder::build to buffer built content
  in a php://temp stream resource instead of (string) $contents.
  This way, the size of the stream built won't be limited by PHP
  runtime limit.

Q	A
Bug fix?	yes
New feature?	no
BC breaks?	no
Deprecations?	no
Related tickets
Documentation	Fully backward compatible without any interface changes. Only internal programming changes.
License	MIT

What's in this PR?

Rewrite to append stream contents and boundaries into a "php://temp" stream as a buffer. Contents within predefined limit (2MB) will be handled in memory for speed. Otherwise, PHP will create a temp file for storage. This mean the multipart stream size is virtually without size limit (unless if, of course, your harddisk is full).

Why?

The original MultipartStreamBuilder::build would read everything into a string variable $streams before making it another stream. If the total size of the content exceed the PHP's memory limit, the process would fail.

Checklist

• Updated CHANGELOG.md to describe BC breaks / deprecations | new feature | bugfix
• Documentation pull request created (if not simply a bugfix)

[dbu]

looks good to me. i can imagine that this adds some filesystem overhead for medium sized streams where previously things worked in memory and now go to the temporary file, but if people really need to worry on that level they can configure the temp handling, according to php.net

@GrahamCampbell do you agree or are there any doubts?

[yookoala]

Updated by PR to include mechanism to detect available memory and assign maxmemory to the buffer (size of buffer suitable to stay in memory).

It would subtract from memory_get_usage() result from PHP memory_limit to get the available memory. Then use 1/4 as the maxmemory setup of the "php://temp" stream used for buffering.

I also added a setBufferMaxMemory() public method for overriding this.

[dbu]

this is really cool! i think using max 1/4 of available memory by default is a good idea to not use up all the memory with large streams.

[yookoala]

Finally fixed all the style issues :-)

[dbu]

cheers, looks good to me. i wait until tomorrow so @Nyholm or @GrahamCampbell get a chance to see it before merging.

@yookoala could you please add a changelog note for this improvement?

[GrahamCampbell]

I've left some comments. There are some issues, some of which are major (but easy to resolve).

[Nyholm]

Thank you

I agree that we should use a stream, but lets fallback to PHP default behavior.

[GrahamCampbell]

@Nyholm has suggested some excellent changes. 👍

[dbu]

looks good to me, thanks!

[Nyholm]

Cool. Im really happy with this now.

[GrahamCampbell]

Good work.