The use of php://temp/maxmemory as a stream counts towards the memory usage of the script; you are not specifying a new memory pool by using this type of stream.
As noted in the documentation however, this stream type will start to write to a file after the specified maxmemory limit is exceeded. This file buffer is NOT observed by the memory limit.
This is handy if you want your script to have a reasonably small memory limit (eg 32MB) but but still be able to handle a huge amount of data in a stream (eg 256MB)
The only works if you use stream functions like fputs(); if you use $buffer .= 'string'; or $buffer = $buffer . 'string'; you're calling your stream data back into PHP and this will hit the limiter.
As a practical example:
<?php
ini_set('memory_limit', '0.5M');
$buffer = fopen('php://temp/maxmemory:1048576', 'r+');
$x = 0;
while ($x < 1*1024*1024) {
fputs($buffer, 'a');
$x++;
}
echo "This will never be displayed";
?>
However, change fopen to use php://temp/maxmemory:1 (one byte, rather than one megabyte) and it will begin writing to the unlimited file stream immediately, avoiding memory limit errors.
