QoS Bandwidth Throttle in PHP

This class can be used to limit (throttle) the speed of files served for download.

It intercepts the PHP script output by setting a buffering handler that is called every time a given number of bytes are served to the browser.

The class measures the time since the last time the PHP output buffer was flushed and hold on PHP for a while if the average download speed is above a given limit.

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There are three different bandwidth shaping mechanisms to ensure adequate Quality of Service:

1) burst transfer rate will be switched off after sending X bytes to the user (this can be helpful to send small images quickly, and limit the download speed of huge files)

2) burst transfer rate will be switched off after given period of time in seconds, then it will revert to the standard throttle speed

3) burst transfer rate will not be activated at all, the download speed limit will be constant during the whole downloading process (in this case $config->burstLimit must be equal to the $config->rateLimit)