php_stream_copy_to_stream() attempts to read up to maxlen
bytes of data from src and write them to dest,
and returns the number of bytes that were successfully copied.
If you want to copy all remaining data from the src stream, pass the
constant PHP_STREAM_COPY_ALL as the value of maxlen.
Note: This function will attempt to copy the data in the most efficient manner, using memory mapped files when possible.