This represents a file that we are writing to, and therefore is mutable.
// PHP's fread() buffer is set to 8192 by default
const CHUNK = 8192;
`$fp` (private) - File pointer
`int $pos` (private) - Position within the stream (via `ftell()`)
`array $stat` (private) - Statistics about the file (via `fstat()`)
`$file` - Either a string containing a file location or a resource (file
handle opened by `fopen()`)
int $num) :
Read the desired number of bytes from the internal stream, preventing partial
int $i = 0)
Set the current position in the stream to the desired value.
int $num = null) :
$buf to the internal stream.