detecting user abort with output buffering enabled in PHP

The Notes section in the function documentation of ignore_user_abort() suggest that PHP cannot detect that a user has aborted the r开发者_JS百科equest if no data is sent to the client. This is true for the function connection_status(), too. Unfortunately, I need to detect a user abort (an ajax request that can be cancelled) on a page which makes use of output buffering (and I cannot change that easily.)

Is there any other way of detecting a user abort except using the function connection_status()? Or any specific way to make that function return the correct value? PHP should actually know that the request was aborted, since a FIN packet is received from the client.

I have already tried analyzing the stream metadata of php://input, php://output, php://stdin and php://stdout after reading/writing data in a blocking and non-blocking manner before and after the connection was aborted, but that didn't provide any useful state changes.

Silly suggestion, but ... have you tried sending some data to the client, followed by a flush() before you start the output buffering? The only other solution I can think of is to escape the buffer(s), but I can imagine how it could be quite troublesome, as you said.

Maybe a helper to assist with breaking the buffer ...

function OBWanCallback($buffer)
{
    if( OBWan::$isFinished )
    {
        // -- Actual callbacks go here ...
    }

   return $buffer;
}

OBWan::startbuffer('OBWanCallback');
[ // -- Example functionality
    self::$callback = $callback;
    ob_start(self::$callback);
]

// -- in some code far, far away ...

OBWan::suspendbuffer();
[ // -- Example functionality
    self::$buffercache = ob_get_clean();
]

echo " ";
flush();

OBWan::resumebuffer();
[ // -- Example functionality
    ob_start(self::$callback);
    echo self::$buffercache;
    self::$buffercache = "";
]

// -- in some code far, far away ...

OBWan::outputbuffer();
[
    self::$isFinished = true;
    return ob_get_clean();
]

with something to account for the depth of buffers you've implemented, if you have implemented depth.