iPhone OS 4.0: NSFileHandleDataAvailableNotification not providing callback at file-end

Question

I'm a bit new to iPhone development, so be gentle! I'm supporting an app which loads a wav file from a URL file-stream, and plays it back through an AudioQueue.

We run a continual loop in another thread, and stop the Queue if we detect that it has no buffers in use, and the input FileStream has reached its end. In turn, we detect if the FileStream has ended within the waitForDataInBackgroundAndNotify callback on the NSFileHandleDataAvailableNotification for the stream, by checking whether the availableData has length 0.

This works under iOS 3.0 - we get a notification of 0 available data at the end of the file - but on iOS 4.0, we don't seem to receive the callback at file end. This happens on an OS 4.0 device, regardless of the target OS version.

Has the API changed between the two versions? How can I detect the end of the file now?

Hopefully-relevant code:

data-available callback:

- (void)readFileData:(NSNotification *)notification
{
  @try
  {
    NSData *data = [[notification object] availableData];

    if ([data length] == 0 && self.audioQueueState != AQS_END)
    {
      /***********************************************************************/
      /* We've hit the end of the data but it's possible that more may be    */
      /* appended to the file (if we're still downloading it) so we need to  */
      /* wait for the availability of more data.                             */
      /***********************************************************************/
      [self setFileStreamerState:FSS_END];
      [[notification object] waitForDataInBackgroundAndNotify];
    }
    else if (self.audioQueueState == AQS_END)
    {
      TRC_DBG(@"ignore read data as ending");
    }
    else
    {
      NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

      TRC_DBG(@"Read %d bytes", [data length]);

      [self setFileStreamerState:FSS_DATA];

      if (discontinuous)
      {
        TRC_DBG(@"AudioFileStreamParseBytes %d bytes, discontinuous", [data length]);
        err = AudioFileStreamParseBytes(audioFileStream, [data length], [data bytes], kAudioFileStreamParseFlag_Discontinuity);
        discontinuous = NO;
      }
      else
      {
        TRC_DBG(@"AudioFileStreamParseBytes %d bytes, continuous", [data length]);
        err = AudioFileStreamParseBytes(audioFileStream, [data length], [data bytes], 0);
      }

      /***********************************************************************/
      /* If error then get out, otherwise wait again for more data.          */
      /***********************************************************************/
      if (err != 0)
      {
        [self failWithErrorCode:AS_FILE_STREAM_PARSE_BYTES_FAILED];
      }
      else
      {
        [[notification object] waitForDataInBackgroundAndNotify];
      }

      [pool release];
    }
  }
  @catch (NSException *exception)
  {
    TRC_ERR(@"Exception: %@", exception);
    TRC_ERR(@"Exception reason: %@", [exception reason]);
    //[self failWithErrorCode:AS_FILE_AVAILABLE_DATA_FAILED];
  }
}