write
Description:
Attempts to write buffer.length bytes from buffer to this.
 If some data is successfully written, the return status will be OK,
      and *nwrote will contain the number of bytes actually written (which may be less than buffer.length).
If this is non-blocking, and no data could be written right away, the return value will be WOULD_BLOCK. In this case, the caller can connect to the writable signal to know when more data can be written. (NB: writable is only emitted after write returns WOULD_BLOCK, and it is only emitted once. See the documentation for non_blocking.)
Parameters:
| this | 
           the socket  | 
      
| buffer | 
           data to write  | 
      
| nwrote | 
           on return, number of bytes written  | 
      
| cancellable | 
           a Cancellable, or   | 
      
| len | 
           size of   | 
      
Returns:
| 
           a SocketIOStatus, as described above (or 
            EOF or 
            ERROR.   |