code: public UnsignedInteger32 postWriteRequest(byte[] handle, long position,
  			byte[] data, int off, int len) throws SftpStatusException,
  			SshException {
  
  		if ((data.length - off) < len) {
  			throw new IndexOutOfBoundsException("Incorrect data array size!");
  		}
  
  		try {
  			UnsignedInteger32 requestId = nextRequestId();
  			Packet msg = createPacket();
  			msg.write(SSH_FXP_WRITE);
  			msg.writeInt(requestId.longValue());
  			msg.writeBinaryString(handle);
  			msg.writeUINT64(position);
  			msg.writeBinaryString(data, off, len);
  
  			sendMessage(msg);
  
  			return requestId;
  		} catch (SshIOException ex) {
  			throw ex.getRealException();
  		} catch (IOException ex) {
  			throw new SshException(ex);
  		}
  	}
docs: Send a write request for an open file but do not wait for the response
  from the server.
  
  @param handle
  @param position
  @param data
  @param off
  @param len
  @return UnsignedInteger32
  @throws SshException