Install

$ npm install --save node-drivers-layer

Methods

close(callback)

Calls the disconnect method of the layer and all upper layers. The callback is called once the layer and all upper layers are finished closing.

Example Usage

layer.close(function() {
  console.log('closed');
});

send(message, info, priority, context)

Use this method to send data to a lower layer.

getNextRequest()

See overridable method sendNextMessage() for example usage.

contextCallback(callback [, context])

Helper method. Handles saving a callback for a certain identifier/context. A context is created (just an integer) if it is not passed to the method.

Currently used for PCCC/DF1 commands and connected CIP messages. For sending PCCC commands, a context, in this case the transaction number, is embeded in the request. The context is saved in an internal map as the key and the callback is saved as the value. The same transaction number is embeded in the response that is received some time later. This transaction number is used to grab the callback from the internal map. The callback is then called and passed the data received.

Example from PCCC/DF1

wordRangeRead(address, callback) {
  if (callback == null) return;

  let transaction = this._incrementTransaction();
  let message = PCCCPacket.WordRangeReadRequest(transaction, address);

  this.send(message, null, false, this.contextCallback(function(data) {
    // this callback is callad from handleData
    let reply = PCCCPacket.fromBufferReply(data);
    let error = getError(reply.status);
    if (error != null) {
      callback(error);
    } else {
      callback(null, reply.Data);
    }
  }, transaction));
}

handleData(data) {
  let packet = PCCCPacket.fromBufferReply(data);
  let callback = this.getCallbackForContext(packet.transaction);
  if (callback != null) {
    callback(data);
  }
}

Overridable Methods

sendNextMessage()

This method is called when an upper layer sends a message.

Example Usage

class MyLayer extends Layer {
  sendNextMessage() {
    let request = this.getNextRequest();
    if (request != null) {
      let message = request.message; // Buffer
      let info = request.info; // Information passed from the upper layer

      // do something with message prior to sending
      buffer = encapsulate(message);

      this.send(buffer);

      // don't forget to call sendNextMessage!
      this.sendNextMessage();
    }
  }
}

handleData(data, info, context)

This method is called when data is forwarded from a lower layer. For example, a TCP-layer forwarding data up to an EIP-layer.

disconnect(callback)

Use to close any connections and cleanup resources. Call the callback function when finished.