function _parseMessage()

in device/transport/mqtt/src/mqtt.ts [1080:1144]

• 42 lines of code
• 12 McCabe index (conditional complexity)

function _parseMessage(topic: string, body: any): MethodMessage {
  let url: URL.Url;
  let path: string[];
  let query: any;
  try {
    url = URL.parse(topic);
    path = url.path.split('/');
    query = querystring.parse(url.query as string);
  } catch (err) {
    debugErrors('Could not parse topic for received message: ' + topic);
    debugErrors('Error is ' + err);
    return undefined;
  }

  // if the topic has a querystring then 'path' will include it; so
  // we strip it out
  const lastPathComponent = path[path.length - 1];
  if (lastPathComponent.indexOf('?') !== -1) {
    path[path.length - 1] = lastPathComponent.substr(
      0, lastPathComponent.indexOf('?')
    );
  }

  if (path.length > 0 && path[0] === '$iothub') {
    const message = new MethodMessageImpl();
    if (path.length > 1 && path[1].length > 0) {
      // create an object for the module; for example, $iothub/twin/...
      // would result in there being a message.twin object
      const mod = message[path[1]] = new MethodDescription();

      // populates the request ID if there is one
      if (query.$rid) {
        message.requestId = query.$rid;
      }

      // parse the other properties properties (excluding $rid)
      message.properties = query;
      delete message.properties.$rid;

      // save the body
      message.body = body;

      // parse the verb
      if (path.length > 2 && path[2].length > 0) {
        mod.verb = path[2];

        // This is a topic that looks like this:
        //  $iothub/methods/POST/{method name}?$rid={request id}&{serialized properties}
        // We parse the method name out.
        if (path.length > 3 && path[3].length > 0) {
          mod.methodName = path[3];
        } else {
          // The service published a message on a strange topic name. This is
          // probably a service bug. At any rate we don't know what to do with
          // this strange topic so we throw.
          throw new Error('Device method call\'s MQTT topic name does not include the method name.');
        }
      }
    }

    return message;
  }

  return undefined;
}