readAllItems and writeItems stopped when is waiting

[gustavotremont]

Hi! now i have a problem when i called the function readAllItems or writeItems, there is a part in the code that block

if (self.isWriting() || self.writeInQueue) {
      outputLog("You must wait until all previous writes have finished before scheduling another. ", 0, self.connectionID);
      return 1;  // Watch for this in your code - 1 means it hasn't actually entered into the queue.
}

//readAllItems
if (self.isWaiting()) {
      outputLog("Waiting to read for all R/W operations to complete.  Will re-trigger readAllItems in 100ms.", 0, self.connectionID);
      clearTimeout(self.rereadTimer);
      self.rereadTimer = setTimeout(function() {
	      self.rereadTimer = undefined; //already fired, can safely discard
	      self.readAllItems.apply(self, arguments);
      }, 100, arg);
      return;
}

in the logs, just show the outputlog of this two codes, and don't continue with the rest of the code, i know that because there are other logs that should show up but don't.

here my code:

exports.getPLCValues = function(s7) {
  logger.verbose('<INVOKE> controller:getPLCValues');
  /**
   * Returns the values readed from the plc or an error
   */
  return new Promise((resolve, reject) => {

    /**
     * Call the method of the nodes7 library to read the variables
     * indicated when the s7 connection started.
     */
    s7.readAllItems(function(anythingBad, values) {
      logger.debug('Reading values from PLC.');
      if (anythingBad) {
        logger.error(
          '<RETURN> controller:valuesReady Something went wrong reading values.'
        );
        const err = 'Something went wrong reading values.';
        reject(err);
      }

      logger.verbose('<RETURN> controller:getPLCValues');
      resolve(values);
    });
  });
};

exports.setPLCValues = function(variable, value, nodes7) {
  logger.verbose('<INVOKE> controller:setPLCValues Variable to write: ' +
    variable + ', value to set: ' + value);
  /**
   * Returns the values readed from the plc or an error
   */
  return new Promise((resolve, reject) => {

    /**
     * Call the method of the nodes7 library to read the variables
     * indicated when the s7 connection started.
     */
    nodes7.writeItems(variable, value, function(anythingBad) {
      logger.debug('Setting: ' + variable + ', to: ' + value);
      if (anythingBad) {
        logger.error(
          '<RETURN> controller:valuesReady Something went wrong writing values. ' + anythingBad
        );
        const err = 'Something went wrong writing values';
        reject(err);
      }

      logger.verbose('<RETURN> controller:setPLCValues');

      resolve('success');
    });
  });
};

I don't really know why this happen, and i hope anyone can help me. If you need more information please tell me. Thank!

[lylatr]

Were you able to fix this?

[MehrabHalimi84]

Hi @gustavotremont ,

I’ve been digging deep into this issue because we were facing similar ECONNRESET and timeout problems in Node-RED when sending multiple write requests rapidly.

Here is what I found (The Root Cause):

It turns out the issue isn’t just about network limits. The problem lies in how writeItems handles concurrency.

When you call writeItems while a previous write operation is still in progress, the library correctly detects the busy state and returns 1. However, it currently fails to execute the provided callback.

Because the callback never fires, the calling application (like Node-RED or any Promise-based wrapper) sits there waiting indefinitely until it eventually hits a hard timeout or disconnects.

The Fix:

I’ve patched nodeS7.js to ensure that if the library is busy, it immediately invokes the callback with a generic error (e.g., WRITE_IN_PROGRESS). This prevents the client from hanging and allows the application to handle the retry logic gracefully.

For users currently stuck:
https://github.com/MehrabHalimi84/nodeS7.git

Cheers!