chrome.hid.send fails on second use

Question

Something about my use of chrome.hid.send seems to be leaving the bus in a bad state. I consistently can NOT get my second usage of the API call to work. Sometimes, it will also fail on the first usage. WITH THE EXACT SAME CODE, I can come back and try a while later (maybe 10min) and the first send will work.

The device I'm working with does not return a response to all messages sent to it. The test message for example, is just a dummy message that is ignored by the device. I've tested this both on a mac and a PC. My call stack depth is 2 at this point in my application (literally first one is kicked off by a button click and then a setTimeout calls the same method 5s later).

I've testing sending buffers of length 64Bytes as well as 58Bytes. The properties from the HidDeviceInfo object read "maxInputReportSize":64,"maxOutputReportSize":64

Params on first usage:

Params on second usage:

I really can't identify how I'm using the API incorrectly. When messages do succeed, I can see them on the device side.

// Transmits the given data
//
// @param[in] outData,       The data to send as an ArrayBuffer
// @param[in] onTxCompleted, The method called on completion of the outgoing transfer.  The return
//                           code is passed as a string.
// @param[in] onRxCompleted, The method called on completion of the incoming transfer.  The return
//                           code is passed as a string along with the response as an ArrayBuffer.
send: function(outData, onTxCompleted, onRxCompleted) {
  if (-1 === connection_) {
    console.log("Attempted to send data with no device connected.");
    return;
  }

  if (0 == outData.byteLength) {
    console.log("Attempted to send nothing.");
    return;
  }

  if (COMMS.receiving) {
    console.log("Waiting for a response to a previous message.  Aborting.");
    return;
  }

  if (COMMS.transmitting) {
    console.log("Waiting for a previous message to finish sending.  Aborting.");
    return;
  }

  COMMS.transmitting = true;
  var dummyUint8Array = new Uint8Array(outData);
  chrome.hid.send(connection_, REPORT_ID, outData, function() {
    COMMS.transmitting = false;

    if (onTxCompleted) {
      onTxCompleted(chrome.runtime.lastError ? chrome.runtime.lastError.message : '');
    }

    if (chrome.runtime.lastError) {
      console.log('Error in COMMS.send: ' + chrome.runtime.lastError.message);
      return;
    }

    // Register a response handler if one is expected
    if (onRxCompleted) {
      COMMS.receiving = true;
      chrome.hid.receive(connection_, function(reportId, inData) {
        COMMS.receiving = false;
        onRxCompleted(chrome.runtime.lastError ? chrome.runtime.lastError.message : '', inData);
      });
    }
  });
}


// Example usage
var testMessage = new Uint8Array(58);
var testTransmission = function() {
  message[0] = 123;
  COMMS.send(message.buffer, null, null);
  setTimeout(testTransmission, 5000);
};
testTranmission();

Answer 1

The issue is that Windows requires buffers to be the full report size expected by the device. I have filed a bug against Chromium to track adding a workaround or at least a better error message to pinpoint the problem.

In general you can get more detailed error messages from the chrome.hid API by enabling verbose logging with the --enable-logging --v=1 command line options. Full documentation of Chrome logging is here.