CODEWITHSUNDEEP
serial-portgoogle-chrome-app
Gordon Williams
Gordon Williams

Reputation: 1886

Detecting Serial port disconnect in Chrome App

I'm using Chrome's Serial Port API (http://developer.chrome.com/apps/serial.html) in a Web App.

The problem I have is that pretty much all serial ports now are implemented via USB devices. If the user disconnects (or just resets) the USB device, I don't have any way of knowing. Not only that, because the app hasn't disconnected in Chrome (because it didn't know), if the USB device is plugged back in, bad things happen (on Linux it just gets a different name, but in Windows it is not usable at all).

The best I can manage is:

  var checkConnection = function() {
    chrome.serial.getControlSignals(connectionInfo.connectionId, function (sigs) { 
      var connected = "cts" in sigs;
      if (!connected) console.log("Disconnected");
   });
  } // called every second or so

Is there a better way? a callback would be ideal!

Upvotes: 4

Views: 1830

Answers (1)

kqnr
kqnr

Reputation: 3596

It looks it should be safe on all platforms to assume that getting a read callback with 0 bytes means EOF, which in turn is a good indication that the device has been disconnected.

chrome.serial.read(connectionId, function(readInfo) {
    if (readInfo.bytesRead === 0) {
        /// Safely assume the device is gone. Clean up.
        chrome.serial.close(connectionId);
        /// ...
    }
});

The serial API will be improving over the next few weeks (in Canary at least) to add stability improvements, an event-based read API, and the ability to more clearly detect timeouts and error conditions (like a disconnected device). You can track that progress at http://crbug.com/307184.

Upvotes: 4

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