I'm working on a Firefox extension with a Node.js script as a native messaging host. Messages sent to the extension from the script are recieved as expected, but every method I have tried to listen for messages from the extension have failed.

I have tried using stdin:

process.stdin.on('readable', function() {
  let message = JSON.stringify("hello");
  sendMessage(`{"test": "${message}"}`);
});

This works fine if I run the script from the command line but it will never pick up messages sent from the extension itself.

I have also tried the npm native-messaging host protocol, based closely on the example:

var sendMessage = require('native-messaging')(handleMessage)
 
function handleMessage (req) {
    fs.writeFile('test.txt', req.message, err => {
    if (err) {
        console.error(err);
    }
    // file written successfully
    }); 
    sendMessage({message: "pong", body: 'hello from nodejs app'});
}

This also yields no result.

I have tested both methods and neither of these functions seem to ever be called, no matter how many times I send a message from the extension, and no errors are thrown.

I don't believe this is a problem with the manifest or the registry keys, because messaging seems to work fine one way.

Why are my messages not being received by the script?

Native Messaging documentation by MDN

npm Native Messaging