create_application.js

var net      = require('net');
var fs       = require('fs');
var os       = require('os');
var path     = require('path');
var osExtras = require('./os_extras');

let defaultOptions = {
  name: 'Application',
  socketPath: 'application'
};

function getDefaultSocket() {
  let pipeName = `application-${process.env.USER}-sock`;
  let tmpName  = `application-${process.env.USER}.sock`;
  return osExtras.isWindows() ? `\\\\.\\pipe\\${pipeName}` : path.join(os.tmpdir(), tmpName);
}

function deleteSocketFile(socketPath) {
  // no need to delete the socket file on windows, pipes are cleaned up
  if ( osExtras.isWindows() ) { return; }

  if ( fs.existsSync(socketPath) ) {
    try {
      fs.unlinkSync(socketPath);
    } catch (error) {
      // Ignore ENOENT errors in case the file was deleted between the exists
      // check and the call to unlink sync.
      if (error.code != 'ENOENT') {
        // rethrow the error
        throw error;
      }
    }
  }
}

// Create server to listen for additional application launches
function listenForNewProcesses(socketPath) {
  // delete any current socket paths
  deleteSocketFile(socketPath);

  // create a server for listening on the socket path
  var server = net.createServer(function(connection) {
    connection.on('data', function(data) {
      console.log('Another instance of the application was launched and will terminate');
    });
  });

  // listen on the socket path to allow other instance to know to terminate
  server.listen(socketPath);

  // log errors
  server.on('error', function(error) {
    console.error('Application server failed', error);
  });
}

class Application {
  constructor(options = {}) {
    // listen for new processes to connect so they can know
    // to terminate themselves because an instance is already running
    listenForNewProcesses(options.socketPath);
  }

  getName() {
    return this.name;
  }
}

export default (options = {}) => {
  options = Object.assign({}, defaultOptions, options);
  var app = require('app');

  // application callback
  function createApplication() {
    return new Application(options);
  }

  // if the socket doesn't exist or the platform is windows
  // attempt to connect to determine if another instance is running
  if ( osExtras.isWindows() || fs.existsSync(socketPath) ) {
    // attempt to connect on the socket path and if we can
    // terminate the application, an instance is already running
    var client = net.connect({ path: socketPath }, function(){
      // write to the socket and terminate
      client.write('{}', function() {
        client.end();
        app.terminate();
      });
    });
    // continue with application startup if the client errors
    client.on('error', createApplication);
  }
};