title: node.js error - Can't sent headers after they are sent
body: <p>I'm using the ebay-api for node.js and when I refresh the page for some reason I get an error in the console:</p>
  
  <blockquote>
    <p>can't send headers after they are sent</p>
  </blockquote>
  
  <p>Here is my code, can anyone help me understand why I am getting the error when refreshing the page? </p>
  
  <pre><code>// example simple request to FindingService:findItemsByKeywords
  
  var ebay = require('../index.js');
  var http = require('http');
  
  var express = require('express');
  var app = express();
  var io = require('socket.io');
  
  
  app.set('port', process.env.PORT || 5000);
  
  app.get('/getEbay', function (req, res) {
      console.log('inside get');
      //  for avoiding crossbrowser-error
      res.header('Access-Control-Allow-Origin', '*');
      res.header('Access-Control-Allow-Methods', 'GET,PUT,POST,DELETE');
      res.header('Access-Control-Allow-Headers', 'Content-Type, Authorization');
      res.header('Content-Type', 'application/json');
      var params = {};
  
      params.keywords = ["cat"];
      params['paginationInput.entriesPerPage'] = 10;
      ebay.ebayApiGetRequest({
          serviceName: 'FindingService',
          opType: 'findItemsByKeywords',
          appId: 'MYAPPID',      // FILL IN YOUR OWN APP KEY, GET ONE HERE: https://publisher.ebaypartnernetwork.com/PublisherToolsAPI
          params: params,
          // filters: filters,
          parser: ebay.parseItemsFromResponse    // (default)
      },
      // gets all the items together in a merged array
    function ebayApiGetRequest(error, items) {
        if (error) throw error;
  
        console.log('Found', items.length, 'items');
        //  res.send(items);
          console.log(JSON.stringify(items));
  
  
        res.contentType('application/json');
  
        res.send(JSON.stringify(items));
  
        //  }  
    }
  );
  
  });
  
  
  http.createServer(app).listen(app.get('port'), function(){
    console.log('Express server listening on port ' + app.get('port'));
  });
  
  console.log('Listening on port 5000...');
  </code></pre>
  
  <p>I think that my mistake may be in the order for calling the functions or maybe there is a way to avoid this wrong calling?</p>