Chrome extension PDF detection with GET request from content script

27bdaa36aca3b6d6ffa9.crx

contentScript.js

/**
  * Check if the request is a PDF file.
  * @param {Object} details First argument of the webRequest.onHeadersReceived
  *                         event. The properties "responseHeaders" and "url"
  *                         are read.
  * @return {boolean} True if the resource is a PDF file.
  */
function isPdfFile(response, url) {
  var header = response.getResponseHeader('content-type');
  if (header) {
    var headerValue = header.toLowerCase().split(';', 1)[0].trim();
    return (headerValue === 'application/pdf' ||
            headerValue === 'application/octet-stream' &&
            url.toLowerCase().indexOf('.pdf') > 0);
  }
}

var oReq = new XMLHttpRequest();
var url = window.location.toString();
oReq.addEventListener('load', function() {
  if (isPdfFile(this, url)) {
    chrome.runtime.sendMessage({type: 'PDF'});
  } else {
    chrome.runtime.sendMessage({type: 'HTML'});
  }
});
oReq.open('GET', url);
oReq.send()

eventPage.js

'use strict';

chrome.runtime.onMessage.addListener(
  function(request, sender, sendResponse) {
    chrome.browserAction.setBadgeText({text: request.type});
});

manifest.json

{
  "manifest_version": 2,
  "name": "Detecting PDFs with GET requests Demo",
  "description": "This extension demonstrates a technique for detecting PDFs GET requests",
  "version": "1.0",
  "browser_action": {},
  "permissions": [
  ],
  "background": {
    "scripts": ["eventPage.js"],
    "persistent": false
  },
  "content_scripts": [
    {
      "matches": ["<all_urls>"],
      "js": ["contentScript.js"]
    }
  ]
}

scrot.png