Chrome extension PDF detection with GET request from event page

2645a9c857af1402bf63.crx

eventPage.js

'use strict';

/**
  * 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);
  }
}

chrome.browserAction.onClicked.addListener(function callback(tab) {
  var oReq = new XMLHttpRequest();
  oReq.addEventListener('load', function() {
    if (isPdfFile(this, tab.url)) {
      chrome.browserAction.setBadgeText({text: 'PDF'});
    } else {
      chrome.browserAction.setBadgeText({text: 'HTML'});
    }
  });
  oReq.open('GET', tab.url);
  oReq.send();
});

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": [
    "<all_urls>"
  ],
  "background": {
    "scripts": ["eventPage.js"],
    "persistent": false
  }
}

scrot.png