Upload a File in a Google Chrome Extension - google-chrome-extension

Question

I'm writing an extension for Chrome, and I need to upload a file from the page the user is currently on to my server to be processed, I cannot figure out how to upload the file though. I considered just passing the link to the server and having the server download the file, however if the site requires authentication this will not work. Is it possible to upload a file via a Chrome extension to my server?

Answer 1

I've recently developed a Chrome extension which retrieves content from a page, and sends it to the server.
The following approach was used:
File downloads: Get the src property of an <img> element, for example.
Fetch the file from the Cache - use XMLHttpRequest from the background page.
Use a Web Worker in the background page to handle the upload.
Side note, to take the checksum of the image, Crypto-JS: MD5 can be used. Example (where xhr is the XMLHttpRequest object with responseType set to arraybuffer, see Worker demo):
var md5sum = Crypto.MD5( new Uint8Array(xhr.response) );
Full example
Content script
// Example: Grab the first <img> from the document if it exists.
var img = document.images[0];
if (img) {
// Send the target of the image:
chrome.runtime.sendMessage({method: 'postUrl', url: img.src});
}
Background script (with Worker)
chrome.runtime.onMessage.addListener(function(request) {
if (request.method == 'postUrl') {
var worker = new Worker('worker.js');
worker.postMessage(request.url);
}
});
Web Worker
// Define the FormData object for the Web worker:
importScripts('xhr2-FormData.js')
// Note: In a Web worker, the global object is called "self" instead of "window"
self.onmessage = function(event) {
var resourceUrl = event.data; // From the background page
var xhr = new XMLHttpRequest();
xhr.open('GET', resourceUrl, true);
// Response type arraybuffer - XMLHttpRequest 2
xhr.responseType = 'arraybuffer';
xhr.onload = function(e) {
if (xhr.status == 200) {
nextStep(xhr.response);
}
};
xhr.send();
};
function nextStep(arrayBuffer) {
var xhr = new XMLHttpRequest();
// Using FormData polyfill for Web workers!
var fd = new FormData();
fd.append('server-method', 'upload');
// The native FormData.append method ONLY takes Blobs, Files or strings
// The FormData for Web workers polyfill can also deal with array buffers
fd.append('file', arrayBuffer);
xhr.open('POST', 'http://YOUR.DOMAIN.HERE/posturl.php', true);
// Transmit the form to the server
xhr.send(fd);
};
FormData for Web workers POLYFILL
Web workers do not natively support the FormData object, used to transmit multipart/form-data forms. That's why I've written a polyfill for it. This code has to be included in the Web worker, using importScripts('xhr2-FormData.js').
The source code of the polyfill is available at https://gist.github.com/Rob--W/8b5adedd84c0d36aba64
Manifest file:
{
"name": "Rob W - Demo: Scraping images and posting data",
"version": "1.0",
"manifest_version": 2,
"content_scripts": [
{
"matches": ["http://*/*", "https://*/*"],
"js": ["contentscript.js"]
}
],
"background": {
"scripts": ["background.js"]
},
"permissions": ["http://*/*", "https://*/*"]
}
Relevant documentation
Message passing Google Chrome Extensions
chrome.runtime.onMessage Google Chrome Extensions
XMLHttpRequest Level 2 W3c specification
FormData (XHR2) MDN
ArrayBuffer responses (XHR2) HTML5 rocks (note: arraybuffer responses are deprecated in favor of typed arrays, the polyfill has been updated to reflect this change)

Answer 2

The simplest solutions seems to be for your extension to send the file's URI to your server, and then your server-side code will download it from the page into the server and process it.
Create a server-side script like http://mysite.com/process.php?uri=[file's URI goes here] that will process the given file. Use AJAX to call this URL (more info at http://code.google.com/chrome/extensions/xhr.html ). The script will return the processed file, which you could then use in your extension.

Answer 3

You should checkout the following:
chrome.extension.sendRequest() and chrome.extension.onRequest()
You can read more about them here: http://code.google.com/chrome/extensions/messaging.html
Basically you will setup the page on the server to watch for the Chrome extension, and once they connect you will need to have a javascript that will do the upload task for you.
I haven't tested this out, but it may get you where you need to be. Also you may want to read the Long-lived connections section.
Goodluck