How to save HTML5 canvas image to Google App Engine

imgsaver.py

import re
import base64
# ...
class SaveHandler(webapp.RequestHandler):
  dataUrlPattern = re.compile('data:image/(png|jpeg);base64,(.*)$')
  
  def post(self):
    # ...
    imgdata = self.request.get('imgdata')
    imgb64 = self.dataUrlPattern.match(imgdata).group(2)
    if imgb64 is not None and len(imgb64) > 0:
      datamodel.image = db.Blob(base64.b64decode(imgb64))

imguploader.js

// The client side code sends the canvas's content via 
// a jQuery post method to server

params = { imgdata : canvas.toDataURL('image/jpeg') };
$.post('/save', params, function (data) { /* ... */ })

//...