app.yaml

application: to-data-uri
version: 0
runtime: python
api_version: 1

handlers:
- url: /.*
  script: handler.py

gistfile3.txt

handler.py

from google.appengine.ext.webapp import WSGIApplication, RequestHandler
from google.appengine.ext.webapp.util import run_wsgi_app
from google.appengine.api.urlfetch import fetch
from base64 import b64encode
import re

def json_literal_escape(str):
    retval = ""
    for c in str:
        c = ord(c)
        if c == 34:
            retval += "\\\""
        elif c == 92:
            retval += "\\\\"
        elif c == 8:
            retval += "\\b";
        elif c == 9:
            retval += "\\t";
        elif c == 10:
            retval += "\\n";
        elif c == 11:
            retval += "\\v";
        elif c == 12:
            retval += "\\f";
        elif c == 13:
            retval += "\\r";
        elif c < 32:
            retval += "\\u%04x" % c;
        else:
            retval += unichr(c)
    return retval

def extract_mime_type(ct_header):
    return re.sub("\s*;.*", "", ct_header)

class Default(RequestHandler):
    def get(self):
        url = self.request.get("url")
        callback = self.request.get("callback")
        try:
            if callback == "":
                raise Exception("callback is not given")
            data = fetch(url, follow_redirects=True, deadline=2)
            self.response.headers["Content-Type"] = "text/javascript"
            self.response.out.write(u"%s({\"result\":\"%s\"})" % (
                callback,
                json_literal_escape(
                    u"data:%s;base64,%s" % (
                        extract_mime_type(data.headers["Content-Type"]),
                                         b64encode(data.content)))))
        except Exception, e:
            self.response.set_status(500)
            self.response.headers["Content-Type"] = "text/plain"
            self.response.out.write(u"error: " + str(e))


if __name__ == "__main__":
    run_wsgi_app(WSGIApplication([("/", Default)]))