Google App Engine - Error uploading file to blobstore from Python code

Question

I am working on an app to process emails hitting my mailbox. I have modified my mail settings to forward incoming mails to myapp. The mails reaching myapp will be routed to the handler script ("handle_incoming_email.py") where it will be processed. My app.yaml file looks like this

app.yaml

application: myapp
version: 1-1
runtime: python27
api_version: 1
threadsafe: false
default_expiration: "360d"

handlers:
- url: /_ah/mail/.+
  script: myapp/utils/handle_incoming_email.py

The mail handler script is given below

handle_incoming_email.py

import logging
import urllib
import base64
import traceback
from google.appengine.ext import webapp
from google.appengine.ext import blobstore
from google.appengine.api import urlfetch
from google.appengine.ext.webapp.util import run_wsgi_app
from google.appengine.ext.webapp.mail_handlers import InboundMailHandler


class ReceiveEmail(InboundMailHandler):

    def receive(self, message):
        try:
            for filename, filecontents in message.attachments:
                if filecontents.encoding:
                    # data = filecontents
                    data = filecontents.decode()
                    # data = filecontents.payload
                    # data = filecontents.payload.decode()
                    # data = base64.b64decode(filecontents.decode())
                    # data = base64.b64decode(filecontents.payload)
                    # data = base64.b64decode(filecontents.payload.decode())

                upload_url = blobstore.create_upload_url('http://myapp.appspot.com/settings/saveItem/')
                form_fields = {'field_name': data}
                form_data = urllib.urlencode(form_fields)
                result = urlfetch.fetch(url=upload_url,
                                        payload=form_data,
                                        method=urlfetch.POST,
                                        headers={'Content-Type': 'application/x-www-form-urlencoded'})
                logging.info(result)
        except Exception, e:
            traceback.print_exc()

application = webapp.WSGIApplication([ReceiveEmail.mapping()], debug=True)


def main():
    run_wsgi_app(application)
if __name__ == "__main__":
    main()

My requirement is to create an entity corresponding to each mail with attachment. For this, I need to parse the attachment from the mail and upload it to blobstore. However, when I try to upload the attachment to blobstore, I get the following error:

The request's content type is not accepted on this URL.

As you can see in the commented code in "handle_incoming_email.py", I tried different methods (trial-and-error) to get the data correct, but to no avail.

Could someone guide me in fixing this!

Thanks!!!

Answer 1

I think this code sample will solve you problem. You probably need to use only encode_multipart_formdata function from this code. And do not forget to set properly content type.

class BlobstoreUpload(blobstore_handlers.BlobstoreUploadHandler):
  def post(self):
    upload_files = self.get_uploads('file')
    blob_info = upload_files[0]
    return self.response.write(blob_info.key())

  @classmethod
  def encode_multipart_formdata(cls, fields, files, mimetype='image/png'):
    """
    Args:
      fields: A sequence of (name, value) elements for regular form fields.
      files: A sequence of (name, filename, value) elements for data to be
        uploaded as files.

    Returns:
      A sequence of (content_type, body) ready for urlfetch.
    """
    boundary = 'paLp12Buasdasd40tcxAp97curasdaSt40bqweastfarcUNIQUE_STRING'
    crlf = '\r\n'
    line = []
    for (key, value) in fields:
      line.append('--' + boundary)
      line.append('Content-Disposition: form-data; name="%s"' % key)
      line.append('')
      line.append(value)
    for (key, filename, value) in files:
      line.append('--' + boundary)
      line.append('Content-Disposition: form-data; name="%s"; filename="%s"' % (key, filename))
      line.append('Content-Type: %s' % mimetype)
      line.append('')
      line.append(value)
    line.append('--%s--' % boundary)
    line.append('')
    body = crlf.join(line)
    content_type = 'multipart/form-data; boundary=%s' % boundary
    return content_type, body


class UserProfile(webapp2.RequestHandler):
  def post(self):
    picture = self.request.POST.get('picture')

    # Write new picture to blob
    content_type, body = BlobstoreUpload.encode_multipart_formdata(
      [], [('file', name, image)])
    response = urlfetch.fetch(
      url=blobstore.create_upload_url(self.uri_for('blobstore-upload')),
      payload=body,
      method=urlfetch.POST,
      headers={'Content-Type': content_type},
      deadline=30
    )
    blob_key = response.content