Using python 3 and Gmail API to send emails with attachments, I end up with either corrupted files or ConnectionAbortedError

Question

I am using the Gmail API in Python 3 to send emails with attachments, based on their example code

I've got the following to create the message:

def create_message_with_attachment(
    sender, to, subject, message_text, files):
  """Create a message for an email.

  Args:
    sender: Email address of the sender.
    to: Email address of the receiver.
    subject: The subject of the email message.
    message_text: The text of the email message.
    file: The path to the file to be attached.

  Returns:
    An object containing a base64url encoded email object.
  """
  message = MIMEMultipart()
  message['to'] = to
  message['from'] = sender
  message['subject'] = subject

  msg = MIMEText(message_text)
  message.attach(msg)

  for file in files:

    content_type, encoding = mimetypes.guess_type(file)

    if content_type is None or encoding is not None:
      content_type = 'application/octet-stream'
    main_type, sub_type = content_type.split('/', 1)
    if main_type == 'text':
      fp = open(file, 'rb')
      msg = MIMEText(fp.read(), _subtype=sub_type)
      fp.close()
    elif main_type == 'image':
      fp = open(file, 'rb')
      msg = MIMEImage(fp.read(), _subtype=sub_type)
      fp.close()
    elif main_type == 'audio':
      fp = open(file, 'rb')
      msg = MIMEAudio(fp.read(), _subtype=sub_type)
      fp.close()
    else:
      fp = open(file, 'rb')
      msg = MIMEBase(main_type, sub_type)
      msg.set_payload(fp.read())
      fp.close()
    filename = os.path.basename(file)
    msg.add_header('Content-Disposition', 'attachment', filename=filename)
    message.attach(msg)

  raw = base64.urlsafe_b64encode(message.as_bytes())
  raw = raw.decode()
  body = {'raw': raw}
  return body

And the following to send:

def send_message(service, user_id, message):
    """Send an email message.

  Args:
    service: Authorized Gmail API service instance.
    user_id: User's email address. The special value "me"
    can be used to indicate the authenticated user.
    message: Message to be sent.

  Returns:
    Sent Message.
    """
    try:
        message = (service.users().messages().send(userId=user_id, body=message).execute())
        print ('Sent! Message Id: %s' % message['id'])
        return message
    except httplib2.HttpLib2Error as error:
        return None
        print ('An error occurred: %s' % error)

When I send a mail created like this (I need to send pdf's, but tried with a zip as well with the same results) it works but the files are corrupted. I'm assuming this happens during the base64 encoding.

I saw in another post that adding encoders.encode_base64(msg) (just above/below filename = os.path.basename(file) in my case) solves the issue, however when I add that line I get: ConnectionAbortedError: [WinError 10053] An established connection was aborted by the software in your host machine

Apparently it does that when it doesn't like a file?

Any idea what I'm doing wrong?

Answer 1

The confusion with the correct encoding is due to the change from Python 2 to Python 3

The encoding procedure described in the Google documentation for sending emails is based on Python 2. I assume you are using Python 3.

To adapt the guide to the new Python version two modifications need to be implemented.

1. Modify return {'raw': base64.urlsafe_b64encode(message.as_string())} to return {'raw': base64.urlsafe_b64encode(message.as_bytes()).decode()}. You have done this already.
2. After msg.set_payload(contents) request you need to add an additional line encoders.encode_base64(msg). This is what you were missing.

Now that you added it, mind that encoders is a module of the package email. If not already done, you need to add to your code from email import encoders