What is the encoding of the body of Gmail message? How to decode it?

This is base64.

Your truncated message is:

---------- Forwarded message ----------
From: LinkedIn <[email protected]>
Date: Sat, Sep 3, 2016 at 9:30 AM
Subject: Application for Senior Backend Develop

Here's some sample code:

I had to remove the last 3 characters from your truncated message because I was getting the same padding error as you. You probably have some garbage the message you're trying to decode.

import base64

body = "LS0tLS0tLS0tLSBGb3J3YXJkZWQgbWVzc2FnZSAtLS0tLS0tLS0tDQpGcm9tOiBMaW5rZWRJbiA8am9iLWFwcHNAbGlua2VkaW4uY29tPg0KRGF0ZTogU2F0LCBTZXAgMywgMjAxNiBhdCA5OjMwIEFNDQpTdWJqZWN0OiBBcHBsaWNhdGlvbiBmb3IgU2VuaW9yIEJhY2tlbmQgRGV2ZWxv"

result = base64.b64decode(body)

print(result)

UPDATE

Here's a snippet for gettting and decoding the message body. The decoding part was taken from the gMail API documentation:

  message = service.users().messages().get(userId='me', id=msg_id, format='full').execute()
  msg_str = base64.urlsafe_b64decode(message['payload']['body']['data'].encode('UTF8'))
  mime_msg = email.message_from_string(msg_str) 

  print(msg_str)

Reference doc: https://developers.google.com/gmail/api/v1/reference/users/messages/get#python

Important distinction, it is web safe base64 encoded (aka "base64url") . The docs are not very good on it, the MessagePartBody is best documented here: https://developers.google.com/gmail/api/v1/reference/users/messages/attachments

And it says the type is "bytes" (which obviously isn't save to transmit over JSON as-is), but I agree with you, it doesn't clearly specify it's base64url encoded like other "bytes" fields are in the API.

As for padding issues, is it because you're truncating? If not, check that "len(data) % 4 == 0", if not, it means the API is returning unpadded data, which would be unexpected.

It's base64. You can use base64.decodestring to read it. The part of the message that your attached is: '---------- Forwarded message ----------\r\nFrom: LinkedIn <[email protected]>\r\nDate: Sat, Sep 3, 2016 at 9:30 AM\r\nSubject: Application for Senior Backend Develo'

The incorrect padding error means that you're decoding an incorrect number of characters. You're probably trying to decode a truncated message.