Gmail API decoding messages in Javascript

Question

I am having serious problems decoding the message body of the emails I get using the Gmail API. I want to grab the message content and put the content in a div. I am using a

Answer 1

Thank @ento 's answer. I explain more why you need to replace '-' and '_' character to '+' and '/' before decode.

Wiki Base64 Variants summary table shows:

• RFC 4648 section 4: base64 (standard): use '+' and '/'
• RFC 4648 section 5: base64url (URL-safe and filename-safe standard): use '-' and '_'

In short, Gmail API use base64url (urlsafe) format('-' and '_'), But JavaScript atob function or other JavaScript libraries use base64 (standard) format('+' and '/').

For Gmail API, the document says body use base64url format, see below links:

• string/bytes type
• MessagePartBody
• RAW

For Web atob/btoa standards, see below links:

• The algorithm used by atob() and btoa() is specified in RFC 4648, section 4
• 8.3 Base64 utility methods
• Forgiving base64