Gmail returns base64 encoded but lists as quotable printable

Question

When I call the Gmail API I get the following back (just an excerpt obviously since the body is massive:

{
  ...
  payload: {
    ...
    parts: [
      {
        "partId": "1",
        "mimeType": "text/html",
        "filename": "",
        "headers": [
         {
          "name": "Content-Type",
          "value": "text/html; charset=\"UTF-8\""
         },
         {
          "name": "Content-Transfer-Encoding",
          "value": "quoted-printable"
         }
        ],
        "body": {
             "size": 4696,
             "data": "PCFET0NUWVBFIGh0bWw-PGh0bWwgbGFuZz1lbj48....

I have just included the relevant parts. You will see that the html body part has the email encoded as base64Url, but toe content transfer encoding clearly says quoted-printable. I run it through a base64url decoder and it gives the correct data. But the header explicitly says it is quoted-printable

What am I missing?

The plain body part is this, which seems perfectly correct.

"headers": [
 ...
{
 "name": "Content-Transfer-Encoding",
 "value": "base64"
}   ],
"body": {
 "size": 601,
 "data": "R29vZ2xlIEFQSXMgRXhwbG9yZXIgd2FzIGdyYW5

Answer 1

When you request a Message resource, the Gmail API can deliver message data in one of four formats that you can set via a query string (see documentation).

Below is a description of each format option, taken from the official docs:

• "full": Returns the full email message data with body content parsed in the payload field; the raw field is not used. (default)
• "metadata": Returns only email message ID, labels, and email headers.
• "minimal": Returns only email message ID and labels; does not return the email headers, body, or payload.
• "raw": Returns the full email message data with body content in the raw field as a base64url encoded string; the payload field is not used.

"full" is the default option where the body content is parsed and automatically stored as a base64 encoded string in the data property.

Keep in mind that the Message resource object is provided as a convenience to interact with the RFC5322 payload and it always provides its data payload in base64 regardless of the value on the Content-Transfer-Encoding header.

If you want to wrangle with the raw IMF(Internet Message Format - RFC5322) text, then set the format to "raw" in your query string. You'll have to base64 decode the raw string to get the IMF data. It will look exactly as you expect, but you'll have to write your own parser to manage its contents.