Send mail with attachment (PDF) using Gmail API

Question

Problem

All the data is sent in text format rather than as PDF as an attachment.

My Code

var boundary = "__myapp__", nl = "\n";
// var attach = data.toString("base64");
var fileName = "abc.pdf";
var attach = new Buffer(fs.readFileSync("./" + fileName)).toString("base64");

var str = ["Content-Type: text/plain; charset=\"UTF-8\"\n",
    "MIME-Version: 1.0\n",
    "Content-Transfer-Encoding: 7bit\n",
    "to: ", to, "\n",
    "subject: ", subject, "\n\n",
    "Content-Type: multipart/alternate; boundary=" + boundary + nl,
    "--" + boundary,
    "Content-Type: text/plain; charset=UTF-8",
    "Content-Transfer-Encoding: 7bit" + nl,
    message + nl,
    "--" + boundary,
    "--" + boundary,
    "Content-Type: Application/pdf; name=myPdf.pdf",
    'Content-Disposition: attachment; filename=myPdf.pdf',
    "Content-Transfer-Encoding: base64" + nl,
    attach,
    "--" + boundary + "--"
].join('');

var encodedMail = new Buffer(str).toString("base64")
    .replace(/\+/g, '-')
    .replace(/\//g, '_');

resolve(encodedMail);

A part of mail is as below

Content-Type: multipart/alternate; boundary=myapp --_myapp_Content-Type: text/plain; charset=UTF-8Content-Transfer-Encoding: 7bit test message --myapp--_myapp_Content-Type: Application/pdf; name=myPdf.pdfContent-Disposition: attachment; filename=myPdf.pdfContent-Transfer-Encoding: base64 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...more texts...at last...==--myapp--

What I think is that there might be some issue with the template of sending the mail with attachment.

Can anyone provide help here?
Thanks

Answer 1

I was able to attach a PDF file by using a proper message structure. It's really important to set the correct mimeTypes and the boundaries.

This reference (https://stackoverflow.com/a/50540373/13664358) pointed out by @Tanaike helped a lot!

Here is the whole function to send an email with a PDF attachment:

const subject = 'My Subject';
const utf8Subject = `=?utf-8?B?${Buffer.from(subject).toString('base64')}?=`;

var fileName = "mypdf.pdf";
var attach = new Buffer.from(fs.readFileSync("./" + fileName)).toString("base64");

var emailBody = 'My Email Message';

var messageParts = [
    "MIME-Version: 1.0",
    'From: Teste <[email protected]>',
    'To: Teste <[email protected]>',
    `Subject: ${utf8Subject}`,
    "Content-Type: multipart/mixed; boundary=012boundary01",
    '',
    "--012boundary01",
    "Content-Type: multipart/alternative; boundary=012boundary02",
    '',
    "--012boundary02",
    "Content-type: text/html; charset=UTF-8", 
    "Content-Transfer-Encoding: quoted-printable",
    '',
    emailBody,
    '',
    "--012boundary02--",
    "--012boundary01",
    "Content-Type: Application/pdf; name=mypdf.pdf",
    'Content-Disposition: attachment; filename=mypdf.pdf',
    "Content-Transfer-Encoding: base64",
    '',
    attach,
    "--012boundary01--",
]

const message = messageParts.join('\n');

// The body needs to be base64url encoded.
const encodedMessage = Buffer.from(message)
  .toString('base64')
  .replace(/\+/g, '-')
  .replace(/\//g, '_')
  .replace(/=+$/, '');

const gmail = google.gmail({version: 'v1', auth});
gmail.users.messages.send({
  userId: 'me',
  requestBody: {
      raw: encodedMessage
  }
}, (err, res) => {
  if (err) return console.log('The API returned an error: ' + err);
});

Note: The code above uses google apis for nodejs (https://www.npmjs.com/package/googleapis)

For multiples PDFs, we can add them between --012boundary02-- and --012boundary01-- as follows:

"--012boundary02",
"Content-type: text/html; charset=UTF-8", 
"Content-Transfer-Encoding: quoted-printable",
'',
emailBody,
'',
"--012boundary02--",
"--012boundary01",
"Content-Type: Application/pdf; name=mypdf.pdf",
'Content-Disposition: attachment; filename=mypdf.pdf',
"Content-Transfer-Encoding: base64",
'',
attach,
"--012boundary01",
"Content-Type: Application/pdf; name=mypdf2.pdf",
'Content-Disposition: attachment; filename=mypdf2.pdf',
"Content-Transfer-Encoding: base64",
'',
attach2,
"--012boundary01",
"Content-Type: Application/pdf; name=mypdf3.pdf",
'Content-Disposition: attachment; filename=mypdf3.pdf',
"Content-Transfer-Encoding: base64",
'',
attach3,
"--012boundary01--",