Google API Service Account Demo for Gmail and Drive

app.js

//
// Using Google Drive and Google Mail with a Service Account.
//
// Amswer to http://stackoverflow.com/questions/37902022/gmail-api-with-nodejs-send-gives-400-bad-request?answertab=active#tab-top
//
// A service account is pretty much like a normal Google account, except that yo can't get get a "shell" like
// the Gmail webapp or Drive webapp into it. To manage email with a Service Account, the administrator for the 
// domain which owns the email addresses must enable API access for the Service Account. That's described in my
// SO post and the links therein.  Assuming you've set all that up, it's time to have some fun!
//
// This gist was significantly inspired by examples distributed by Google under the Apache License 2 and is returned to
// the community also under the Apache License 2. 

var fs = require('fs');
var base64 = require('base64-url');  // for encoding our email

// service account key - keep it safe
var key = require('./serviceaccount_key.json');

// google apis
var google = require('googleapis');
var drive = google.drive('v3');
var mail = google.gmail('v1');

// new up a client - include whatever scopes you need
var jwtClient = new google.auth.JWT(
	key.client_email, 
	null, 
	key.private_key, 
	['https://www.googleapis.com/auth/drive', 		// drive scope
	'https://www.googleapis.com/auth/gmail.readonly',	// for labels
	'https://www.googleapis.com/auth/gmail.send'], 		// mail scope
	"maria@our_google_apps_domain.com");			// the user which wil be impersonated by our service account

// grab some tokens; we won't have to get our hands dirty because its's all nicely encapsulated in the jwtClient
jwtClient.authorize(function(err, tokens) {
	if (err) {
		console.log('JWT Auth Error: ' + err);
		return;
	}

        // Let's have a look just for funsies!
	console.log('Got tokens:' + JSON.stringify(tokens));

        // Find out what our friend Maria has in her Google Drive
	listFiles();
        // Leave a present for her!
	console.log('pushing file...');
	var request = putFile('test.png');	// not much of a present...
	console.log(JSON.stringify(request));	// hey check out that HTTPS request!

	// What labels is Maria using in Gmail?
	request = mail.users.labels.list({auth: jwtClient, userId: 'me'},
		(err,res) => {
			if (err) console.log('Labels Error:\n' + JSON.stringify(err));
			if (res) console.log('Labels:\n' + JSON.stringify(res));
		}
	);


	// now we're going to send an email from Maria to Manny.
	var msg = [
		'Content-Type: text/plain; charset=utf-8\n',
		'MIME-Version: 1.0\n',
		'Content-Transfer-Encoding: 7bit\n',
		'To: manny@example.com\n',		     // who's this Danny guy, and why is Maria sending him email?
		'From: maria@our_google_apps_domain.com\n',  // better match the impersonated account
		'Subject: Happy Hour\n\n',
		'See you at happy hour!'
		].join('');

	console.log(msg);
	safe = base64.escape(base64.encode(msg));
	console.log(safe);

	request = mail.users.messages.send(
		{
			auth: jwtClient,
			userId: 'me',		// this refers to the service avvount
			resource: 
			{
				raw: safe
			}
		},
		(err,resp)=>{
			console.log('error:\n' + JSON.stringify(err));
			console.log('response:\n' + JSON.stringify(resp));
			}
	);
	console.log(JSON.stringify(request));

});


// Make an authorized request to list Drive files.
function listFiles() {  
	drive.files.list({ auth: jwtClient, pageSize: 10, fields: "nextPageToken, files(id, name)" }, 
		function(err, resp) {
		    // handle err and response
		    if (err) {
		      console.log('FAIL: ', err);
		    } else {
		      var files = resp.files;
		      if (files.length == 0)
			console.log('no files found');
		      else {
			console.log('Files:');
			for (var i=0; i<files.length;i++) {
			  var file = files[i];
			  console.log('%s (%s)', file.name, file.id);
			}
		      }
		    }
	  	});
};


function putFile(filename) {
	var req = drive.files.create({
		auth: jwtClient,
		resource: {
			name: 'testimage.png',
			mimeType: 'image/png'
		},
		media: {
			mimeType: 'image/png',
			body: fs.createReadStream(filename)
		}
	}, ()=> {
			console.log('drive.files.create callback here!');
			listFiles();
		} );

	return req;
};

This answers how to get a Service Account to work with Gmail plus some fun with Google Drive.