fix(Gmail Node): Do not break threads while creating drafts (#16272)

Co-authored-by: Shireen Missi <94372015+ShireenMissi@users.noreply.github.com>
Co-authored-by: cubic-dev-ai[bot] <191113872+cubic-dev-ai[bot]@users.noreply.github.com>

packages/nodes-base/nodes/Google/Gmail/GenericFunctions.ts

@@ -250,7 +250,7 @@ export async function encodeEmail(email: IEmail) {
 
 	const mailBody = await mail.build();
 
-	return mailBody.toString('base64').replace(/\+/g, '-').replace(/\//g, '_');
+	return mailBody.toString('base64').replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/, '');
 }
 
 export async function googleApiRequestAllItems(

packages/nodes-base/nodes/Google/Gmail/test/v2/GmailV2.node.test.ts

@@ -193,6 +193,15 @@ describe('Test Gmail Node v2', () => {
 				.query({ userId: 'me', uploadType: 'media' })
 				.reply(200, messages[0]);
 			gmailNock.delete('/v1/users/me/drafts/test-draft-id').reply(200, messages[0]);
+			gmailNock
+				.get('/v1/users/me/threads/test-thread-id')
+				.query({
+					format: 'metadata',
+					metadataHeaders: 'Message-ID',
+				})
+				.reply(200, {
+					messages: [{ payload: { headers: ['jjkjkjkf@reply.com'] } }],
+				});
 			gmailNock
 				.get('/v1/users/me/drafts/test-draft-id')
 				.query({ format: 'raw' })

packages/nodes-base/nodes/Google/Gmail/test/v2/utils.test.ts

@@ -2,7 +2,11 @@ import { mock } from 'jest-mock-extended';
 import { DateTime } from 'luxon';
 import type { IExecuteFunctions, INode } from 'n8n-workflow';
 
+import type { IEmail } from '@utils/sendAndWait/interfaces';
+
+import * as GenericFunctions from '../../GenericFunctions';
 import { parseRawEmail, prepareTimestamp } from '../../GenericFunctions';
+import { addThreadHeadersToEmail } from '../../v2/utils/draft';
 
 const node: INode = {
 	id: '1',
@@ -128,3 +132,73 @@ describe('parseRawEmail', () => {
 		expect(typeof json.date).toBe('string');
 	});
 });
+
+describe('addThreadHeadersToEmail', () => {
+	beforeEach(() => {
+		jest.clearAllMocks();
+	});
+
+	it('should set inReplyTo and reference on the email object', async () => {
+		const mockThreadId = 'thread123';
+		const mockMessageId = '<message-id@example.com>';
+		const mockThread = {
+			messages: [
+				{ payload: { headers: [{ value: '<old-id@example.com>' }] } },
+				{ payload: { headers: [{ value: mockMessageId }] } },
+			],
+		};
+
+		jest.spyOn(GenericFunctions, 'googleApiRequest').mockImplementation(async function () {
+			return mockThread;
+		});
+
+		const email = mock<IEmail>({});
+
+		const thisArg = mock<IExecuteFunctions>({});
+
+		await addThreadHeadersToEmail.call(thisArg, email, mockThreadId);
+
+		expect(email.inReplyTo).toBe(mockMessageId);
+		expect(email.reference).toBe(mockMessageId);
+	});
+
+	it('should set inReplyTo and reference on the email object even if the message has only one item', async () => {
+		const mockThreadId = 'thread123';
+		const mockMessageId = '<message-id@example.com>';
+		const mockThread = {
+			messages: [{ payload: { headers: [{ value: mockMessageId }] } }],
+		};
+
+		jest.spyOn(GenericFunctions, 'googleApiRequest').mockImplementation(async function () {
+			return mockThread;
+		});
+
+		const email = mock<IEmail>({});
+
+		const thisArg = mock<IExecuteFunctions>({});
+
+		await addThreadHeadersToEmail.call(thisArg, email, mockThreadId);
+
+		expect(email.inReplyTo).toBe(mockMessageId);
+		expect(email.reference).toBe(mockMessageId);
+	});
+
+	it('should not do anything if the thread has no messages', async () => {
+		const mockThreadId = 'thread123';
+		const mockThread = {};
+
+		jest.spyOn(GenericFunctions, 'googleApiRequest').mockImplementation(async function () {
+			return mockThread;
+		});
+
+		const email = mock<IEmail>({});
+
+		const thisArg = mock<IExecuteFunctions>({});
+
+		await addThreadHeadersToEmail.call(thisArg, email, mockThreadId);
+
+		// We are using mock<IEmail>({}) which means the value of these will be a mock function
+		expect(typeof email.inReplyTo).toBe('function');
+		expect(typeof email.reference).toBe('function');
+	});
+});

packages/nodes-base/nodes/Google/Gmail/v2/DraftDescription.ts

@@ -66,6 +66,13 @@ export const draftFields: INodeProperties[] = [
 		},
 		placeholder: 'Hello World!',
 	},
+	{
+		displayName: 'To reply to an existing thread, specify the exact subject title of that thread.',
+		name: 'threadNotice',
+		type: 'notice',
+		default: '',
+		displayOptions: { show: { resource: ['draft'], operation: ['create'] } },
+	},
 	{
 		displayName: 'Email Type',
 		name: 'emailType',

packages/nodes-base/nodes/Google/Gmail/v2/GmailV2.node.ts

@@ -13,6 +13,7 @@ import { labelFields, labelOperations } from './LabelDescription';
 import { getGmailAliases, getLabels, getThreadMessages } from './loadOptions';
 import { messageFields, messageOperations } from './MessageDescription';
 import { threadFields, threadOperations } from './ThreadDescription';
+import { addThreadHeadersToEmail } from './utils/draft';
 import { configureWaitTillDate } from '../../../../utils/sendAndWait/configureWaitTillDate.util';
 import { sendAndWaitWebhooksDescription } from '../../../../utils/sendAndWait/descriptions';
 import type { IEmail } from '../../../../utils/sendAndWait/interfaces';
@@ -560,6 +561,12 @@ export class GmailV2 implements INodeType {
 							attachments,
 						};
 
+						if (threadId && options.replyTo) {
+							// If a threadId is set, we need to add the Message-ID of the last message in the thread
+							// to the email so that Gmail can correctly associate the draft with the thread
+							await addThreadHeadersToEmail.call(this, email, threadId);
+						}
+
 						const body = {
 							message: {
 								raw: await encodeEmail(email),

packages/nodes-base/nodes/Google/Gmail/v2/utils/draft.ts

@@ -0,0 +1,30 @@
+import type { IExecuteFunctions } from 'n8n-workflow';
+
+import type { IEmail } from '@utils/sendAndWait/interfaces';
+
+import { googleApiRequest } from '../../GenericFunctions';
+
+/**
+ * Adds inReplyTo and reference headers to the email if threadId is provided.
+ */
+export async function addThreadHeadersToEmail(
+	this: IExecuteFunctions,
+	email: IEmail,
+	threadId: string,
+): Promise<void> {
+	const thread = await googleApiRequest.call(
+		this,
+		'GET',
+		`/gmail/v1/users/me/threads/${threadId}`,
+		{},
+		{ format: 'metadata', metadataHeaders: ['Message-ID'] },
+	);
+
+	if (thread?.messages) {
+		const lastMessage = thread.messages.length - 1;
+		const messageId: string = thread.messages[lastMessage].payload.headers[0].value;
+
+		email.inReplyTo = messageId;
+		email.reference = messageId;
+	}
+}