Relay transactional email through Salesforce instead of SMTP (#9)

Reviewed-on: #9
Co-authored-by: Patrick Müller <patrick@mueller-patrick.tech>
Co-committed-by: Patrick Müller <patrick@mueller-patrick.tech>

src/common/common.mail.nodemailer.ts

@@ -1,42 +0,0 @@
-import * as nodemailer from 'nodemailer';
-
-export namespace MailService {
-    const transporter = nodemailer.createTransport({
-        host: process.env.EMAIL_HOST,
-        pool: true,
-        port: 465,
-        secure: true,
-        auth: {
-            user: process.env.EMAIL_USERNAME,
-            pass: process.env.EMAIL_PASSWORD
-        },
-        tls: {rejectUnauthorized: false}
-    });
-
-    export interface MailAttachment {
-        filename: string;
-        content: string | Buffer;
-        contentType?: string;
-    }
-
-    export interface SendMailOptions {
-        html?: string;
-        attachments?: MailAttachment[];
-    }
-
-    // Builds a fresh options object per call rather than mutating a shared
-    // module-level one - the transporter is pooled, so overlapping sendMail
-    // calls (e.g. two guests redeeming at once) previously risked one
-    // call's recipient/subject/body being overwritten by another's before
-    // transporter.sendMail() read it.
-    export const sendMail = async (recipientAddress: string, subject: string, body: string, options?: SendMailOptions) => {
-        await transporter.sendMail({
-            from: 'noreply@nachklang.art',
-            to: recipientAddress,
-            subject: subject,
-            text: body,
-            html: options?.html,
-            attachments: options?.attachments
-        });
-    };
-}

src/common/common.mail.ts

@@ -0,0 +1,107 @@
+import logger from '../middleware/logger';
+import {salesforceApexRestPost, salesforceEnabled} from './salesforce.client';
+
+// Transactional email for the ticketing/calendar flows (voucher redemption
+// confirmations, account activation links, password-reset tokens) is relayed
+// through the Nachklang Salesforce org rather than sent over our own SMTP host:
+// that host's IP reputation gets it blocked by allowlist-based receivers
+// (notably t-online.de). Salesforce's MTA plus the org's DKIM signature for
+// nachklang.art get the mail delivered. The org endpoint is EmailSendResource
+// (POST /services/apexrest/email/send); the From address is fixed server-side
+// there and is never sent from here.
+//
+// sendMail never throws on a delivery problem. Every caller has already
+// committed its own work (a registration, a password-reset token, a
+// redemption) by the time mail goes out, so a mail failure must not surface as
+// a user-facing error. It returns whether the mail was accepted so the one
+// caller that shows failures to staff (the voucher confirmation) can record it.
+
+export namespace MailService {
+	export interface MailAttachment {
+		filename: string;
+		content: string | Buffer;
+		contentType?: string;
+	}
+
+	export interface SendMailOptions {
+		html?: string;
+		attachments?: MailAttachment[];
+	}
+
+	interface EmailSendResponse {
+		status: 'SENT';
+	}
+
+	// Practical ceiling, well under Apex REST's 6 MB request-body limit once
+	// base64 inflation (~33%) is accounted for. The only attachment today is a
+	// ~1 KB .ics file.
+	const MAX_ATTACHMENT_BYTES = 3 * 1024 * 1024;
+
+	const isRetriable = (err: any): boolean => {
+		const status = err?.response?.status;
+		if (status !== undefined) {
+			return status >= 500;
+		}
+		// No response at all - network error or timeout.
+		return true;
+	};
+
+	/**
+	 * Relays one email through the Salesforce org. Retries once on a transient
+	 * failure (5xx / network / timeout), then logs and returns false rather
+	 * than throwing. Returns false immediately (without a callout) when the
+	 * Salesforce integration is disabled.
+	 */
+	export const sendMail = async (
+		recipientAddress: string,
+		subject: string,
+		body: string,
+		options?: SendMailOptions
+	): Promise<boolean> => {
+		if (!salesforceEnabled()) {
+			logger.info('MailService: SALESFORCE_ENABLED is false, would have sent', {recipientAddress, subject});
+			return false;
+		}
+
+		let attachments: {filename: string; contentType?: string; contentBase64: string}[];
+		try {
+			attachments = (options?.attachments ?? []).map(attachment => {
+				const buffer = Buffer.isBuffer(attachment.content)
+					? attachment.content
+					: Buffer.from(attachment.content, 'utf-8');
+				if (buffer.byteLength > MAX_ATTACHMENT_BYTES) {
+					throw new Error(`attachment ${attachment.filename} is ${buffer.byteLength} bytes, over the ${MAX_ATTACHMENT_BYTES} limit`);
+				}
+				return {filename: attachment.filename, contentType: attachment.contentType, contentBase64: buffer.toString('base64')};
+			});
+		} catch (err: any) {
+			logger.error('MailService: could not prepare attachments', {recipientAddress, subject, detail: err?.message});
+			return false;
+		}
+
+		const payload = {
+			to: recipientAddress,
+			subject,
+			textBody: body,
+			htmlBody: options?.html ?? null,
+			attachments
+		};
+
+		for (let attempt = 1; attempt <= 2; attempt++) {
+			try {
+				await salesforceApexRestPost<EmailSendResponse>('/services/apexrest/email/send', payload);
+				return true;
+			} catch (err: any) {
+				const status = err?.response?.status;
+				const detail = err?.response?.data?.errorCode || err?.response?.data?.message || err?.message || 'unknown error';
+				if (attempt === 1 && isRetriable(err)) {
+					logger.warn('MailService: send failed, retrying once', {recipientAddress, subject, status, detail});
+					continue;
+				}
+				logger.error('MailService: send failed', {recipientAddress, subject, status, detail});
+				return false;
+			}
+		}
+		return false;
+	};
+}

src/common/salesforce.client.ts

@@ -0,0 +1,66 @@
+import axios from 'axios';
+
+// Shared server-to-server access to the one Nachklang Salesforce org. Both the
+// newsletter-signup sync (feedback module) and the transactional-email relay
+// (common.mail) authenticate the same way - OAuth 2.0 client credentials
+// against the nk_Nachklang_API_Integration external client app - so the token
+// cache and the retry-once-on-401 live here rather than being duplicated.
+//
+// Salesforce's client-credentials token response does not reliably include
+// expires_in, so the cache lifetime is a conservative guess rather than a
+// value read from the response - a 401 on the next call just triggers a fresh
+// fetch (see salesforceApexRestPost).
+
+const TOKEN_CACHE_MS = 15 * 60 * 1000;
+let cachedToken: {accessToken: string; fetchedAt: number} | null = null;
+
+export const salesforceEnabled = (): boolean => process.env.SALESFORCE_ENABLED === 'true';
+
+const readConfig = (): {instanceUrl: string; clientId: string; clientSecret: string} => {
+	const instanceUrl = process.env.SALESFORCE_API_URL;
+	const clientId = process.env.SALESFORCE_CLIENT_ID;
+	const clientSecret = process.env.SALESFORCE_CLIENT_SECRET;
+	if (!instanceUrl || !clientId || !clientSecret) {
+		throw new Error('SALESFORCE_ENABLED is true but SALESFORCE_API_URL/SALESFORCE_CLIENT_ID/SALESFORCE_CLIENT_SECRET are not fully configured.');
+	}
+	return {instanceUrl, clientId, clientSecret};
+};
+
+const getAccessToken = async (forceRefresh: boolean): Promise<string> => {
+	if (!forceRefresh && cachedToken && Date.now() - cachedToken.fetchedAt < TOKEN_CACHE_MS) {
+		return cachedToken.accessToken;
+	}
+
+	const {instanceUrl, clientId, clientSecret} = readConfig();
+	const res = await axios.post(
+		`${instanceUrl}/services/oauth2/token`,
+		new URLSearchParams({grant_type: 'client_credentials', client_id: clientId, client_secret: clientSecret}).toString(),
+		{headers: {'Content-Type': 'application/x-www-form-urlencoded'}, timeout: 10000}
+	);
+	cachedToken = {accessToken: res.data.access_token, fetchedAt: Date.now()};
+	return cachedToken.accessToken;
+};
+
+/**
+ * POSTs a JSON body to an Apex REST path (e.g. '/services/apexrest/newsletter/signup')
+ * and returns the parsed response body. Retries once with a forced token
+ * refresh on a 401 - the server-side token may have expired even though our
+ * conservative local TTL has not. All other errors propagate to the caller.
+ */
+export const salesforceApexRestPost = async <T>(path: string, body: unknown): Promise<T> => {
+	const {instanceUrl} = readConfig();
+	const url = `${instanceUrl}${path}`;
+
+	try {
+		const token = await getAccessToken(false);
+		const res = await axios.post<T>(url, body, {headers: {Authorization: `Bearer ${token}`}, timeout: 10000});
+		return res.data;
+	} catch (err: any) {
+		if (err?.response?.status === 401) {
+			const token = await getAccessToken(true);
+			const res = await axios.post<T>(url, body, {headers: {Authorization: `Bearer ${token}`}, timeout: 10000});
+			return res.data;
+		}
+		throw err;
+	}
+};