feat: add rate limiting and more error handling to Cal.ai

apps/ai/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@calcom/ai",
-  "version": "1.2.0",
+  "version": "1.2.1",
   "private": true,
   "author": "Cal.com Inc.",
   "dependencies": {

apps/ai/src/app/api/agent/route.ts

@@ -40,6 +40,13 @@ export const POST = async (request: NextRequest) => {
 
     return new NextResponse("ok");
   } catch (error) {
+    await sendEmail({
+      subject: `Re: ${subject}`,
+      text: "Thanks for using Cal.ai! We're experiencing high demand and can't currently process your request. Please try again later.",
+      to: user.email,
+      from: agentEmail,
+    });
+
     return new NextResponse(
       (error as Error).message || "Something went wrong. Please try again or reach out for help.",
       { status: 500 }

apps/ai/src/app/api/receive/route.ts

@@ -3,6 +3,7 @@ import { simpleParser } from "mailparser";
 import type { NextRequest } from "next/server";
 import { NextResponse } from "next/server";
 
+import { checkRateLimitAndThrowError } from "@calcom/lib/checkRateLimitAndThrowError";
 import prisma from "@calcom/prisma";
 
 import { env } from "../../../env.mjs";
@@ -31,18 +32,37 @@ export const POST = async (request: NextRequest) => {
 
   const formData = await request.formData();
   const body = Object.fromEntries(formData);
-
-  // body.dkim looks like {@domain-com.22222222.gappssmtp.com : pass}
-  const signature = (body.dkim as string).includes(" : pass");
-
   const envelope = JSON.parse(body.envelope as string);
 
   const aiEmail = envelope.to[0];
+  const subject = body.subject || "";
+
+  try {
+    await checkRateLimitAndThrowError({
+      identifier: `ai:email:${envelope.from}`,
+      rateLimitingType: "ai",
+    });
+  } catch (error) {
+    await sendEmail({
+      subject: `Re: ${subject}`,
+      text: "Thanks for using Cal.ai! You've reached your daily limit. Please try again tomorrow.",
+      to: envelope.from,
+      from: aiEmail,
+    });
+
+    return new NextResponse("Exceeded rate limit", { status: 200 }); // Don't return 429 to avoid triggering retry logic in SendGrid
+  }
 
   // Parse email from mixed MIME type
   const parsed: ParsedMail = await simpleParser(body.email as Source);
 
   if (!parsed.text && !parsed.subject) {
+    await sendEmail({
+      subject: `Re: ${subject}`,
+      text: "Thanks for using Cal.ai! It looks like you forgot to include a message. Please try again.",
+      to: envelope.from,
+      from: aiEmail,
+    });
     return new NextResponse("Email missing text and subject", { status: 400 });
   }
 
@@ -62,11 +82,14 @@ export const POST = async (request: NextRequest) => {
     where: { email: envelope.from },
   });
 
+  // body.dkim looks like {@domain-com.22222222.gappssmtp.com : pass}
+  const signature = (body.dkim as string).includes(" : pass");
+
   // User is not a cal.com user or is using an unverified email.
   if (!signature || !user) {
     await sendEmail({
       html: `Thanks for your interest in Cal.ai! To get started, Make sure you have a <a href="https://cal.com/signup" target="_blank">cal.com</a> account with this email address.`,
-      subject: `Re: ${body.subject}`,
+      subject: `Re: ${subject}`,
       text: `Thanks for your interest in Cal.ai! To get started, Make sure you have a cal.com account with this email address. You can sign up for an account at: https://cal.com/signup`,
       to: envelope.from,
       from: aiEmail,
@@ -83,7 +106,7 @@ export const POST = async (request: NextRequest) => {
 
     await sendEmail({
       html: `Thanks for using Cal.ai! To get started, the app must be installed. <a href=${url} target="_blank">Click this link</a> to install it.`,
-      subject: `Re: ${body.subject}`,
+      subject: `Re: ${subject}`,
       text: `Thanks for using Cal.ai! To get started, the app must be installed. Click this link to install the Cal.ai app: ${url}`,
       to: envelope.from,
       from: aiEmail,
@@ -110,7 +133,7 @@ export const POST = async (request: NextRequest) => {
 
   if ("error" in availability) {
     await sendEmail({
-      subject: `Re: ${body.subject}`,
+      subject: `Re: ${subject}`,
       text: "Sorry, there was an error fetching your availability. Please try again.",
       to: user.email,
       from: aiEmail,
@@ -121,7 +144,7 @@ export const POST = async (request: NextRequest) => {
 
   if ("error" in eventTypes) {
     await sendEmail({
-      subject: `Re: ${body.subject}`,
+      subject: `Re: ${subject}`,
       text: "Sorry, there was an error fetching your event types. Please try again.",
       to: user.email,
       from: aiEmail,
@@ -139,8 +162,8 @@ export const POST = async (request: NextRequest) => {
     body: JSON.stringify({
       apiKey,
       userId: user.id,
-      message: parsed.text,
-      subject: parsed.subject,
+      message: parsed.text || "",
+      subject: parsed.subject || "",
       replyTo: aiEmail,
       user: {
         email: user.email,

packages/lib/checkRateLimitAndThrowError.ts

@@ -1,4 +1,4 @@
-import { TRPCError } from "@calcom/trpc";
+import { TRPCError } from "@calcom/trpc/server";
 
 import type { RateLimitHelper } from "./rateLimit";
 import { rateLimiter } from "./rateLimit";

packages/lib/rateLimit.ts

@@ -7,7 +7,7 @@ import logger from "./logger";
 const log = logger.getChildLogger({ prefix: ["RateLimit"] });
 
 export type RateLimitHelper = {
-  rateLimitingType?: "core" | "forcedSlowMode" | "common" | "api";
+  rateLimitingType?: "core" | "forcedSlowMode" | "common" | "api" | "ai";
   identifier: string;
 };
 
@@ -75,6 +75,12 @@ export function rateLimiter() {
       prefix: "ratelimit:api",
       limiter: Ratelimit.fixedWindow(10, "60s"),
     }),
+    ai: new Ratelimit({
+      redis,
+      analytics: true,
+      prefix: "ratelimit",
+      limiter: Ratelimit.fixedWindow(20, "1d"),
+    }),
   };
 
   async function rateLimit({ rateLimitingType = "core", identifier }: RateLimitHelper) {