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Response Caching

The below examples uses Vercel's edge caching to serve data to your users as fast as possible.

⚠️ A word of caution ⚠️#

Always be careful with caching - especially if you handle personal information.

Since batching is enabled by default, it's recommended to set your cache headers in the responseMeta-function and make sure that there are not any concurrent calls that may include personal data - or to omit cache headers completely if there is an auth headers or cookie.

You can also use a splitLink to split your requests that are public and those that should be private and uncached.

App Caching#

If you turn on SSR in your app you might discover that your app loads slow on for instance Vercel, but you can actually statically render your whole app without using SSG; read this Twitter thread for more insights.

Example code#

// in _app.tsxexport default withTRPC({  config({ ctx }) {    if (process.browser) {      return {        url: '/api/trpc',      };    }
    const url = process.env.VERCEL_URL      ? `https://${process.env.VERCEL_URL}/api/trpc`      : 'http://localhost:3000/api/trpc';
    return {      url,    };  },  ssr: true,  responseMeta({ ctx, clientErrors }) {    if (clientErrors.length) {      // propagate http first error from API calls      return {        status: clientErrors[0].data?.httpStatus ?? 500,      };    }
    // cache request for 1 day + revalidate once every second    const ONE_DAY_IN_SECONDS = 60 * 60 * 24;    return {      headers: {        'cache-control': `s-maxage=1, stale-while-revalidate=${ONE_DAY_IN_SECONDS}`,      }    };  },})(MyApp);

API Response caching#

Since all queries are normal HTTP GETs we can use normal HTTP headers to cache responses, make the responses snappy, give your database a rest, and easier scale your API to gazillions of users.

Using responseMeta to cache responses#

Assuming you're deploying your API somewhere that can handle stale-while-revalidate cache headers like Vercel.

import * as trpc from '@trpc/server';import { inferAsyncReturnType } from '@trpc/server';import * as trpcNext from '@trpc/server/adapters/next';
export const createContext = async ({  req,  res,}: trpcNext.CreateNextContextOptions) => {  return {    req,    res,    prisma,  };};
type Context = inferAsyncReturnType<typeof createContext>;
export function createRouter() {  return trpc.router<Context>();}
const waitFor = async (ms: number) =>  new Promise((resolve) => setTimeout(resolve, ms));
export const appRouter = createRouter()  .query('public.slow-query-cached', {    async resolve({ ctx }) {      await waitFor(5000); // wait for 5s
      return {        lastUpdated: new Date().toJSON(),      };    },  });
// Exporting type _type_ AppRouter only exposes types that can be used for inference// https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-8.html#type-only-imports-and-exportexport type AppRouter = typeof appRouter;
// export API handlerexport default trpcNext.createNextApiHandler({  router: appRouter,  createContext,  responseMeta({ ctx, paths, type, errors }) {    // assuming you have all your public routes with the kewyord `public` in them    const allPublic =      paths && paths.every((path) => path.includes('public'));    // checking that no procedures errored    const allOk = errors.length === 0;    // checking we're doing a query request    const isQuery = type === 'query';
    if (ctx?.res && allPublic && allOk && isQuery) {      // cache request for 1 day + revalidate once every second      const ONE_DAY_IN_SECONDS = 60 * 60 * 24;      return {        headers: {          'cache-control': `s-maxage=1, stale-while-revalidate=${ONE_DAY_IN_SECONDS}`,        },      };    }    return {};  },});