Links & Request Batching

Similar to urql's exchanges or Apollo's links. Links enables you to customize the flow of data between tRPC Client and the tRPC-server.

Request Batching

Request batching is automatically enabled which batches your requests to the server, this can make the below code produce exactly one HTTP request and on the server exactly one database query:

// below will be done in the same request when batching is enabled
const somePosts = await Promise.all([
  proxy.post.byId.query(1);
  proxy.post.byId.query(2);
  proxy.post.byId.query(3);
])

Customizing data flow

The below examples assuming you use Next.js, but the same as below can be added if you use the vanilla tRPC client

Setting a maximum URL length

When sending batch requests, sometimes the URL can become too large causing HTTP errors like 413 Payload Too Large, 414 URI Too Long, and 404 Not Found. The maxURLLength option will limit the number of requests that can be sent together in a batch.

utils/trpc.ts

import { setupTRPC } from '@trpc/next';
import type { AppRouter } from "@/server/routers/app";

export const trpc = setupTRPC<AppRouter>({
  config() {
    return {
      links: [
        httpBatchLink({
          url: 'http://localhost:3000/api/trpc',
          maxURLLength: 2083 // a suitable size
        }),
      ],
    };
  },
});

Disabling request batching

1. Disable batching on your server:

In your [trpc].ts:

pages/api/trpc/[trpc].ts

export default trpcNext.createNextApiHandler({
  // [...]
  // 👇 disable batching
  batching: {
    enabled: false,
  },
});

2. Use batch-free link in your tRPC Client

utils/trpc.ts

import { setupTRPC } from '@trpc/next';
import type { AppRouter } from "@/server/routers/app";
import { httpLink } from '@trpc/client';

export const trpc = setupTRPC<AppRouter>({
  config() {
    return {
      links: [
        httpLink({
          url: '/api/trpc',
        }),
      ],
    };
  },
});

Using a splitLink to control request flow

Disable batching for certain requests

1. Configure client / utils/trpc.ts

utils/trpc.ts

import { setupTRPC } from '@trpc/next';
import { httpBatchLink, httpLink, splitLink } from '@trpc/client';

export default setupTRPC<AppRouter>({
  config() {
    const url = `http://localhost:3000`;

    return {
      links: [
        splitLink({
          condition(op) {
            // check for context property `skipBatch`
            return op.context.skipBatch === true;
          },
          // when condition is true, use normal request
          true: httpLink({
            url,
          }),
          // when condition is false, use batching
          false: httpBatchLink({
            url,
          }),
        }),
      ],
    };
  },
});

2. Perform request without batching

MyComponent.tsx

export function MyComponent() {
  const postsQuery = proxy.posts.useQuery({
    context: {
      skipBatch: true,
    },
  });
  return (
    <pre>{JSON.stringify(postsQuery.data ?? null, null, 4)}</pre>
  )
})

or:

client.ts

const postResult = proxy.posts.query(null, {
  context: {
    skipBatch: true,
  },
})

Creating a custom link

Reference examples can be found in packages/client/src/links.

utils/customLink.ts

import { TRPCLink } from '@trpc/client';
import { AppRouter } from 'server/routers/_app';
import { observable } from '@trpc/server/observable';

export const customLink: TRPCLink<AppRouter> = () => {
  // here we just got initialized in the app - this happens once per app
  // useful for storing cache for instance
  return ({ next, op }) => {
    // this is when passing the result to the next link

    // each link needs to return an observable which propagates results
    return observable((observer) => {
      console.log('performing operation:', op);
      const unsubscribe = next(op).subscribe({
        next(value) {
          console.log('we received value', value);
          observer.next(value);
        },
        error(err) {
          console.log('we received error', err);
          observer.error(err);
        },
        complete() {
          observer.complete();
        },
      });

      return unsubscribe;
    });
  };
};