Skill

server-side-calls

Name: server-side-calls
Author: tRPC

execute tRPC procedures from server code

Published by tRPC Updated Jul 18

Covers Backend tRPC API Development Testing

Description

Call tRPC procedures directly from server code using t.createCallerFactory() and router.createCaller(context) for integration testing, internal server logic, and custom API endpoints. Catch TRPCError and extract HTTP status with getHTTPStatusCodeFromError(). Error handling via onError option.

SKILL.md

tRPC -- Server-Side Calls

Setup

// server/trpc.ts
import { initTRPC } from '@trpc/server';

type Context = { user?: { id: string } };

const t = initTRPC.context<Context>().create();

export const router = t.router;
export const publicProcedure = t.procedure;
export const createCallerFactory = t.createCallerFactory;

// server/appRouter.ts
import { TRPCError } from '@trpc/server';
import { z } from 'zod';
import { createCallerFactory, publicProcedure, router } from './trpc';

interface Post {
  id: string;
  title: string;
}

const posts: Post[] = [{ id: '1', title: 'Hello world' }];

export const appRouter = router({
  post: router({
    add: publicProcedure
      .input(z.object({ title: z.string().min(2) }))
      .mutation(({ input }) => {
        const post: Post = { ...input, id: `${Math.random()}` };
        posts.push(post);
        return post;
      }),
    byId: publicProcedure
      .input(z.object({ id: z.string() }))
      .query(({ input }) => {
        const post = posts.find((p) => p.id === input.id);
        if (!post) throw new TRPCError({ code: 'NOT_FOUND' });
        return post;
      }),
    list: publicProcedure.query(() => posts),
  }),
});

export type AppRouter = typeof appRouter;
export const createCaller = createCallerFactory(appRouter);

// usage
import { createCaller } from './appRouter';

const caller = createCaller({ user: { id: '1' } });
const postList = await caller.post.list();
const newPost = await caller.post.add({ title: 'New post' });

Core Patterns

Integration test with createCallerFactory

// server/appRouter.test.ts
import type { inferProcedureInput } from '@trpc/server';
import { createCaller } from './appRouter';
import type { AppRouter } from './appRouter';
import { createContextInner } from './context';

async function testAddAndGetPost() {
  const ctx = await createContextInner({ user: undefined });
  const caller = createCaller(ctx);

  const input: inferProcedureInput<AppRouter['post']['add']> = {
    title: 'Test post',
  };

  const post = await caller.post.add(input);
  const allPosts = await caller.post.list();

  console.assert(allPosts.some((p) => p.id === post.id));
}

Using router.createCaller() directly

import { initTRPC } from '@trpc/server';
import { z } from 'zod';

const t = initTRPC.create();

const appRouter = t.router({
  greeting: t.procedure
    .input(z.object({ name: z.string() }))
    .query(({ input }) => `Hello ${input.name}`),
});

const caller = appRouter.createCaller({});
const result = await caller.greeting({ name: 'tRPC' });

Error handling in a custom API endpoint

import { TRPCError } from '@trpc/server';
import { getHTTPStatusCodeFromError } from '@trpc/server/http';
import type { NextApiRequest, NextApiResponse } from 'next';
import { appRouter } from './appRouter';

export default async function handler(
  req: NextApiRequest,
  res: NextApiResponse,
) {
  const caller = appRouter.createCaller({});

  try {
    const post = await caller.post.byId({ id: req.query.id as string });
    res.status(200).json({ data: { postTitle: post.title } });
  } catch (cause) {
    if (cause instanceof TRPCError) {
      const httpStatusCode = getHTTPStatusCodeFromError(cause);
      res.status(httpStatusCode).json({ error: { message: cause.message } });
      return;
    }
    res.status(500).json({ error: { message: 'Internal server error' } });
  }
}

Caller with onError callback

import { initTRPC } from '@trpc/server';
import { z } from 'zod';

const t = initTRPC.create();

const appRouter = t.router({
  greeting: t.procedure
    .input(z.object({ name: z.string() }))
    .query(({ input }) => {
      if (input.name === 'invalid') {
        throw new Error('Invalid name');
      }
      return `Hello ${input.name}`;
    }),
});

const caller = appRouter.createCaller(
  {},
  {
    onError: (opts) => {
      console.error('An error occurred:', opts.error);
    },
  },
);

Common Mistakes

HIGH Using createCaller inside another procedure

Wrong:

import { appRouter } from './appRouter';
import { createCallerFactory, publicProcedure } from './trpc';

const createCaller = createCallerFactory(appRouter);

const proc = publicProcedure.query(async () => {
  const caller = createCaller({});
  return caller.post.list();
});

Correct:

import type { Context } from './context';
import { publicProcedure } from './trpc';

async function listPosts(ctx: Context) {
  return ctx.db.post.findMany();
}

const proc = publicProcedure.query(async ({ ctx }) => {
  return listPosts(ctx);
});

Calling createCaller from within a procedure re-creates context, re-runs all middleware, and re-validates input; extract shared logic into a plain function instead.

Source: www/docs/server/server-side-calls.md

MEDIUM Not providing context to createCaller

Wrong:

import { appRouter } from './appRouter';

const caller = appRouter.createCaller({});
await caller.protectedRoute();
// middleware throws UNAUTHORIZED because ctx.user is undefined

Correct:

import { appRouter } from './appRouter';
import { createContextInner } from './context';

const ctx = await createContextInner({ user: { id: '1' } });
const caller = appRouter.createCaller(ctx);
await caller.protectedRoute();

createCaller requires a context object matching what procedures and middleware expect; passing an empty object when procedures require auth context causes runtime errors.

Source: www/docs/server/server-side-calls.md

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