Output data validation for tRPC

output.ts

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

/**
 * Output parser. Example use-cases:
 * - Resolvers where you touch sensitive data that you don't wanna risk leaking
 * - Hairy resolvers where it's hard to follow what the resolver returns
 * @param schema Zod Schema
 * @param output The output
 * @returns A parsed output, guaranteed to conform to the schema
 */
export function output<TSchema extends z.ZodTypeAny>(
  schema: TSchema,
  output: TSchema['_input'],
): TSchema['_output'] {
  try {
    return schema.parse(output);
  } catch (cause) {
    throw new TRPCError({
      code: 'INTERNAL_SERVER_ERROR',
      message: 'Output validation failed',
      cause,
    });
  }
}

postRouter.ts

import { createRouter } from 'server/createRouter';
import { z } from 'zod';
import { TRPCError } from '@trpc/server';
import { output } from 'server/lib/output';

export const postRouter = createRouter()
  .query('byId', {
    input: z.object({
      id: z.string(),
    }),
    async resolve({ ctx, input }) {
      const { id } = input;
      const post = await ctx.prisma.post.findUnique({
        where: { id },
        select: {
          id: true,
          title: true,
          text: true,
          createdAt: true,
          updatedAt: true,
        },
      });
      if (!post) {
        throw new TRPCError({
          code: 'NOT_FOUND',
          message: `No post with id '${id}'`,
        });
      }
      // Strictly validate the output before returning the result
      return output(
        z.object({
          id: z.string(),
          title: z.string(),
          text: z.string(),
          createdAt: z.date(),
          updatedAt: z.date(),
        }),
        post,
      );
    },
  })