tRPC to OpenAPI generator

Note: I do not want to have this as part of the library itself, but an example would be good

Overview

With the addition of output parser (#1699), we should now have all the pieces to automatically create an OpenAPI-compliant endpoint

Some rough ideas:

• Create a new endpoint /api/openapi.yml.ts that can use the method earlier to generate a schema
• Create a catch-all /api/openapi/[...params].ts that can dynamically read and call tRPC queries
• https://github.com/StefanTerdell/zod-to-json-schema#readme can be useful
• Example how to create JSON schema from tRPC routes: https://gist.github.com/KATT/993fbcbaf123f08098a154631e5af68c
• This package can be of good inspo for the openapi output https://github.com/RobinTail/express-zod-api

A starting point for the api handler:

import { ProcedureType, TRPCError } from '@trpc/server';
import { NextApiRequest, NextApiResponse } from 'next';
import { createContext } from '~/server/context';
import { appRouter } from '~/server/routers/_app';

export default async function swag(req: NextApiRequest, res: NextApiResponse) {
  const { params, ...queryParams } = req.query;
  if (req.method !== 'POST' && req.method !== 'GET') {
    res.status(405).json({
      message: 'Invalid method',
    });
    return;
  }
  const path = Array.isArray(params) ? params.join('/') : params;
  const ctx = await createContext({ req, res });
  const type: ProcedureType = req.method === 'POST' ? 'mutation' : 'query';
  try {
    const caller = appRouter.createCaller({ ctx });

    const fn = caller[type] as any;
    const result = await fn(path, queryParams);

    res.json(result);
    return;
  } catch (error) {
    if (!(error instanceof TRPCError)) {
      res.status(500).json({
        message: 'Something went wrong',
      });
      return;
    }
    const formatted = appRouter.getErrorShape({
      error,
      path,
      ctx,
      input: params,
      type,
    });
    // TODO: use https://github.com/trpc/trpc/blob/main/packages/server/src/http/internals/getHTTPStatusCode.ts#L55-L59
    // Feel free to make them publicly exposed
    const status = 500;
    res.status(500).json(formatted);
  }
}

[jlalmes]

You can try out the alpha release of trpc-openapi that is compatible with the current stable version of @trpc/server@9. Bear in mind that the API may change before official release.

https://www.npmjs.com/package/trpc-openapi

[jlalmes]

@Brian-McBride I plan to publish my trpc-openapi work promptly after tRPC v10 is released.