Vercel adapter for tRPC

createVercelApiAdapter.ts

import { AnyRouter, TRPCError } from "@trpc/server";
import {
  NodeHTTPCreateContextFnOptions,
  NodeHTTPHandlerOptions,
  nodeHTTPRequestHandler,
} from "@trpc/server/dist/adapters/node-http";
import { VercelApiHandler, VercelRequest, VercelResponse } from "@vercel/node";
import Cors from "cors";

const cors = Cors();

export type CreateVercelContextOptions = NodeHTTPCreateContextFnOptions<
  VercelRequest,
  VercelResponse
>;

function runMiddleware(req: VercelRequest, res: VercelResponse, fn: any) {
  return new Promise((resolve, reject) => {
    fn(req, res, (result: any) => {
      if (result instanceof Error) {
        return reject(result);
      }

      return resolve(result);
    });
  });
}

export function withCors(handler: VercelApiHandler) {
  return async (req: VercelRequest, res: VercelResponse) => {
    await runMiddleware(req, res, cors);

    return await handler(req, res);
  };
}

export function createVercelApiAdapter<TRouter extends AnyRouter>(
  opts: NodeHTTPHandlerOptions<TRouter, VercelRequest, VercelResponse>
): VercelApiHandler {
  return async (req, res) => {
    function getPath(): string | null {
      if (typeof req.query.trpc === "string") {
        return req.query.trpc;
      }
      if (Array.isArray(req.query.trpc)) {
        return req.query.trpc.join("/");
      }
      return null;
    }
    const path = getPath();

    if (path === null) {
      const error = opts.router.getErrorShape({
        error: new TRPCError({
          message:
            'Query "trpc" not found - is the file named `[trpc]`.ts or `[...trpc].ts`?',
          code: "INTERNAL_SERVER_ERROR",
        }),
        type: "unknown",
        ctx: undefined,
        path: undefined,
        input: undefined,
      });
      res.statusCode = 500;
      res.json({
        id: -1,
        error,
      });
      return;
    }

    await nodeHTTPRequestHandler({
      ...opts,
      req,
      res,
      path,
    });
  };
}