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Tapiduck

What is it?

  • End-to-end typesafe JSON APIs with TypeScript, Zod, and Express.
  • Compile-time type safety, and fullstack IDE intillisense.
  • Inspired by tRPC; but simpler and restful, like JSend.
  • OpenAPI compatible; can auto-generate API docs (Swagger UI)

Motivation

TypeScript is leaps and bounds ahead of JavaScript. Yes, TypeScript can catch/prevent errors, and that’s good. But intillisense is the real game changer. Thanks to IDE auto-complete, you don’t even need to leave your editor to lookup object properties or function params.

While intillisense works great with objects and fucntions that’re defined in TS, it doesn’t quite work with HTTP APIs. On the server, you can’t trust the shape of the request data sent by the client. You need to perform type-narrowing before intellisense kicks in. And on the client, nothing really stops you form accidentally making misshpaed API requests.

Wouldn’t it be nice to have automatic type-validation on the server, so that intellisense kicks in right away? And on the client, wouldn’t it be nice to enforce request shapes at compile-time? That’s exactly what Tapiduck can do for you. It’s a tool for achieving end-to-end typesafety and intellisense.

Quickstart: Typesafe Division API & UI

In this quickstart, we'll start from scratch and build a typesafe API for simple (arithmetic) division, and a typesafe UI for consuming it. Let's get started by setting up the project.

0) Project setup:

Create a directory, and change into it:

mkdir tapiduck-quickstart && cd tapiduck-quickstart;

Set up minimal package.json and tsconfig.json files:

echo '{}' > package.json;
echo '{"compilerOptions":{"esModuleInterop":true,"strict": true}}' > tsconfig.json;

Install dependencies:

npm install --save monoduck zod express cors;
npm install --save-dev typescript @types/express @types/cors parcel ts-node-dev;

Let's create the src/ directory and some empty files:

mkdir src && cd src && touch shared.ts backend.ts frontend.ts frontend.html && cd ..;

1) Define shared endpoint shapes:

In src/shared.ts:

import { tapiduck } from 'monoduck'
import { z } from 'zod'

export const SERVER_PORT = 3000

export const divisionEndpoint = tapiduck.endpoint({
    path: '/api/divide',
    // Define request and response (success & failure) shapes:
    zRequest: z.object({ numerator: z.number(), denominator: z.number() }),
    zSuccess: z.object({ quotient: z.number(), remainder: z.number() }),
    zFail: z.object({message: z.string()})
})

2) On the backend, handle endpoint routes:

In src/backend.ts:

import express from 'express'
import cors from 'cors'
import { tapiduck } from 'monoduck'
import { SERVER_PORT, divisionEndpoint } from './shared'

const app = express().use(cors()).use(express.json())

tapiduck.route(app, divisionEndpoint, async function (reqData, jsend) {
  const { numerator, denominator } = reqData // matches zRequest
  if (denominator === 0) {
    return jsend.fail({ message: 'You cannot divide by zero' }) // matches zFail
  }
  const quotient = Math.floor(numerator / denominator)
  const remainder = numerator % denominator
  return jsend.success({ quotient, remainder }) // must zSuccess
})

app.listen(SERVER_PORT, () => console.log(`Listening @ port ${SERVER_PORT} ...`))

The route handler's first param, reqData, is fully type-validated and intillisense-able. Try typing reqData., and your IDE should suggest numerator and denominator as options.

The second param, jsend , has typed jsend.success() and jsend.fail() helpers. (They also produce the JSend API envelope, hence the name jsend.)

2.5) Start the backend server:

From the project directory (tapiduck-quickstart), run:

npx ts-node-dev src/backend.ts

3) Hit your endpoints from the frontend!

In src/frontend.ts:

import { tapiduck } from 'monoduck'
import { SERVER_PORT, divisionEndpoint } from './shared'

const tapiFetch = tapiduck.fetchUsing(`https://localhost:${SERVER_PORT}`)

const performDivision = async function (): Promise<void> {
  const numerator = Number(window.prompt('Numerator: ', '1'))
  const denominator = Number(window.prompt('Denominator: ', '1'))
  const resp = await tapiFetch(divisionEndpoint, { numerator, denominator })
  if (resp.status !== 'success') {
    // failMsg() is a util for handling non-success responses
    return window.alert(tapiduck.failMsg(resp, data => data.message))
    //                                         ^^^^ matches zFail
  }
  const { quotient, remainder } = resp.data // matches zSuccess
  window.alert(`Quotient: ${quotient}; Remainder: ${remainder}`)
}

window.onload = () => { performDivision() };

tapiFetch is a fetching/request utility bound to the supplied base URL. The first param is an endpoint object (defined via tapiduck.endpoint()). The second param is must match the endpoint's .zRequest shape.

3.5) Start the frontend client:

To try our frontend code, we'll use a minimal HTML webpage and serve it with parcel.

In src/frontend.html:

<h4>Tapiduck Quickstart - Minimal Frontend</h4>
<p>Plesse refresh the page to re-perform division.</p>
<script type="module" src="./frontend.ts"></script>

In a new terminal window, from the project directory (tapiduck-quickstart), run:

npx parcel serve src/frontend.html

Visit the URL reported by parcel (usually https://localhost:1234); and try out the division app!

4) Optional: Auto-Generate API Docs via Swagger UI

Install zod-to-json-schema:

npm install zod-to-json-schema

Import it on the backend (in src/backend.ts):

import { zodToJsonSchema } from 'zod-to-json-schema'

And then, typically right before app.listen():

tapiduck.swaggerfy(app, zodToJsonSchema)

Visit /swagger-ui (i.e. https://localhost:3000/swagger-ui) to check out the API docs! And to see the generated OpenAPI definition, visit /openapi.json.

Quick notes:

  1. For brevity, we defined a single endpoint above; but you could define more!
  2. We used vanilla TS for the frontend here, but you could use React, Vue, Angular etc.
  3. In larger apps, you'd typically have separate frontend/, backend/ and shared/ directories.
    • And yes, instead of separate directories, they could be separate packages.
  4. We passed an express app to tapiduck.route(), but you could pass an express router instead.
  5. You needn't pass the app (or router) each time. tapiduck.routeUsing() helps with that.

Larger Example (FlagLeap)

Looking for a larger example of using Tapiduck for end-to-end typesafety? See FlagLeap (a feature flag management service):

JSend API Envelope

JSend is a lightweight envelope spec for JSON APIs, and Tapiduck adopts it almost exactly.

For an endpoint ept created via tapiduck.endpoint():

  • if a request succeeds:
    • response shape: {status: "success", data: z.infer<typeof ept.zSuccess>}
    • HTTP status: 200 OK
  • if your code rejects the request for any reason:
    • response shape: {status: "fail", data: z.infer<typeof ept.zFail>}
    • HTTP status: 422 Unprocessable Content
  • if there's an unexpected (uncaught) server error:
    • response shape: {status: "error", message: string, code: number}
    • HTTP status: 500 Internal Server Error
    • the code defaults to 500, and is unrelated to the HTTP status
  • if Tapiduck can't zod-validate the request on the server, or the response on the client:
    • response shape: {status: 'zodfail', where: 'server' | 'client', message: string }
    • HTTP status: 400 Bad Request

Status zodfail is Tapiduck-specific; it isn't a part of JSend. If you encounter this error, it's likely that the client is using a stale endpoint definition. You should ask the user to refresh/update the client app.

JSON & CORS Middleware

Tapiduck expects JSON requests, and always produces a JSON response. You should always install the express.json() middleware on your express app (or router). To allow CORS, npm install cors and add the cors() middleware first.

import express from 'express'
import cors from 'cors'
import { tapiduck } from monoduck

const app = express()
app.use(cors()) // optional
app.use(express.json()) // required

tapiduck.route(app, <your-endpoint-here>, <your-handler-here>)

OpenAPI Compatibility

To generate an OpenAPI definition for your Tapiduck API:

Step 1: Install zod-to-json-schema

npm install zod-to-json-schema

Step 2: Provide it to tapiduck (dependency injection):

import { tapiduck } from 'monoduck'
import zodToJsonSchema from 'zod-to-json-schema'

tapiduck.injectZodToJsonSchema(zodToJsonSchema)

Step 3: Generate the definition:

const myOpenApiDefinition = tapiduck.toOpenApi3({
    endpoints: [divisionEndpoint], // Array of TapiEndpoint objects
    serverUrls: [`https://localhost:3000`], // Array of base URLs for the API
    title: 'Todo API', // API title
    version: '0.0.0' // API version
  })