typera-openapi - OpenAPI generator for typera

typera-openapi is an tool that automatically creates OpenAPI v3 definitions for projects that use typera for routes.

Upgrading to v2? See the upgrading instructions.

Table of Contents

• Getting started
• CLI
• How it works?
  • The Date type
• Reference
• Releasing

Getting started

Install typera-openapi:

npm install typera-openapi

Your route files must have a single default export that exports a typera router. JSDoc comments serve as additional documentation:

// src/my-routes.ts

import { Response, Route, route, router } from 'typera-express'

interface MyResult {
  /** The JSDoc text is used as a description for object properties */
  field: number
}

const bodyCodec = t.type({
  /** Descriptions are also supported in io-ts codecs
   * @example Lets you set an example value for a particular property
   */
  name: t.string
})

/**
 * Routes can also have a description. Note that descriptions are entirely optional.
 *
 * @summary You can also set a short summary
 * @tags Tag1, Tag2
 *
 * @routeParam myRouteParam Description for route parameter
 *
 * @response 200 Success response description.
 * @response 400 Another description for a response. This one
 * spans multile lines.
 */
const myRoute: Route<Response.Ok<MyResult> | Response.BadRequest<string>> =
  route.post(...).use(Parser.body(bodyCodec)).handler(...)

// ...

/**
 * @prefix /api
 * @tags Tag3
 */
export default router(myRoute, ...)

// The optional @prefix JSDoc tag prepends the prefix to all route paths.
// Tags from router are added to all its routes.

Run the typera-openapi tool giving paths to your route files as command line arguments:

npx typera-openapi src/my-routes.ts

This creates src/my-routes.openapi.ts which contains the OpenAPI definitions.

Use the definitions in your app to serve documentation:

// src/app.ts

import * as express from 'express'
import { OpenAPIV3 } from 'openapi-types'
import * as swaggerUi from 'swagger-ui-express'
import { prefix } from 'typera-openapi'

import myRoutes from './my-routes'
import openapi from './openapi'

const openapiDoc: OpenAPIV3.Document = {
  openapi: '3.0.0',
  info: {
    title: 'My cool API',
    version: '0.1.0',
  },
  ...openapi,
}

const app = express()
app.use('/api', myRoutes.handler())
app.use('/api-docs', swaggerUi.serve, swaggerUi.setup(openapiDoc))
app.listen(3000)

CLI

typera-openapi [options] FILE...

Generate OpenAPI definitions for routes found in the given files.

Options:

-o OUTFILE, --outfile OUTFILE

Output file name. Must end in either .ts or .json.

--prettify, -p

Apply prettier formatting to output files.

--check, -c

Check that the output file is up-to-date without actually writing it. If the file is outdated, print an error and exit with status 1. Useful for CI.

How it works?

typera-openapi uses TypeScript type information to generate OpenAPI definitions. Methods, paths, route params, query params, request and response bodies, and request and response headers are determined by looking up the type information provided by the TypeScript compiler API.

For example, assume we have this route:

/**
 * @response 200 User created successfully
 * @response 400 Validation error
 */
const createUser: Route<Response.Ok<User> | Response.BadRequest<string>> = route
  .post('/users')
  .use(Parser.body(createUserBody))
  .handler(async (request) => { ... })

• Response descriptions are looked up from the JSDoc comment. Other tags are also available.
• Response body and header types are available in the type of the createUser variable. The explicit type annotation would not even be needed, because the compiler can infer the type.
• Method and path are available in the .post('/users') call.
• The rest are looked up by inspecting the type of the request parameter of the route handler function.

This has one caveat: The request type must match the input you expect your user to send. Assume the createUserBody codec is like this:

const createUserBody = t.type({
  name: t.string,
  shoeSize: t.number,
  allowMarketing: BooleanFromString, // from io-ts-types
})

The name and shoeSize fields are fine, since both t.string and t.number map their input type to the same output type. But the allowMarketing field is problematic, since BooleanFromString takes a string as an input, but converts it to boolean.

So the JSON input this route expects is:

type Input = {
  name: string
  shoeSize: number
  allowMarketing: string
}

But the type of request.body that the compiler sees is:

type Body = {
  name: string
  shoeSize: number
  allowMarketing: boolean
}

For this reason, you shouldn't use decoders that change the type of the input directly. If needed, you should instead add another step for converting the data from input to the format you expect. This can be achieved with a custom middleware, for example.

The Date type

JSON doesn't have a native Date type. As explained above, when typera-openapi encounters a Date type, it doesn't know from which input type it is parsed, so it uses string and sets format to date-time, because this is how JSON.stringify encodes Date objects by default. In the future we may add a way to override this behavior.

Reference

Terms:

• Route means an OpenAPI operation, i.e. an endpoint you can request.
• route is the typera object that lets you create routes, see the docs.
• Route handler is the function passed to .handler() when defining a route
• request is the sole parameter of the route handler function.
• Route type is the type of the route variable returned by route.get() etc.
• Router is the value returned by router().

For each route, typera-openapi determines the following information:

Information	Source
method	Which route method is called, e.g. route.get()
path	The parameter of e.g. route.get()
summary	JSDoc comment's @summary tag
description	JSDoc comment's text
tags	JSDoc comment's @tags
operationId	Name of the variable that holds the route, override with JSDoc comment's @operationId
parameters	See table below
request body	See table below
responses	See table below

The JSDoc comment of the router can be used to add information to all its routes:

Information	Source
path prefix	JSDoc comment's @path tag is prefixed to all routes
tags	JSDoc comment's @tags are added to all routes

OpenAPI parameters covers all the other input expect the request body:

Parameter	Source
path	Route parameter captures
query	The type of request.query (the output of Parser.query or custom middleware)
header	The type of request.headers (the output of Parser.headers or custom middleware)
cookie	The type of request.cookies (the output of Parser.cookies or custom middleware)

OpenAPI allows different request body types per content type, but typera-openapi only allows one.

Body field	Source
content type	request.contentType, or 'application/json' if not defined
schema	The type of request.body (the output of Parser.body or custom middleware)

A route can have multiple responses. These are modeled in the route type as Route<Response1 | Response2 | ...>. See the docs. Each response type adds a response to the OpenAPI document.

Response field	Source
status	Response's Status type (number literal type)
description	JSDoc comment's @response tag
content type	See below
content schema	Response's Body type
headers	Response's Headers type

Response's content type is determined as follows:

• text/plain if the body type is string or number
• application/octet-stream for streaming responses
• application/json otherwise

Releasing

$ yarn version --new-version <major|minor|patch>
$ yarn publish
$ git push origin main --tags

Open https://github.com/akheron/typera-openapi/releases, edit the draft release, select the newest version tag, adjust the description as needed.