Express OpenAPI
A middleware for generating and validating OpenAPI documentation from an Express app.
This middleware will look at the routes defined in your app and fill in as much as it can about them into an OpenAPI document. Optionally you can also flesh out request and response schemas, parameters, and other parts of your api spec with path specific middleware. The final document will be exposed as json served by the main middleware (along with component specific documents).
Note on package name
This package documents itself as @express/openapi. This is because we (the Express TC) have been discussing
adopting the npm scope for publishing "core maintained" middleware modules. This is one such middleware.
While we are working out the details of this I am publishing this module under my personal scope. When
that is resolved we will move it over to the main scope and I will deprecate this module.
Install & usage step for now: $ npm i @wesleytodd/openapi & const openapi = require('@wesleytodd/openapi')
Philosophy
It is common in the OpenAPI community to talk about generating code from documentation. There is value in this approach, as often it is easier for devs to let someone else make the implementation decisions for them. For me, I feel the opposite. I am an engineer whose job it is to make good decisions about writing quality code. I want control of my application, and I want to write code. With this module I can both write great code, as well as have great documentation!
Installation
$ npm install --save @express/openapi
Usage
const openapi = require('@express/openapi')
const app = require('express')()
const oapi = openapi({
openapi: '3.0.0',
info: {
title: 'Express Application',
description: 'Generated docs from an Express api',
version: '1.0.0',
}
})
// This will serve the generated json document(s)
// (as well as swagger-ui or redoc if configured)
app.use(oapi)
// To add path specific schema you can use the .path middleware
app.get('/', oapi.path({
responses: {
200: {
description: 'Successful response',
content: {
'application/json': {
schema: {
type: 'object',
properties: {
hello: { type: 'string' }
}
}
}
}
}
}
}), (req, res) => {
res.json({
hello: 'world'
})
})
app.listen(8080)In the above example you can see the output of the OpenAPI spec by requesting /openapi.json.
$ curl -s http://localhost:8080/openapi.json | jq .
{
"openapi": "3.0.0",
"info": {
"title": "Express Application",
"version": "1.0.0",
"description": "Generated docs from an Express api"
},
"paths": {
"/": {
"get": {
"responses": {
"200": {
"description": "Successful response",
"content": {
"application/json": {
"schema": {
"type": "object",
"properties": {
"hello": {
"type": "string"
}
}
}
}
}
}
}
}
}
}
}Api Docs
openapi([route [, document[, options]]])
Creates an instance of the documentation middleware. The function that is returned is a middleware function decorated with helper methods for setting up the api documentation.
Options:
route <string>: A route for which the documentation will be served atdocument <object>: Base document on top of which the paths will be addedoptions <object>: Options objectoptions.coerce: Enable data typecoercionoptions.htmlui: Turn on servingredocorswagger-uihtml uioptions.basePath: When set, will strip the value ofbasePathfrom the start of every path. The options object can also accept configuration parameters for Swagger and Redoc. The full list of Swagger and Redoc configuration options can be found here: https://swagger.io/docs/open-source-tools/swagger-ui/usage/configuration/ and here: https://redocly.com/docs/redoc/config/ respectively.
Coerce
By default coerceTypes is set to true for AJV, but a copy of the req data
is passed to prevent modifying the req in an unexpected way. This is because
the coerceTypes option in (AJV modifies the input)[ajv-validator/ajv#549].
If this is the behavior you want, you can pass true for this and a copy will not be made.
This will result in params in the path or query with type number will be converted
to numbers based on the rules from AJV.
OpenApiMiddleware.path([definition])
Registers a path with the OpenAPI document. The path definition is an
OperationObject
with all of the information about the requests and responses on that route. It returns
a middleware function which can be used in an express app.
Example:
app.get('/:foo', oapi.path({
description: 'Get a foo',
responses: {
200: {
content: {
'application/json': {
schema: {
type: 'object',
properties: {
foo: { type: 'string' }
}
}
}
}
}
}
}), (req, res) => {
res.json({
foo: req.params.foo
})
})OpenApiMiddleware.validPath([definition])
Registers a path with the OpenAPI document, also ensures incoming requests are valid against the schema. The path
definition is an OperationObject
with all of the information about the requests and responses on that route. It returns a middleware function which
can be used in an express app and will call `next(err) if the incoming request is invalid.
The error is created with (http-errors)[https://www.npmjs.com/package/http-errors], and then is augmented with
information about the schema and validation errors. Validation uses (avj)[https://www.npmjs.com/package/ajv],
and err.validationErrors is the format exposed by that package.
Example:
app.get('/:foo', oapi.validPath({
description: 'Get a foo',
responses: {
200: {
content: {
'application/json': {
schema: {
type: 'object',
properties: {
foo: { type: 'string' }
}
}
}
}
},
400: {
content: {
'application/json': {
schema: {
type: 'object',
properties: {
error: { type: 'string' }
}
}
}
}
}
}
}), (err, req, res, next) => {
res.status(err.status).json({
error: err.message,
validation: err.validationErrors,
schema: err.validationSchema
})
})OpenApiMiddleware.component(type[, name[, definition]])
Defines a new Component
on the document.
Example:
oapi.component('examples', 'FooExample', {
summary: 'An example of foo',
value: 'bar'
})If neither definition nor name are passed, the function will return the full components json.
Example:
oapi.component('examples', FooExample)
// { '$ref': '#/components/examples/FooExample' }If name is defined but definition is not, it will return a
Reference Object
pointing to the component by that name.
Example:
oapi.component('examples')
// { summary: 'An example of foo', value: 'bar' }OpenApiMiddleware.schema(name[, definition])
OpenApiMiddleware.response(name[, definition])
OpenApiMiddleware.parameters(name[, definition])
OpenApiMiddleware.examples(name[, definition])
OpenApiMiddleware.requestBodies(name[, definition])
OpenApiMiddleware.headers(name[, definition])
OpenApiMiddleware.securitySchemes(name[, definition])
OpenApiMiddleware.links(name[, definition])
OpenApiMiddleware.callbacks(name[, definition])
There are special component middleware for all of the types of component defined in the
OpenAPI spec.
Each of which is just the component method with a bound type, and behave with the same variadic behavior.
OpenApiMiddleware.redoc()
OpenApiMiddleware.swaggerui()
Serve an interactive UI for exploring the OpenAPI document.
Redoc and SwaggerUI are two of the most popular tools for viewing OpenAPI documents and are bundled with the middleware. They are not turned on by default but can be with the option mentioned above or by using one of these middleware.
Example:
app.use('/redoc', oapi.redoc)
app.use('/swaggerui', oapi.swaggerui)
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