Express middleware to validate requests based on an OpenAPI 3.0 document. OpenAPI specification was called the Swagger specification before version 3.

Install this package with npm or yarn:

npm install --save express-openapi-validate
# or
yarn add express-openapi-validate

Then use the validator like this:

const fs = require("fs");
const express = require("express");
const { OpenApiValidator } = require("express-openapi-validate");
const jsYaml = require("js-yaml");

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

const openApiDocument = jsYaml.safeLoad(
  fs.readFileSync("openapi.yaml", "utf-8"),
);
const validator = new OpenApiValidator(openApiDocument);

app.post("/echo", validator.validate("post", "/echo"), (req, res, next) => {
  res.json({ output: req.body.input });
});

app.use((err, req, res, next) => {
  const statusCode = err.statusCode || 500;
  res.status(statusCode).json({
    error: {
      name: err.name,
      message: err.message,
      data: err.data,
    },
  });
});

const server = app.listen(3000, () => {
  console.log("Listening on", server.address());
});

openapi: 3.0.1
info:
  title: Example API with a single echo endpoint
  version: 1.0.0
components:
  schemas:
    Error:
      type: object
      properties:
        error:
          type: object
          properties:
            name:
              type: string
            message:
              type: string
            data:
              type: array
              items:
                type: object
          required:
            - name
            - message
      required:
        - error
  responses:
    error:
      description: Default error response with error object
      content:
        application/json:
          schema:
            $ref: "#/components/schemas/Error"
paths:
  /echo:
    post:
      description: Echo input back
      requestBody:
        content:
          application/json:
            schema:
              type: object
              properties:
                input:
                  type: string
              required:
                - input
      responses:
        "200":
          description: Echoed input
          content:
            application/json:
              schema:
                type: object
                properties:
                  output:
                    type: string
        default:
          $ref: "#/components/responses/error"

• Validating request bodies with a schema (See Request Body Object and Schema Object)
  • All schema properties in a Schema Object that are directly supported by JSON Schema and Ajv are used in validation
  • Schemas are validated according to JSON Schema Specification Wright Draft 00 (draft-04/05) as specified in OpenAPI specification
  • nullable field for handling properties that can be null is supported (See OpenAPI fixed fields)
  • Validation according to format including additional data type formats (like int32 and bytes) defined by OpenAPI (See OpenAPI data types and Ajv formats)
• Validating parameters: query, header, path and cookies (including signed cookies) (See Parameter Object)
  • The same schema features that are supported for request bodies are also supported for parameters
  • required field for marking parameters that must be given is supported
• Validating response bodies and headers in tests (See Responses Object and Header Object)
• References to Components Object (See Reference Object)
• Typescript definitions are included in the package

• Validating request bodies with media type other than application/json (See content under Request Body Object)
• Some OpenAPI Schema Object specific fields are unsupported:
  • deprecated
  • discriminator
  • xml
• External references (references to other files and network resources) (See Reference Object)
• Parameter Objects (including Header Objects) that define shape using content and style (only schema is supported)
• Links and callbacks (See Callback Object and Link Object)
• Encodings (See Encoding Object)

const { OpenApiValidator } = require("express-openapi-validate");

The main class of this package. Creates JSON schema validators for the given operations defined in the OpenAPI document. In the background Ajv is used to validate the request.

Creates a new validator for the given OpenAPI document.

options parameter is optional. It has the following optional fields:

{
  ajvOptions: Ajv.Options;
}

You can find the list of options accepted by Ajv from its documentation. The formats object passed to Ajv will be merged with additional OpenAPI formats supported by this library.

Returns an express middleware function for the given operation. The operation matching the given method and path has to be defined in the OpenAPI document or this method throws.

The middleware validates the incoming request according to the parameters and requestBody fields defined in the Operation Object. If the validation fails the next express function is called with an ValidationError.

See the Parameter Object and Request Body Object sections of the OpenAPI specification for details how to define schemas for operations.

method must be one of the valid operations of an OpenAPI Path Item Object: "get" | "put" | "post" | "delete" | "options" | "head" | "patch" | "trace".

RequestHandler is an express middleware function with the signature (req: Request, res: Response, next: NextFunction): any;.

Creates a function for the given operation that can be used to validate responses. Response validation is meant to be used in tests and not in production code. See below for example usage.

For documentation of the method and path parameters see validate.

res is expected to have the shape { statusCode: number, body: {}, headers: {}}. The statusCode field can also be called status and the body field can be called data. This means that response objects from most request libraries should work out of the box.

If validation fails the validation function throws a ValidationError. Otherwise it returns undefined.

Example usage when using Jest and SuperTest:

import { OpenApiValidator } from "express-openapi-validate";
import fs from "fs";
import jsYaml from "js-yaml";
import request from "supertest";
import app from "./app";

const openApiDocument = jsYaml.safeLoad(
  fs.readFileSync("openapi.yaml", "utf-8"),
);
const validator = new OpenApiValidator(openApiDocument);

test("/echo responses", async () => {
  const validateResponse = validator.validateResponse("post", "/echo");
  let res = await request(app)
    .post("/echo")
    .send({});
  expect(validateResponse(res)).toBeUndefined();

  res = await request(app)
    .post("/echo")
    .send({ input: "Hello!" });
  expect(validateResponse(res)).toBeUndefined();
});

const { ValidationError } = require("express-openapi-validate");

This error is thrown by OpenApiValidator#validate when the request validation fails. It contains useful information about why the validation failed in human-readable format in the .message field and in machine-readable format in the .data array.

You can catch this error in your express error handler and handle it specially. You probably want to log the validation error and pass the errors to the client.

Human-readable error message about why the validation failed.

This field is always set to 400. You can check this field in your express error handler to decide what status code to send to the client when errors happen.

Machine-readable array of validation errors. Ajv Error Objects documentation contains a list of the fields in ErrorObject.