An OpenApi validator for ExpressJS that automatically validates API requests and responses using an OpenAPI 3 specification.

🦋express-openapi-validator is an unopinionated library that integrates with new and existing API applications. express-openapi-validator lets you write code the way you want; it does not impose any coding convention or project layout. Simply, install the validator onto your express app, point it to your OpenAPI 3 specification, then define and implement routes the way you prefer. See an example.

Features:

• ✔️ request validation
• ✔️ response validation
• 👮 security validation / custom security functions
• 👽 3rd party / custom formats
• ✂️ $ref support; split specs over multiple files
• 🎈 file upload

npm i express-openapi-validator

In version 2.x.x, the install method was executed synchronously, in 3.x it's executed asynchronously. To get v2 behavior in v3, use the installSync method. See the synchronous section for details.

🦋express-openapi-validator may be used asynchronously (promises, async/await, callbacks) or synchronously. See a complete example

1. Install the openapi validator

await new OpenApiValidator({
  apiSpec: './test/resources/openapi.yaml',
  validateRequests: true, // (default)
  validateResponses: true, // false by default
}).install(app);

2. Register an error handler

app.use((err, req, res, next) => {
  // format error
  res.status(err.status || 500).json({
    message: err.message,
    errors: err.errors,
  });
});

Note: Ensure express is configured with all relevant body parsers. Body parser middleware functions must be specified prior to any validated routes. See an example.

See examples using promises and callbacks. Or use it synchronously

See Advanced Usage options to:

• inline api specs as JSON.
• configure request/response validation options
• customize authentication with security validation handlers.
• use OpenAPI 3.0.x 3rd party and custom formats.
• tweak the file upload configuration.
• ignore routes
• and more...

The following demonstrates how to use express-openapi-validator to auto validate requests and responses. It also includes file upload!

See the complete source code for the example below:

const express = require('express');
const path = require('path');
const cookieParser = require('cookie-parser');
const bodyParser = require('body-parser');
const logger = require('morgan');
const http = require('http');
const app = express();

// 1. Import the express-openapi-validator library
const OpenApiValidator = require('express-openapi-validator').OpenApiValidator;

// 2. Set up body parsers for the request body types you expect
//    Must be specified prior to endpoints in 5.
app.use(bodyParser.json());
app.use(bodyParser.text());
app.use(bodyParser.urlencoded({ extended: false }));

app.use(logger('dev'));
app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));

// 3. (optionally) Serve the OpenAPI spec
const spec = path.join(__dirname, 'example.yaml');
app.use('/spec', express.static(spec));

// 4. Install the OpenApiValidator onto your express app
new OpenApiValidator({
  apiSpec: './example.yaml',
  validateResponses: true, // <-- to validate responses
  // unknownFormats: ['my-format'] // <-- to provide custom formats
})
  .install(app)
  .then(() => {
    // 5. Define routes using Express
    app.get('/v1/pets', function(req, res, next) {
      res.json([
        { id: 1, name: 'max' },
        { id: 2, name: 'mini' },
      ]);
    });

    app.post('/v1/pets', function(req, res, next) {
      res.json({ name: 'sparky' });
    });

    app.get('/v1/pets/:id', function(req, res, next) {
      res.json({ id: req.params.id, name: 'sparky' });
    });

    // 5a. Define route(s) to upload file(s)
    app.post('/v1/pets/:id/photos', function(req, res, next) {
      // files are found in req.files
      // non-file multipart params can be found as such: req.body['my-param']

      res.json({
        files_metadata: req.files.map(f => ({
          originalname: f.originalname,
          encoding: f.encoding,
          mimetype: f.mimetype,
          // Buffer of file conents
          buffer: f.buffer,
        })),
      });
    });

    // 6. Create an Express error handler
    app.use((err, req, res, next) => {
      // 7. Customize errors
      res.status(err.status || 500).json({
        message: err.message,
        errors: err.errors,
      });
    });

    http.createServer(app).listen(3000);
  });

curl -s http://localhost:3000/v1/pets/as |jq
{
  "message": "request.params.id should be integer",
  "errors": [
    {
      "path": ".params.id",
      "message": "should be integer",
      "errorCode": "type.openapi.validation"
    }
  ]
}

 curl -s 'http://localhost:3000/v1/pets?limit=25' |jq
{
  "message": "request.query should have required property 'type', request.query.limit should be <= 20",
  "errors": [
    {
      "path": ".query.type",
      "message": "should have required property 'type'",
      "errorCode": "required.openapi.validation"
    },
    {
      "path": ".query.limit",
      "message": "should be <= 20",
      "errorCode": "maximum.openapi.validation"
    }
  ]
}

 curl -s --request POST \
  --url http://localhost:3000/v1/pets \
  --data '{}' |jq
{
  "message": "'X-API-Key' header required",
  "errors": [
    {
      "path": "/v1/pets",
      "message": "'X-API-Key' header required"
    }
  ]
}

Providing the header passes OpenAPI validation.

Note: that your Express middleware or endpoint logic can then provide additional checks.

curl -XPOST http://localhost:3000/v1/pets \
  --header 'X-Api-Key: XXXXX' \
  --header 'content-type: application/json' \
  -d '{"name": "spot"}' | jq

{
  "id": 4,
  "name": "spot"
}

curl -s --request POST \
  --url http://localhost:3000/v1/pets \
  --header 'content-type: application/xml' \
  --header 'x-api-key: XXXX' \
  --data '{
        "name": "test"
}' |jq
  "message": "unsupported media type application/xml",
  "errors": [
    {
      "path": "/v1/pets",
      "message": "unsupported media type application/xml"
    }
  ]
}

curl -s --request POST \
  --url http://localhost:3000/v1/pets \
  --header 'content-type: application/json' \
  --header 'x-api-key: XXXX' \
  --data '{}'|jq
{
  "message": "request.body should have required property 'name'",
  "errors": [
    {
      "path": ".body.name",
      "message": "should have required property 'name'",
      "errorCode": "required.openapi.validation"
    }
  ]
}

curl -XPOST http://localhost:3000/v1/pets/10/photos -F [email protected]|jq
{
  "files_metadata": [
    {
      "originalname": "app.js",
      "encoding": "7bit",
      "mimetype": "application/octet-stream"
    }
  ]
}

Errors in response validation return 500, not of 400

/v1/pets/99 will return a response that does not match the spec

 curl -s 'http://localhost:3000/v1/pets/99' |jq
{
  "message": ".response should have required property 'name', .response should have required property 'id'",
  "errors": [
    {
      "path": ".response.name",
      "message": "should have required property 'name'",
      "errorCode": "required.openapi.validation"
    },
    {
      "path": ".response.id",
      "message": "should have required property 'id'",
      "errorCode": "required.openapi.validation"
    }
  ]
}

express-openapi validator provides a good deal of flexibility via its options.

Options are provided via the options object. Options take the following form:

new OpenApiValidator(options).install({
  apiSpec: './openapi.yaml',
  validateRequests: true,
  validateResponses: true,
  validateSecurity: {
    handlers: {
      ApiKeyAuth: (req, scopes, schema) => {
        throw { status: 401, message: 'sorry' }
      }
    }
  },
  ignorePaths: /.*\/pets$/,
  unknownFormats: ['phone-number', 'uuid'],
  fileUploader: { ... } | true | false,
  $refParser: {
    mode: 'bundle'
  }
});

Specifies the path to an OpenAPI 3 specification or a JSON object representing the OpenAPI 3 specificiation

apiSpec: './path/to/my-openapi-spec.yaml';

or

  apiSpec: {
  openapi: '3.0.1',
  info: {...},
  servers: [...],
  paths: {...},
  components: {
    responses: {...},
    schemas: {...}
  }
}

Determines whether the validator should validate requests.

• true (default) - validate requests.

• false - do not validate requests.

• { ... } - validate requests with options

  allowUnknownQueryParameters:

  • true - enables unknown/undeclared query parameters to pass validation
  • false - (default) fail validation if an unknown query parameter is present

  For example:

  validateRequests: {
    allowUnknownQueryParameters: true;
  }

Determines whether the validator should validate responses. Also accepts response validation options.

• true - validate responses in 'strict' mode i.e. responses MUST match the schema.

• false (default) - do not validate responses

• { ... } - validate responses with options

  removeAdditional:

  • "failing" - additional properties that fail schema validation are automatically removed from the response.

  For example:

  validateResponses: {
    removeAdditional: 'failing'
  }

Determines whether the validator should validate securities e.g. apikey, basic, oauth2, openid, etc

• true (default) - validate security

• false - do not validate security

• { ... } - validate security with handlers. See Security handlers doc.

  handlers:

  For example:

  validateSecurity: {
    handlers: {
      ApiKeyAuth: function(req, scopes, schema) {
        console.log('apikey handler throws custom error', scopes, schema);
        throw Error('my message');
      },
    }
  }

Defines a regular expression that determines whether a path(s) under the base url should be ignored. Any path which matches the regular expression will not be validated.

The following ignores any path that ends in /pets

ignorePaths: /.*\/pets$/

Defines how the validator should behave if an unknown or custom format is encountered.

• true (default) - When an unknown format is encountered, the validator will report a 400 error.

• [string] (recommended for unknown formats) - An array of unknown format names that will be ignored by the validator. This option can be used to allow usage of third party schemas with format(s), but still fail if another unknown format is used. e.g.

  unknownFormats: ['phone-number', 'uuid'];

• "ignore" - to log warning during schema compilation and always pass validation. This option is not recommended, as it allows to mistype format name and it won't be validated without any error message.

Specifies the options to passthrough to multer. express-openapi-validator uses multer to handle file uploads. see multer opts

• true (default) - enables multer and provides simple file(s) upload capabilities

• false - disables file upload capability. Upload capabilities may be provided by the user

• {...} - multer options to be passed-through to multer. see multer opts for possible options

  e.g.

  fileUploader: {
    dest: 'uploads/';
  }

Determines whether the validator should coerce value types to match the type defined in the OpenAPI spec.

• true (default) - coerce scalar data types.
• false - no type coercion.
• "array" - in addition to coercions between scalar types, coerce scalar data to an array with one element and vice versa (as required by the schema).

Determines how JSON schema references are resolved by the internal json-schema-ref-parser. Generally, the default mode, bundle is sufficient, however if you use escape characters in $refs, dereference is necessary.

• bundle (default) - Bundles all referenced files/URLs into a single schema that only has internal $ref pointers. This eliminates the risk of circular references, but does not handle escaped characters in $refs.
• dereference - Dereferences all $ref pointers in the JSON Schema, replacing each reference with its resolved value. Introduces risk of circular $refs. Handles escape characters in $refs)

See this issue for more information.

e.g.

$refParser: {
  mode: 'bundle'
}

The validator will only validate requests, securities, and responses that are under the server's base URL.

This is useful for those times when the API and frontend are being served by the same application. (More detail about the base URL.)

servers:
- url: https://api.example.com/v1

The validation applies to all paths defined under this base URL. Routes in your app that are not under the base URL—such as pages—will not be validated.

In some cases, it may be necessary to skip validation for paths under the base url. To do this, use the ignorePaths option.

Note: security handlers are an optional component. security handlers provide a convenience, whereby the request, declared scopes, and the security schema itself are provided as parameters to each security handlers callback that you define. The code you write in each callback can then perform authentication and authorization checks. Note that the same can be achieved using standard Express middleware. The difference is that security handlers provide you the OpenAPI schema data described in your specification_. Ulimately, this means, you don't have to duplicate that information in your code.

All in all, security handlers are purely optional and are provided as a convenience.

Security handlers specify a set of custom security handlers to be used to validate security i.e. authentication and authorization. If a security handlers object is specified, a handler must be defined for all securities. If security `handlers are not specified, a default handler is always used. The default handler will validate against the OpenAPI spec, then call the next middleware.

If security handlers are specified, the validator will validate against the OpenAPI spec, then call the security handler providing it the Express request, the security scopes, and the security schema object.

• security handlers is an object that maps security keys to security handler functions. Each security key must correspond to securityScheme name. The validateSecurity.handlers object signature is as follows:

  {
    validateSecurity: {
      handlers: {
        [securityKey]: function(
          req: Express.Request,
          scopes: string[],
          schema: SecuritySchemeObject
        ): void,
      }
    }
  }

  SecuritySchemeObject

  For example:

  validateSecurity: {
    handlers: {
      ApiKeyAuth: function(req, scopes, schema) {
        console.log('apikey handler throws custom error', scopes, schema);
        throw Error('my message');
      },
    }
  }

The express-openapi-validator performs a basic validation pass prior to delegating to security handlers. If basic validation passes, security handler function(s) are invoked.

In order to signal an auth failure, the security handler function must either:

1. throw { status: 403, message: 'forbidden' }
2. throw Error('optional message')
3. return false
4. return a promise which resolves to false e.g Promise.resolve(false)
5. return a promise rejection e.g.
   • Promise.reject({ status: 401, message: 'yikes' });
   • Promise.reject(Error('optional 'message')
   • Promise.reject(false)

Note: error status 401 is returned, unless option i. above is used

Some examples:

validateSecurity: {
  handlers: {
    ApiKeyAuth: (req, scopes, schema) => {
      throw Error('my message');
    },
    OpenID: async (req, scopes, schema) => {
      throw { status: 403, message: 'forbidden' }
    },
    BasicAuth: (req, scopes, schema) => {
      return Promise.resolve(false);
    },
    ...
  }
}

In order to grant authz, the handler function must either:

• return true
• return a promise which resolves to true

Some examples

validateSecurity: {
  handlers: {
    ApiKeyAuth: (req, scopes, schema) => {
      return true;
    },
    BearerAuth: async (req, scopes, schema) => {
      return true;
    },
    ...
  }
}

Each security handlers' securityKey must match a components/securitySchemes property

components:
  securitySchemes:
    ApiKeyAuth: # <-- Note this name must be used as the name handler function property
      type: apiKey
      in: header
      name: X-API-Key

See OpenAPI 3 authentication for securityScheme and security documentation See examples from unit tests

In addition to async/await, express-openapi-validator may be used with promises, callbacks, or synchronously.

Note: Ensure express is configured with all relevant body parsers. Body parser middleware functions must be specified prior to any validated routes. See an example.

new OpenApiValidator({
  apiSpec: './test/resources/openapi.yaml',
  validateRequests: true, // (default)
  validateResponses: true, // false by default
})
  .install(app)
  .then(app => {
    // define your routes

    // register an error handler
    app.use((err, req, res, next) => {
      res.status(err.status || 500).json({
        message: err.message,
        errors: err.errors,
      });
    });
  });

new OpenApiValidator({
  apiSpec: './test/resources/openapi.yaml',
  validateRequests: true, // (default)
  validateResponses: true, // false by default
}).install(app, (err, _) => {
  // define your routes

  // register an error handler
  app.use((err, req, res, next) => {
    res.status(err.status || 500).json({
      message: err.message,
      errors: err.errors,
    });
  });
});

Note syncrhonous mode makes use of the deasync module. Some users have experienced issues using deasync with some versions of node

Q: What does it mean to use the validator 'synchronously'?

A: The installation of the validator is handled synchronously; this includes the initial parse and $ref resolution of the OpenAPI 3 spec. Note that all validation is executed asynchronously i.e. request, response, and security validation. Use installSync(app) instead of install(app) to install the validator in a blocking manner.

1. Install the openapi validator

new OpenApiValidator({
  apiSpec: './test/resources/openapi.yaml',
  validateRequests: true, // (default)
  validateResponses: true, // false by default
}).installSync(app);

2. Register an error handler

app.use((err, req, res, next) => {
  // format error
  res.status(err.status || 500).json({
    message: err.message,
    errors: err.errors,
  });
});

It may be useful to serve multiple APIs with separate specs via single service. An exampe might be an API that serves both v1 and v2 from the samee service. The sample code below show how one might accomplish this.

const express = require('express');
const path = require('path');
const bodyParser = require('body-parser');
const http = require('http');
const { OpenApiValidator } = require('express-openapi-validator');

async function main() {
  app = express();
  app.use(bodyParser.urlencoded({ extended: false }));
  app.use(bodyParser.text());
  app.use(bodyParser.json());
  app.use(express.static(path.join(__dirname, 'public')));

  const versions = [1, 2];

  for (let v of versions) {
    let apiSpec = path.join(__dirname, `v${v}.yaml`);
    await new OpenApiValidator({
      apiSpec,
    }).install(app);

    routes(app, v++);
  }

  http.createServer(app).listen(3000);
  console.log('Listening on port 3000');
}

async function routes(app, v) {
  if (v === 1) routesV1(app);
  if (v === 2) routesV2(app);
}

async function routesV1(app) {
  const v = '/api/v1';
  app.post(`${v}/annotations`, (req, res, next) => {
    res.json({ ...req.body, annotations: v, method: 'post' });
  });

  app.use((err, req, res, next) => {
    // format error
    res.status(err.status || 500).json({
      message: err.message,
      errors: err.errors,
    });
  });
}

async function routesV2(app) {
  const v = '/api/v2';
  app.post(`${v}/annotations`, (req, res, next) => {
    res.json({ ...req.body, annotations: v, method: 'post' });
  });

  app.use((err, req, res, next) => {
    // format error
    res.status(err.status || 500).json({
      message: err.message,
      errors: err.errors,
    });
  });
}

main();
module.exports = app;

Q: What happened to the securityHandlers property?

A: In v3, securityHandlers have been replaced by validateSecurity.handlers. To use v3 security handlers, move your existing security handlers to the new property. No other change is required. Note that the v2 securityHandlers property is supported in v3, but deprecated

Q: What happened to the multerOpts property?

A: In v3, multerOpts have been replaced by fileUploader. In order to use the v3 fileUploader, move your multer options to fileUploader No other change is required. Note that the v2 multerOpts property is supported in v3, but deprecated

Q: Can I use a top level await?

A: Top-level await is currently a stage 3 proposal, however it can be used today with babel

Q: I can disallow unknown query parameters with allowUnknownQueryParameters: false. How can disallow unknown body parameters?

A: Add additionalProperties: false when describing e.g a requestBody to ensure that additional properties are not allowed. For example:

Pet:
additionalProperties: false
required:
  - name
properties:
  name:
    type: string
  type:
    type: string

Q: Can I use express-openapi-validator with swagger-ui-express?

A: Yes. Be sure to use the swagger-ui-express serve middleware prior to installing OpenApiValidator. This will ensure that swagger-ui-express is able to fully prepare the spec before before OpenApiValidator attempts to use it. For example:

const swaggerUi = require('swagger-ui-express')
const OpenApiValidator = require('express-openapi-validator').OpenApiValidator

...

app.use('/', swaggerUi.serve, swaggerUi.setup(documentation))

new OpenApiValidator({
  apiSpec, // api spec JSON object
  //... other options
  }
}).install(app)

Q: I see deasync is installed as a dependency. How is deasync used?

A: Although deasync is installed, it is dynamically loaded if and only if you explicitly call validator.installSync(app). If you don't, it will not be loaded or used.

Contributions welcome! Here's how to contribute.

Thanks goes to these wonderful people (emoji key):

Carmine DiMascio 💻 ⚠️ 🚇	Sheldhur Mornor 💻 ⚠️	Andrey Trebler 💻 ⚠️	richdouglasevans 📖	Miran Setinc 💻	Frank Calise 💻	Gonen Dukas 🤔 ⚠️
Sven Eliasson 💻 ⚠️	Spencer Brown 💻 ⚠️	José Neves 💻	mk811 💻 ⚠️	HugoMario 💻 ⚠️	Rowan Cockett 💻	Jacques Yakoub 💻
ckeboss 💻 ⚠️	JacobLey 💻 ⚠️

This project follows the all-contributors specification. Contributions of any kind welcome!

MIT