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 (json only)
- 👮 security validation / custom security functions
- 👽 3rd party / custom formats
- 🧵 optionally auto-map OpenAPI endpoints to Express handler functions
- ✂️ $ref support; split specs over multiple files
- 🎈 file upload
npm install express-openapi-validator- Require/import the openapi validator
const OpenApiValidator = require('express-openapi-validator');- Install the middleware
app.use(
OpenApiValidator.middleware({
apiSpec: './openapi.yaml',
validateRequests: true, // (default)
validateResponses: true, // false by default
}),
);- Register an error handler
app.use((err, req, res, next) => {
// format error
res.status(err.status || 500).json({
message: err.message,
errors: err.errors,
});
});Important: Ensure express is configured with all relevant body parsers. Body parser middleware functions must be specified prior to any validated routes. See an example.
In v4.x.x, the validator is installed as standard connect middleware using app.use(...) and/or router.use(...) (example). This differs from the v3.x.x the installation which required the install method(s). The install methods no longer exist in v4.
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 and OpenAPI spec for the example below:
const express = require('express');
const path = require('path');
const bodyParser = require('body-parser');
const http = require('http');
const app = express();
// 1. Import the express-openapi-validator library
const OpenApiValidator = require('express-openapi-validator');
// 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 }));
// 3. (optionally) Serve the OpenAPI spec
const spec = path.join(__dirname, 'api.yaml');
app.use('/spec', express.static(spec));
// 4. Install the OpenApiValidator onto your express app
app.use(
OpenApiValidator.middleware({
apiSpec: './api.yaml',
validateResponses: true, // <-- to validate responses
// unknownFormats: ['my-format'] // <-- to provide custom formats
}),
);
// 5. Define routes using Express
app.get('/v1/pets', function (req, res, next) {
res.json([
{ id: 1, type: 'cat', name: 'max' },
{ id: 2, type: 'cat', name: 'mini' },
]);
});
app.post('/v1/pets', function (req, res, next) {
res.json({ name: 'sparky', type: 'dog' });
});
app.get('/v1/pets/:id', function (req, res, next) {
res.json({ id: req.params.id, type: 'dog', 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
console.error(err); // dump error to console for debug
res.status(err.status || 500).json({
message: err.message,
errors: err.errors,
});
});
http.createServer(app).listen(3000);Don't want to manually map your OpenAPI endpoints to Express handler functions? express-openapi-validator can do it for you, automatically!
Use express-openapi-validator's OpenAPI x-eov-operation-* vendor extensions. See a full example with source code and an OpenAPI spec
Here's the gist
- First, specifiy the
operationHandlersoption to set the base directory that contains your operation handler files.
app.use(
OpenApiValidator.middleware({
apiSpec,
operationHandlers: path.join(__dirname),
}),
);- Next, use the
x-eov-operation-idOpenAPI vendor extension oroperationIdto specify the id of operation handler to invoke.
/ping:
get:
# operationId: ping
x-eov-operation-id: ping- Next, use the
x-eov-operation-handlerOpenAPI vendor extension to specify a path (relative tooperationHandlers) to the module that contains the handler for this operation.
/ping:
get:
x-eov-operation-id: ping
x-eov-operation-handler: routes/ping # no .js or .ts extension- Finally, create the express handler module e.g.
routes/ping.js
module.exports = {
// the express handler implementaiton for ping
ping: (req, res) => res.status(200).send('pong'),
};Note: A file may contain one or many handlers.
Below are some code snippets:
app.js
const express = require('express');
const path = require('path');
const bodyParser = require('body-parser');
const logger = require('morgan');
const http = require('http');
const OpenApiValidator = require('express-openapi-validator');
const port = 3000;
const app = express();
const apiSpec = path.join(__dirname, 'api.yaml');
// 1. Install bodyParsers for the request types your API will support
app.use(bodyParser.urlencoded({ extended: false }));
app.use(bodyParser.text());
app.use(bodyParser.json());
app.use(logger('dev'));
app.use('/spec', express.static(apiSpec));
// 2. Install the OpenApiValidator on your express app
app.use(
OpenApiValidator.middleware({
apiSpec,
validateResponses: true, // default false
// 3. Provide the base path to the operation handlers directory
operationHandlers: path.join(__dirname), // default false
}),
);
// 4. Woah sweet! With auto-wired operation handlers, I don't have to declare my routes!
// See api.yaml for x-eov-* vendor extensions
// 5. Create a custom error handler
app.use((err, req, res, next) => {
// format errors
res.status(err.status || 500).json({
message: err.message,
errors: err.errors,
});
});
http.createServer(app).listen(port);
console.log(`Listening on port ${port}`);
module.exports = app;api.yaml
/ping:
get:
description: |
ping then pong!
# OpenAPI's operationId may be used to to specify the operation id
operationId: ping
# x-eov-operation-id may be used to specify the operation id
# Used when operationId is omiited. Overrides operationId when both are specified
x-eov-operation-id: ping
# specifies the path to the operation handler.
# the path is relative to the operationHandlers option
# e.g. operations/base/path/routes/ping.js
x-eov-operation-handler: routes/ping
responses:
'200':
description: OK
# ...ping.js
module.exports = {
// ping must match operationId or x-eov-operation-id above
// note that x-eov-operation-id overrides operationId
ping: (req, res) => res.status(200).send('pong'),
};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 returns the following error codes depending on the situation.
| status | when |
|---|---|
400 (bad request) |
a validation error is encountered |
401 (unauthorized) |
a security / authentication errors is encountered e.g. missing api-key, Authorization header, etc |
404 (not found) |
a path is not found i.e. not declared in the API spec |
405 (method not allowed) |
a path is declared in the API spec, but a no schema is provided for the method |
| status | when |
|---|---|
500 (internal server error) |
any error is encountered by the validator |
express-openapi validator provides a good deal of flexibility via its options.
Options are provided via the options object. Options take the following form:
OpenApiValidator.middleware({
apiSpec: './openapi.yaml',
validateRequests: true,
validateResponses: true,
validateSecurity: {
handlers: {
ApiKeyAuth: (req, scopes, schema) => {
throw { status: 401, message: 'sorry' }
}
}
},
validateFormats: 'fast',
formats: [{
name: 'my-custom-format',
type: 'string' | 'number',
validate: (value: any) => boolean,
}],
unknownFormats: ['phone-number', 'uuid'],
operationHandlers: false | 'operations/base/path' | { ... },
ignorePaths: /.*\/pets$/,
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 optionsallowUnknownQueryParameters:
true- enables unknown/undeclared query parameters to pass validationfalse- (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 optionsremoveAdditional:
"failing"- additional properties that fail schema validation are automatically removed from the response.
coerceTypes:
true- coerce scalar data types.false- (default) do not coerce types. (almost always the desired behavior)"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).
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 withhandlers. 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 list of custome formats.
[{ ... }]- array of custom format objects. Each object must have the following properties:- name: string (required) - the format name
- validate: (v: any) => boolean (required) - the validation function
- type: 'string' | 'number' (optional) - the format's type
e.g.
formats: [
{
name: 'my-three-digit-format',
type: 'number',
// validate returns true the number has 3 digits, false otherwise
validate: (v) => /^\d{3}$/.test(v.toString()),
},
{
name: 'my-three-letter-format',
type: 'string',
// validate returns true the string has 3 letters, false otherwise
validate: (v) => /^[A-Za-z]{3}$/.test(v),
},
];Then use it in a spec e.g.
my_property:
type: string
format: my-three-letter-format'Specifies the strictness of validation of string formats.
"fast"(default) - only validate syntax, but not semantics. E.g.2010-13-30T23:12:35Zwill pass validation eventhough it contains month 13."full"- validate both syntax and semantics. Illegal dates will not pass.false- do not validate formats at all.
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.
Defines the base directory for operation handlers. This is used in conjunction with express-openapi-validator's OpenAPI vendor extensions, x-eov-operation-id, x-eov-operation-handler and OpenAPI's operationId. See example.
Additionally, if you want to change how modules are resolved e.g. use dot deliminted operation ids e.g. path.to.module.myFunction, you may optionally add a custom resolver. See documentation and example
-
string- the base directory containing operation handlers -
false- (default) disable auto wired operation handlers -
{ ... }- specifies a base directory and optionally a custom resolverhandlers:
For example:
operationHandlers: { basePath: __dirname, resolver: function (modulePath, route): express.RequestHandler { ///... } }
operationHandlers: 'operations/base/path'
Note that the x-eov-operation-handler OpenAPI vendor extension specifies a path relative to operationHandlers. Thus if operationHandlers is /handlers and an x-eov-operation-handler has path routes/ping, then the handler file /handlers/routes/ping.js (or ts) is used.
Complete example here
api.yaml
/ping:
get:
description: |
ping then pong!
# OpenAPI's operationId may be used to to specify the operation id
operationId: ping
# x-eov-operation-id may be used to specify the operation id
# Used when operationId is omiited. Overrides operationId when both are specified
x-eov-operation-id: ping
# specifies the path to the operation handler.
# the path is relative to the operationHandlers option
# e.g. operations/base/path/routes/ping.js
x-eov-operation-handler: routes/ping
responses:
'200':
description: OK
# ...routes/ping.js
x-eov-operation-handler specifies the path to this handlers file, ping.js
x-eov-operation-id (or operationId) specifies operation handler's key e.g. ping
module.exports = {
ping: (req, res) => res.status(200).send('pong'),
};Defines a regular expression or function that determines whether a path(s) should be ignored. If it's a regular expression, any path that matches the regular expression will be ignored by the validator. If it's a function, it will ignore any paths that returns a truthy value.
The following ignores any path that ends in /pets e.g. /v1/pets.
As a regular expression:
ignorePaths: /.*\/pets$/
or as a function:
ignorePaths: (path) => path.endsWith('/pets')
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 optionse.g.
fileUploader: { dest: 'uploads/'; }
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';
}Determines whether the validator should coerce value types to match the those defined in the OpenAPI spec. This option applies only to path params, query strings, headers, and cookies. It is highly unlikley that will want to disable this. As such this option is deprecated and will be removed in the next major version
true(default) - coerce scalar data types."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).
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/v1The validation applies to all paths defined under this base URL. Routes in your app that are _not_se URL—such as pages—will not be validated.
| URL | Validated? |
|---|---|
https://api.example.com/v1/users |
✅ |
https://api.example.com/index.html |
no; not under the base URL |
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
handlersare an optional component. securityhandlersprovide a convenience, whereby the request, declared scopes, and the security schema itself are provided as parameters to each securityhandlerscallback 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 securityhandlersprovide 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
handlersare 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
handlersis an object that maps security keys to security handler functions. Each security key must correspond tosecuritySchemename. ThevalidateSecurity.handlersobject signature is as follows:{ validateSecurity: { handlers: { [securityKey]: function( req: Express.Request, scopes: string[], schema: SecuritySchemeObject ): void, } } }
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:
throw { status: 403, message: 'forbidden' }throw Error('optional message')return false- return a promise which resolves to
falsee.gPromise.resolve(false) - 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-KeySee OpenAPI 3 authentication for securityScheme and security documentation
See examples from unit tests
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.
See complete example
const express = require('express');
const path = require('path');
const bodyParser = require('body-parser');
const http = require('http');
const OpenApiValidator = require('express-openapi-validator');
app = express();
app.use(bodyParser.urlencoded({ extended: false }));
app.use(bodyParser.text());
app.use(bodyParser.json());
const versions = [1, 2];
for (const v of versions) {
const apiSpec = path.join(__dirname, `api.v${v}.yaml`);
app.use(
OpenApiValidator.middleware({
apiSpec,
}),
);
routes(app, v);
}
http.createServer(app).listen(3000);
console.log('Listening on port 3000');
function routes(app, v) {
if (v === 1) routesV1(app);
if (v === 2) routesV2(app);
}
function routesV1(app) {
const v = '/v1';
app.post(`${v}/pets`, (req, res, next) => {
res.json({ ...req.body });
});
app.get(`${v}/pets`, (req, res, next) => {
res.json([
{
id: 1,
name: 'happy',
type: 'cat',
},
]);
});
app.use((err, req, res, next) => {
// format error
res.status(err.status || 500).json({
message: err.message,
errors: err.errors,
});
});
}
function routesV2(app) {
const v = '/v2';
app.get(`${v}/pets`, (req, res, next) => {
res.json([
{
pet_id: 1,
pet_name: 'happy',
pet_type: 'kitty',
},
]);
});
app.post(`${v}/pets`, (req, res, next) => {
res.json({ ...req.body });
});
app.use((err, req, res, next) => {
// format error
res.status(err.status || 500).json({
message: err.message,
errors: err.errors,
});
});
}
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: 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:
Q: I upgraded from from v2 to v3 and validation no longer works. How do I fix it?
A: 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.
Pet:
additionalProperties: false
required:
- name
properties:
name:
type: string
type:
type: stringQ: 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')
...
app.use('/', swaggerUi.serve, swaggerUi.setup(documentation))
app.use(OpenApiValidator.middleware({
apiSpec, // api spec JSON object
//... other options
}
}))Q: I have a handler function defined on an express.Router. If i call req.params each param value has type string. If i define same handler function on an express.Application, each value in req.params is already coerced to the type declare in my spec. Why not coerce theseF values on an express.Router?
A: First, it's important to note that this behavior does not impact validation. The validator will validate against the type defined in your spec.
In order to modify the req.params, express requires that a param handler be registered e.g. app.param(...) or router.param(...). Since app is available to middleware functions, the validator registers an app.param handler to coerce and modify the values of req.params to their declared types. Unfortunately, express does not provide a means to determine the current router from a middleware function, hence the validator is unable to register the same param handler on an express router. Ultimately, this means if your handler function is defined on app, the values of req.params will be coerced to their declared types. If your handler function is declare on an express.Router, the values of req.params values will be of type string (You must coerce them e.g. parseInt(req.params.id)).
Contributions welcome! Here's how to contribute.
Thanks goes to these wonderful people (emoji key):
This project follows the all-contributors specification. Contributions of any kind welcome!
Seeking content creators...
Have you written an article, blog, or tutorial that uses express-openapi-validator?
Please post your links here
We plan to publicize a variety of links here.
