Express Zod API
Start your API server with I/O schema validation and custom middlewares in minutes.
- Why and what is it for
- How it works
- Quick start โ Fast Track
- Charming features
- Cross-Origin Resource Sharing (CORS)
- Middlewares
- Options
- Refinements
- Transformations
- Dealing with dates
- Route path params
- Response customization
- Non-object response including file downloads
- Array response for migrating legacy APIs
- Using native express middlewares
- File uploads
- Customizing logger
- Connect to your own express app
- Multiple schemas for one route
- Serving static files
- Customizing input sources
- Enabling compression
- Enabling HTTPS
- Generating a Frontend Client
- Creating a documentation
- Tagging the endpoints
- How to test endpoints
- Caveats
- Your input to my output
You can find the release notes and migration guides in Changelog.
Why and what is it for
I made this library because of the often repetitive tasks of starting a web server APIs with the need to validate input data. It integrates and provides the capabilities of popular web server, logger, validation and documenting solutions. Therefore, many basic tasks can be accomplished faster and easier, in particular:
- You can describe web server routes as a hierarchical object.
- You can keep the endpoint's input and output type declarations right next to its handler.
- All input and output data types are validated, so it ensures you won't have an empty string, null or undefined where you expect a number.
- Variables within an endpoint handler have types according to the declared schema, so your IDE and Typescript will provide you with necessary hints to focus on bringing your vision to life.
- All of your endpoints can respond in a consistent way.
- The expected endpoint input and response types can be exported to the frontend, so you don't get confused about the field names when you implement the client for your API.
- You can generate your API documentation in a Swagger / OpenAPI compatible format.
How it works
Technologies
- Typescript first.
- Web server โ Express.js.
- Schema validation โ Zod 3.x.
- Logger โ Winston.
- Generators:
- Documentation โ OpenAPI 3.x (Swagger Specification).
- Client side types โ inspired by zod-to-ts.
- File uploads โ Express-FileUpload (based on Busboy).
Concept
The API operates object schemas for input and output validation.
The object being validated is the combination of certain request properties.
It is available to the endpoint handler as the input parameter.
Middlewares have access to all request properties, they can provide endpoints with options.
The object returned by the endpoint handler is called output. It goes to the ResultHandler which is
responsible for transmitting consistent responses containing the output or possible error.
Much can be customized to fit your needs.
Quick start
Installation
Run one of the following commands to install the library and its peer dependencies. Typescript is an optional dependency, however, it's required if you're going to generate a frontend client for your API.
yarn add express-zod-api express zod winston typescript
# or
npm install express-zod-api express zod winston typescriptAdd the following option to your tsconfig.json file in order to make it work as expected:
{
"compilerOptions": {
"strict": true
}
}Set up config
import { createConfig } from "express-zod-api";
const config = createConfig({
server: {
listen: 8090, // port or socket
},
cors: true,
logger: {
level: "debug",
color: true,
},
});See all available options here.
Create an endpoints factory
In the basic case, you can just import and use the default factory:
import { defaultEndpointsFactory } from "express-zod-api";In case you need a global middleware, see Middlewares. In case you need to customize the response, see Response customization.
Create your first endpoint
import { z } from "zod";
const helloWorldEndpoint = defaultEndpointsFactory.build({
method: "get",
input: z.object({
// for empty input use z.object({})
name: z.string().optional(),
}),
output: z.object({
greetings: z.string(),
}),
handler: async ({ input: { name }, options, logger }) => {
logger.debug("Options:", options); // middlewares provide options
return { greetings: `Hello, ${name || "World"}. Happy coding!` };
},
});In case you want it to handle multiple methods use methods property instead of method.
Set up routing
Connect your endpoint to the /v1/hello route:
import { Routing } from "express-zod-api";
const routing: Routing = {
v1: {
hello: helloWorldEndpoint,
},
};Start your server
import { createServer } from "express-zod-api";
createServer(config, routing);You can disable startup logo using startupLogo entry of your config.
See the full implementation example here.
Try it
Execute the following command:
curl -L -X GET 'localhost:8090/v1/hello?name=Rick'You should receive the following response:
{ "status": "success", "data": { "greetings": "Hello, Rick. Happy coding!" } }Charming features
Cross-Origin Resource Sharing
You can enable your API for other domains using the corresponding configuration option cors.
It's not optional to draw your attention to making the appropriate decision, however, it's enabled in the
Quick start example above, assuming that in most cases you will want to enable this feature.
See MDN article for more information.
In addition to being a boolean, cors can also be assigned a function that provides custom headers. That function
has several parameters and can be asynchronous.
import { createConfig } from "express-zod-api";
const config = createConfig({
// ... other options
cors: ({ defaultHeaders, request, endpoint, logger }) => ({
...defaultHeaders,
"Access-Control-Max-Age": "5000",
}),
});Please note: If you only want to send specific headers on requests to a specific endpoint, consider the Middlewares or response customization approach.
Middlewares
Middleware can authenticate using input or request headers, and can provide endpoint handlers with options.
Inputs of middlewares are also available to endpoint handlers within input.
Here is an example on how to provide headers of the request.
import { createMiddleware } from "express-zod-api";
const headersProviderMiddleware = createMiddleware({
input: z.object({}), // means no inputs
middleware: async ({ request }) => ({
headers: request.headers,
}),
});By using .addMiddleware() method before .build() you can connect it to the endpoint:
const yourEndpoint = defaultEndpointsFactory
.addMiddleware(headersProviderMiddleware)
.build({
// ...,
handler: async ({ options }) => {
// options.headers === request.headers
},
});Here is an example of the authentication middleware, that checks a key from input and token from headers:
import { z } from "zod";
import { createMiddleware, createHttpError } from "express-zod-api";
const authMiddleware = createMiddleware({
security: {
// this information is optional and used for generating documentation
and: [
{ type: "input", name: "key" },
{ type: "header", name: "token" },
],
},
input: z.object({
key: z.string().min(1),
}),
middleware: async ({ input: { key }, request, logger }) => {
logger.debug("Checking the key and token");
const user = await db.Users.findOne({ key });
if (!user) {
throw createHttpError(401, "Invalid key");
}
if (request.headers.token !== user.token) {
throw createHttpError(401, "Invalid token");
}
return { user }; // provides endpoints with options.user
},
});You can connect the middleware to endpoints factory right away, making it kind of global:
import { defaultEndpointsFactory } from "express-zod-api";
const endpointsFactory = defaultEndpointsFactory.addMiddleware(authMiddleware);You can connect as many middlewares as you want, they will be executed in order.
Options
In case you'd like to provide your endpoints with options that do not depend on Request, like database connection
instance, consider shorthand method addOptions.
import { defaultEndpointsFactory } from "express-zod-api";
const endpointsFactory = defaultEndpointsFactory.addOptions({
db: mongoose.connect("mongodb://connection.string"),
privateKey: fs.readFileSync("private-key.pem", "utf-8"),
});Refinements
You can implement additional validations within schemas using refinements.
Validation errors are reported in a response with a status code 400.
import { z } from "zod";
import { createMiddleware } from "express-zod-api";
const nicknameConstraintMiddleware = createMiddleware({
input: z.object({
nickname: z
.string()
.min(1)
.refine(
(nick) => !/^\d.*$/.test(nick),
"Nickname cannot start with a digit",
),
}),
// ...,
});By the way, you can also refine the whole I/O object, for example in case you need a complex validation of its props.
const endpoint = endpointsFactory.build({
input: z
.object({
email: z.string().email().optional(),
id: z.string().optional(),
otherThing: z.string().optional(),
})
.refine(
(inputs) => Object.keys(inputs).length >= 1,
"Please provide at least one property",
),
// ...,
});Transformations
Since parameters of GET requests come in the form of strings, there is often a need to transform them into numbers or arrays of numbers.
import { z } from "zod";
const getUserEndpoint = endpointsFactory.build({
method: "get",
input: z.object({
id: z.string().transform((id) => parseInt(id, 10)),
ids: z
.string()
.transform((ids) => ids.split(",").map((id) => parseInt(id, 10))),
}),
output: z.object({
/* ... */
}),
handler: async ({ input: { id, ids }, logger }) => {
logger.debug("id", id); // type: number
logger.debug("ids", ids); // type: number[]
},
});Dealing with dates
Dates in Javascript are one of the most troublesome entities. In addition, Date cannot be passed directly in JSON
format. Therefore, attempting to return Date from the endpoint handler results in it being converted to an ISO string
in actual response by calling
toJSON(),
which in turn calls
toISOString().
It is also impossible to transmit the Date in its original form to your endpoints within JSON. Therefore, there is
confusion with original method z.date() that should not be used within IO schemas of your API.
In order to solve this problem, the library provides two custom methods for dealing with dates: ez.dateIn() and
ez.dateOut() for using within input and output schemas accordingly.
ez.dateIn() is a transforming schema that accepts an ISO string representation of a Date, validates it, and
provides your endpoint handler or middleware with a Date. It supports the following formats:
2021-12-31T23:59:59.000Z
2021-12-31T23:59:59Z
2021-12-31T23:59:59
2021-12-31
ez.dateOut(), on the contrary, accepts a Date and provides ResultHanlder with a string representation in ISO
format for the response transmission. Consider the following simplified example for better understanding:
import { z } from "zod";
import { ez, defaultEndpointsFactory } from "express-zod-api";
const updateUserEndpoint = defaultEndpointsFactory.build({
method: "post",
input: z.object({
userId: z.string(),
birthday: ez.dateIn(), // string -> Date
}),
output: z.object({
createdAt: ez.dateOut(), // Date -> string
}),
handler: async ({ input }) => {
// input.birthday is Date
return {
// transmitted as "2022-01-22T00:00:00.000Z"
createdAt: new Date("2022-01-22"),
};
},
});Route path params
You can describe the route of the endpoint using parameters:
import { Routing } from "express-zod-api";
const routing: Routing = {
v1: {
user: {
// route path /v1/user/:id, where :id is the path param
":id": getUserEndpoint,
// use the empty string to represent /v1/user if needed:
// "": listAllUsersEndpoint,
},
},
};You then need to specify these parameters in the endpoint input schema in the usual way:
const getUserEndpoint = endpointsFactory.build({
method: "get",
input: z.object({
// id is the route path param, always string
id: z.string().transform((value) => parseInt(value, 10)),
// other inputs (in query):
withExtendedInformation: z.boolean().optional(),
}),
output: z.object({
/* ... */
}),
handler: async ({ input: { id } }) => {
// id is the route path param, number
},
});Response customization
ResultHandler is responsible for transmitting consistent responses containing the endpoint output or an error.
The defaultResultHandler sets the HTTP status code and ensures the following type of the response:
type DefaultResponse<OUT> =
| {
// Positive response
status: "success";
data: OUT;
}
| {
// or Negative response
status: "error";
error: {
message: string;
};
};You can create your own result handler by using this example as a template:
import { z } from "zod";
import {
createResultHandler,
IOSchema,
getStatusCodeFromError,
getMessageFromError,
} from "express-zod-api";
export const yourResultHandler = createResultHandler({
getPositiveResponse: (output: IOSchema) => ({
schema: z.object({ data: output }),
mimeType: "application/json", // optinal, or mimeTypes for array
}),
getNegativeResponse: () => z.object({ error: z.string() }),
handler: ({ error, input, output, request, response, logger }) => {
if (!error) {
// your implementation
return;
}
const statusCode = getStatusCodeFromError(error);
const message = getMessageFromError(error);
// your implementation
},
});Note: OutputValidationError and InputValidationError are also available for your custom error handling.
After creating your custom ResultHandler you can use it as an argument for EndpointsFactory instance creation:
import { EndpointsFactory } from "express-zod-api";
const endpointsFactory = new EndpointsFactory(yourResultHandler);Please note: ResultHandler must handle any errors and not throw its own. Otherwise, the case will be passed to the
LastResortHandler, which will set the status code to 500 and send the error message as plain text.
Non-object response
Thus, you can configure non-object responses too, for example, to send an image file.
You can find two approaches to EndpointsFactory and ResultHandler implementation
in this example.
One of them implements file streaming, in this case the endpoint just has to provide the filename.
The response schema generally may be just z.string(), but I made more specific ez.file() that also supports
.binary() and .base64() refinements which are reflected in the
generated documentation.
const fileStreamingEndpointsFactory = new EndpointsFactory(
createResultHandler({
getPositiveResponse: () => ({
schema: ez.file().binary(),
mimeType: "image/*",
}),
getNegativeResponse: () => ({ schema: z.string(), mimeType: "text/plain" }),
handler: ({ response, error, output }) => {
if (error) {
response.status(400).send(error.message);
return;
}
if ("filename" in output) {
fs.createReadStream(output.filename).pipe(
response.type(output.filename),
);
} else {
response.status(400).send("Filename is missing");
}
},
}),
);Array response
Please avoid doing this in new projects: responding with array is a bad practice keeping your endpoints from evolving
in backward compatible way (without making breaking changes). Nevertheless, for the purpose of easier migration of
legacy APIs to this library consider using arrayResultHandler or arrayEndpointsFactory instead of default ones,
or implement your own ones in a similar way.
The arrayResultHandler expects your endpoint to have items property in the output object schema. The array
assigned to that property is used as the response. This approach also supports examples, as well as documentation and
client generation. Check out the example endpoint for more details.
Using native express middlewares
You can connect any native express middleware that can be supplied to express method app.use().
For this purpose the EndpointsFactory provides method addExpressMiddleware() and its alias use().
There are also two optional features available: a provider of options and an error transformer for ResultHandler.
In case the error in middleware is not a HttpError, the ResultHandler will send the status 500.
import { defaultEndpointsFactory, createHttpError } from "express-zod-api";
import cors from "cors";
import { auth } from "express-oauth2-jwt-bearer";
const simpleUsage = defaultEndpointsFactory.addExpressMiddleware(
cors({ credentials: true }),
);
const advancedUsage = defaultEndpointsFactory.use(auth(), {
provider: (req) => ({ auth: req.auth }), // optional, can be async
transformer: (err) => createHttpError(401, err.message), // optional
});File uploads
You can switch the Endpoint to handle requests with the multipart/form-data content type instead of JSON by using
ez.upload() schema. Together with a corresponding configuration option, this makes it possible to handle file uploads.
Here is a simplified example:
import { z } from "zod";
import { createConfig, ez, defaultEndpointsFactory } from "express-zod-api";
const config = createConfig({
server: {
upload: true, // <- required
// ...,
},
});
const fileUploadEndpoint = defaultEndpointsFactory.build({
method: "post",
input: z.object({
avatar: ez.upload(), // <--
}),
output: z.object({
/* ... */
}),
handler: async ({ input: { avatar } }) => {
// avatar: {name, mv(), mimetype, data, size, etc}
// avatar.truncated is true on failure
},
});You can still send other data and specify additional input parameters, including arrays and objects.
Customizing logger
You can specify your custom Winston logger in config:
import winston from "winston";
import { createConfig } from "express-zod-api";
const logger = winston.createLogger({
/* ... */
});
const config = createConfig({ logger /* ..., */ });Connect to your own express app
If you already have your own configured express application, or you find the library settings not enough,
you can connect your routing to the app instead of using createServer().
import express from "express";
import { createConfig, attachRouting } from "express-zod-api";
const app = express();
const config = createConfig({ app /* cors, logger, ... */ });
const routing = {
/* ... */
};
const { notFoundHandler, logger } = attachRouting(config, routing);
app.use(notFoundHandler); // optional
app.listen();
logger.info("Glory to science!");Please note that in this case you probably need to parse request.body, call app.listen() and handle 404
errors yourself. In this regard attachRouting() provides you with notFoundHandler which you can optionally connect
to your custom express app.
Multiple schemas for one route
Thanks to the DependsOnMethod class a route may have multiple Endpoints attached depending on different methods.
It can also be the same Endpoint that handles multiple methods as well.
import { DependsOnMethod } from "express-zod-api";
// the route /v1/user has two Endpoints
// which handle a couple of methods each
const routing: Routing = {
v1: {
user: new DependsOnMethod({
get: yourEndpointA,
delete: yourEndpointA,
post: yourEndpointB,
patch: yourEndpointB,
}),
},
};Serving static files
In case you want your server to serve static files, you can use new ServeStatic() in Routing using the arguments
similar to express.static().
The documentation on these arguments you may find here.
import { Routing, ServeStatic } from "express-zod-api";
import { join } from "node:path";
const routing: Routing = {
// path /public serves static files from ./assets
public: new ServeStatic(join(__dirname, "assets"), {
dotfiles: "deny",
index: false,
redirect: false,
}),
};Customizing input sources
You can customize the list of request properties that are combined into input that is being validated and available
to your endpoints and middlewares.
import { createConfig } from "express-zod-api";
createConfig({
// ...,
inputSources: {
// the defaults are:
get: ["query", "params"],
post: ["body", "params", "files"],
put: ["body", "params"],
patch: ["body", "params"],
delete: ["query", "params"],
},
});Enabling compression
According to Express.js best practices guide
it might be a good idea to enable GZIP compression of your API responses. You can achieve and customize it by using the
corresponding configuration option when using the createServer() method.
In order to receive the compressed response the client should include the following header in the request:
Accept-Encoding: gzip, deflate. Only responses with compressible content types are subject to compression. There is
also a default threshold of 1KB that can be configured.
import { createConfig } from "express-zod-api";
const config = createConfig({
server: {
// compression: true, or:
compression: {
// @see https://www.npmjs.com/package/compression#options
threshold: "100b",
},
// ... other options
},
// ... other options
});Enabling HTTPS
The modern API standard often assumes the use of a secure data transfer protocol, confirmed by a TLS certificate, also
often called an SSL certificate in habit. When using the createServer() method, you can additionally configure and
run the HTTPS server.
import { createConfig, createServer } from "express-zod-api";
const config = createConfig({
server: {
listen: 80,
},
https: {
options: {
cert: fs.readFileSync("fullchain.pem", "utf-8"),
key: fs.readFileSync("privkey.pem", "utf-8"),
},
listen: 443, // port or socket
},
// ... cors, logger, etc
});
const { app, httpServer, httpsServer, logger } = createServer(config, routing);At least you need to specify the port or socket (usually it is 443), certificate and the key, issued by the certifying authority. For example, you can acquire a free TLS certificate for your API at Let's Encrypt.
Generating a Frontend Client
There is a new way of informing the frontend about the I/O types of your endpoints starting the version 6.1.0. The new approach offers automatic generation of a client based on routing to a typescript file. The generated client is flexibly configurable on the frontend side using an implementation function that directly makes requests to an endpoint using the libraries and methods of your choice. The client asserts the type of request parameters and response. Consuming the generated client requires Typescript version 4.1 or higher.
// example client-generator.ts
import { writeFileSync } from "node:fs";
import { Integration } from "express-zod-api";
writeFileSync(
"./frontend/client.ts",
new Integration({
routing,
variant: "client", // <โ optional, see also "types" for a DIY solution
optionalPropStyle: { withQuestionMark: true, withUndefined: true }, // optional
}).print(),
"utf-8",
);// example frontend, simple implementation based on fetch()
import { ExpressZodAPIClient } from "./client.ts";
const client = new ExpressZodAPIClient(async (method, path, params) => {
const hasBody = !["get", "delete"].includes(method);
const searchParams = hasBody ? "" : `?${new URLSearchParams(params)}`;
const response = await fetch(`https://example.com${path}${searchParams}`, {
method: method.toUpperCase(),
headers: hasBody ? { "Content-Type": "application/json" } : undefined,
body: hasBody ? JSON.stringify(params) : undefined,
});
return response.json();
});
client.provide("get", "/v1/user/retrieve", { id: "10" });
client.provide("post", "/v1/user/:id", { id: "10" }); // it also substitues path paramsCreating a documentation
You can generate the specification of your API and write it to a .yaml file, that can be used as the documentation:
import { Documentation } from "express-zod-api";
const yamlString = new Documentation({
routing, // the same routing and config that you use to start the server
config,
version: "1.2.3",
title: "Example API",
serverUrl: "https://example.com",
composition: "inline", // optional, or "components" for keeping schemas in a separate dedicated section using refs
}).getSpecAsYaml();You can add descriptions and examples to your endpoints, their I/O schemas and their properties. It will be included into the generated documentation of your API. Consider the following example:
import { defaultEndpointsFactory, withMeta } from "express-zod-api";
const exampleEndpoint = defaultEndpointsFactory.build({
shortDescription: "Retrieves the user.", // <โโ this becomes the summary line
description: "The detailed explanaition on what this endpoint does.",
input: withMeta(
z.object({
id: z.number().describe("the ID of the user"),
}),
).example({
id: 123,
}),
// ..., similarly for output and middlewares
});See the example of the generated documentation here
Tagging the endpoints
When generating documentation, you may find it necessary to classify endpoints into groups. For this, the
possibility of tagging endpoints is provided. In order to achieve the consistency of tags across all endpoints, the
possible tags should be declared in the configuration first and another instantiation approach of the
EndpointsFactory is required. Consider the following example:
import {
createConfig,
EndpointsFactory,
defaultResultHandler,
} from "express-zod-api";
const config = createConfig({
// ..., use the simple or the advanced syntax:
tags: {
users: "Everything about the users",
files: {
description: "Everything about the files processing",
url: "https://example.com",
},
},
});
// instead of defaultEndpointsFactory use the following approach:
const taggedEndpointsFactory = new EndpointsFactory({
resultHandler: defaultResultHandler, // or use your custom one
config, // <โโ supply your config here
});
const exampleEndpoint = taggedEndpointsFactory.build({
// ...
tag: "users", // or tags: ["users", "files"]
});How to test endpoints
The way to test endpoints is to mock the request, response, and logger objects, invoke the execute() method, and
assert the expectations for calls of certain mocked methods. The library provides a special method that makes mocking
easier, it requires jest (and optionally @types/jest) to be installed, so the test might look the following way:
import { testEndpoint } from "express-zod-api";
test("should respond successfully", async () => {
const { responseMock, loggerMock } = await testEndpoint({
endpoint: yourEndpoint,
requestProps: {
method: "POST", // default: GET
body: { /* parsed JSON */ },
},
// responseProps, configProps, loggerProps
});
expect(loggerMock.error).toBeCalledTimes(0);
expect(responseMock.status).toBeCalledWith(200);
expect(responseMock.json).toBeCalledWith({
status: "success",
data: { ... },
});
});This method is optimized for the defaultResultHandler. With the flexibility to customize, you can add additional
properties as needed.
Caveats
There are some well-known issues and limitations, or third party bugs that cannot be fixed in the usual way, but you should be aware of them.
Coercive schema of Zod
Despite being supported by the library, z.coerce.* schema
does not work intuitively.
Please be aware that z.coerce.number() and z.number({ coerce: true }) (being typed not well) still will NOT allow
you to assign anything but number. Moreover, coercive schemas are not fail-safe and their methods .isOptional() and
.isNullable() are buggy. If possible, try to avoid using this type
of schema. This issue will NOT be fixed in
Zod version 3.x.
Excessive properties in endpoint output
The schema validator removes excessive properties by default. However, Typescript does not yet display errors in this case during development. You can achieve this verification by assigning the output schema to a constant and reusing it in forced type of the output:
import { z } from "zod";
const output = z.object({
anything: z.number(),
});
endpointsFactory.build({
methods,
input,
output,
handler: async (): Promise<z.input<typeof output>> => ({
anything: 123,
excessive: "something", // error TS2322, ok!
}),
});Your input to my output
Do you have a question or idea? Your feedback is highly appreciated in Discussions section.
Found a bug? Please let me know in Issues section.
Found a vulnerability or other security issue? Please refer to Security policy.