OpenAPI codegen for TypeScript

What is this?

This is a TypeScript code generator which generates TypeScript types and interfaces base on your OpenAPI document, including

• schemas
• IHandler, types and interfaces for both server and client api
• apiRouter, server api partial implementation using koa router
• ClientAPI, client api implementation using axios

This tool assumes you use koa router for server and axios for client.

How to use this tool?

0. Install it

yarn add -D @sup39/api-ts-gen

Also, install the dependencies that generated code will use.

yarn add koa @koa/router koa-body
yarn add -D @types/koa @types/koa__router axios

1. Write your OpenAPI document

You can use Swagger Editor to edit your api document. Make sure to follow the OpenAPI Specification.

This tool generates code from paths and components/schemas.
⚠️ only get, post, update, delete, patch are supported in paths

2. Set path alias

Determine the output directory for generated code and the server api implementation location, and edit your tsconfig.json:

{
  // ...
  "compilerOptions": {
    // ...
    "baseUrl": ".", // or your project root
    "paths": {
      // ...
      "#api/*": ["path/to/your/output/directory/for/generated/code/*"],
      "#ServerAPI": ["path/to/your/server/api/implementation"]
    }
  }
}

If you use webpack, you should also edit your webpack.config.js:

module.exports = {
  // ...
  resolve: {
    // ...
    alias: {
      '#api': 'path/to/your/output/directory/for/generated/code',
      // #ServerAPI is not required
    },
  },
};

3. Run this tool

yarn run api-codegen <your-openapi-document> [-o <output-dir>] [-s <ctx.state-interface-path>] [-c]

The default output directory is api/generated.
For example, if you put your api document at api.yml, and want the generated code put in generated/ directory, you can execute

# example
yarn run api-codegen api.yml -o generated

Flags(Optional)

• -o --output-dir <output-dir>: output directory(default: api/generated)
• -c --client-only: client code only(default: client & server)

4. Implement server api

import {IServerAPI} from '#api/IServerAPI';

export default {
  operationId: async (req, state, ctx) => {
    // ...
    return [status, body];
  },
  // ...
} as IServerAPI;

The function name is the operationId defined in the api document.
There are 3 arguments passed to the function.

req

The request parameters and body, defined in parameters and requestBody.
Any parameter will be put in req.{in}.{name}, where {in} is one of path, query, header, cookie.
requestBody will be put in req.body.

state

Alias to ctx.state

You can specify the type of ctx.state by setting the export default type to IServerAPI<YourStateType>.

// example
import {IServerAPI} from '#api/IHandler';

interface IState {
  user: {
    id: number;
  }
}
export default {
  // ...
  operationId: async (req, state, ctx) => {
    // state has IState type here
    state.user.id // number
    // ...
  },
} as IServerAPI<IState> // specify ctx.state type to IState

ctx

The ctx object from koa router. Avoid to use it unless required.

// Don't do this
ctx.body = responseBody;
ctx.status = statusCode;
// Do this
return [statusCode, responseBody];

return value

[status, body] If the responseBody is not required, you can omit it or pass anything to it.

// example
return [200, {...}];
return [404, 'some response string'];

// if responseBody is not required
return [statusCode]; // OK
return [statusCode, 'message string']; // OK
return [statusCode, {some: 'object'}]; // OK

5. Mount the api router to server

import * as Koa from 'koa';
import apiRouter from '#api/apiRouter';

const app = new Koa();
// some other entry

app.use(apiRouter.prefix('/your/api/prefix').routes());
// or simply app.use(apiRouter.routes());

app.listen(yourAppListenPort);

6. Use api in client

Simply import and use it! Like the server api, the function name will be the operationId defined in the api document, and the parameters will be the parameters and requestBody if defined.

api.{operationId}([path], [query], [header], [cookie], [body])

where the path, query, header, cookie is a object whose key is the name defined in parameters in the api document, and body is the requestBody.

💡 Note that if the method is patch, req.body will be Partial, which means that any property can be omitted.

import api from '#api/ClientAPI';
// import {FullDate} from '@sup39/api-ts-gen/dist/utils';
// import {SchemaA} from '#api/schemas';

// ...
api.operationWithPath({pathName: pathValue});
api.operationWithQueryAndBody({queryName: queryValue}, body);
api.operationWithPathAndQueryAndBody({
  pathName1: pathvalue1,
  pathName2: pathvalue2,
  pathName3: pathvalue3,
}, {
  queryName1: queryvalue1,
  queryName2: queryvalue2,
}, body);

If you set the prefix of the api, you have to set the $baseURL of client api.

api.$baseURL = '/same/as/the/prefix/in/server';

FullDate

If the format is string date, you should use FullDate instead of Date. FullDate is a wrapper of Date, which implements .toString(), .toJSON() and .valueOf() to make it more convenience to convert it to String or JSON.

Import FullDate class from @sup39/api-ts-gen/dist/utils.

import {FullDate} from '@sup39/api-ts-gen/dist/utils';

// initialization
new FullDate(new Date()); // from a Date instance
new FullDate(); // today
new FullDate('2012-03-31'); // 2012-03-31
new FullDate(2015, 5); // 2015-05-01
new FullDate(2015, 5, 4); // 2015-05-04
new FullDate(1449446400000); // 2015-12-07

// getter
const d = new FullDate();
d.date // a Date instance clone
d.year // date.getUTCFullYear()
d.month // date.getUTCMonth()+1
d.day // date.getUTCDate()
d.dayOfWeek // date.getUTCDay()

// setter
d.year = 2018; // date.setUTCFullYear(2018)
d.month = 3; // date.setUTCMonth(3-1)
d.day = 5; // date.setUTCDate(5)

// method
/* CAUTION: this method has been updated since version 2.0.6
  .advance(period: number): this
  return this advanced by $peroid days
*/
const d0 = new FullDate('2015-05-04');
d0.advance(217) // 2015-12-07
d0.advance(-1129) // 2012-03-31
d0 === d0.advance(-1129) // true

/*
  .advanced(period: number): FullDate
  return a new FullDate advanced by $peroid days
*/
const d0 = new FullDate('2015-05-04');
d0.advance(217) // 2015-12-07
d0.advance(-1129) // 2012-03-31
d0 === d0.advance(-1129) // false

/*
  .distanceFrom(d0: FullDate): number
  return the distance(unit: day) from d0
*/
d0.distanceFrom(new FullDate(2018, 3, 5)); // -1036
d0.distanceFrom(new FullDate(2007, 8, 31)); // 2803

⚠️ FullDate use month from 1 to 12, which differs from Date. Also, FullDate use day and dayOfWeek instead of date and day.

Schema

It is not necessary to use SomeSchema.from(...) of SomeSchema.Partial(...) to create an instance to pass to the client api. Instead, simply use an object literal.

Import the schema type interfaces from #api/schemas.

import {SchemaA, SchemaB} from '#api/schemas';

api.postA({id: 3}, {...}) // OK, simpler
api.postA({id: 3}, SchemaA.from(...)); // Well, still OK
api.patchB({id: 3}, {...}) // OK, simpler
api.patchB({id: 3}, SchemaB.Partial(...)); // Well, still OK

⚠️ From v2.0.0, Schemas are no longer class. Instead, it became a interface and a Object including from, Partial, and fields properties.

Handling response

The api is a async function that returns a APIPromise, which is a extended Promise. The promise is resolved if the status code is 2xx, otherwise it is rejected.

Every operation has a different APIPromise definition according to the possible response status code. If there is only one 2xx in the status code and error handling is not required, you can simply use await to get the response body.

const a: SchemaA = await api.getA(...);

However, if you want to handle several kinds of response, you can use .on(statusCode, responseBody => handler) where XXX is the status code.

api.getA(...)
  .on(200, a => { // the compiler knows that type of `a` is `SchemaA`
    console.log('Get a successfully', a);
  })
  .on(404, msg => {
    console.log('Not found with msg', msg);
  })
  .on(403, () => {
    console.log('Forbidden with no msg');
  });

⚠️ For any status, you can only call .on(status, ...) once.

// OK
api.getA(...)
  .on(200, a => ...)
  .on(403, () => ...)

// NG
api.getA(...)
  .on(200, a => ...)
  .on(200, () => ...) // Compile Error!

Details

Type Conversion

OpenAPI data types will be convert to TypeScript types as following:

type	format		TypeScript
integer		→	number
number		→	number
string		→	string
boolean		→	boolean
string	date	→	FullDate
string	date-time	→	Date
In addition, assigning nullable: true makes it nullable.

Strict Type Parser(STP)

To ensure type safety, STP provides some static functions to convert any type to specific type.

type	format	valid type	note
integer	int32	number, string	integer between -2147483648 and 2147483647 only
integer	int64	number, string	no check for range and floating point
number		number, string	NaN and Infinity is valid
string		string
boolean		boolean, number, string
string	date	FullDate, Date, number, string
string	date-time	Date, number, string
string	byte	string, Buffer	no validation check
string	binary	string, Buffer	no validation check
In addition, assigning nullable: true makes it nullable.

// integer.int32
39 // OK
'39' // OK
'1e3' // NG, no scientific notation
3.14 // NG, not a integer
2147483648 // NG, overflow
'1e100' // NG, overflow
NaN // NG, not a integer
Infinity // NG, not a integer
'pi' // NG, not a number

// integer.int64, number
39 // OK
'39' // OK
'1e3' // OK
3.14 // OK, although it is convertible to int64
2147483648 // OK
'1e100' // OK, although too big for int64
NaN // OK, although it is convertible to int64
Infinity // OK, although it is convertible to int64
'pi' // NG, not a number

// boolean
true, false // OK
'true', 'false' // OK
0, 1, -1, 3.14, Infinity, NaN // OK (Only 0 is converted to false)
'T', 'F' // NG, only 'true' and 'false' are valid
null, {} // NG

// FullDate
new FullDate() // OK
new Date() // OK
'2017-05-28' // OK
1449446400000 // OK, 2015-12-07
'today' // NG, not a valid Date

// Date
new Date() // OK
'2017-05-28' // OK
1449446400000 // OK, 2015-12-07T00:00:00.000Z
new FullDate() // NG
'today' // NG, not a valid Date

// string.byte
'5aeJ5qeY44GL44KP44GE44GE' // OK
'********' // Well, OK, although invalid for a base64 string
Buffer.from('nya') // OK, a Buffer(node.js)
0x52391207 // NG, number is invalid
new Blob([]) // NG, Blob is not supported

// string.
'e5a789e6a798e3818be3828fe38184e38184' // OK
'********' // Well, OK, although invalid for a hex string
Buffer.from('nya') // OK, a Buffer(node.js)
0x52391207 // NG, number is invalid
new Blob([]) // NG, Blob is not supported

Schema

Base on #/components/schemas, it generates interface definitions and constructor functions in schemas.ts.

Interface Definition

For example,

Post:
  type: "object"
  properties:
    id:
      type: "integer"
      format: "int32"
    ts:
      type: "string"
      format: "date-time"
    authorID
      type: "integer"
      format: "int32"
    content:
      type: "string"
      nullable: true
    images:
      type: "array"
      items:
        type: "string"
        format: "binary"
    pinned:
      type: "boolean"

will become

interface Post {
  id: number;
  ts: string;
  authorID: number;
  content: string | null;
  images: string[];
  pinned: boolean;
}

Constructor Function

It also generates constructor function Schema.from with strict type checking. The constructor function takes exactly one argument with literal object type. If any property of the argument is not convertible to expected type, it throws an BadValueError.

For example,

NamedCircle:
  type: "object"
  properties:
    name:
      type: "string"
    radius:
      type: "number"
      format: "double"
    color:
      type: "string"
      nullable: true

will become

interface NamedCircle {
  name: string;
  radius: number;
  color: string | null;
}

Here are some examples for strict type checking:

NamedCircle.from({
  name: 'red circle',
  radius: 39,
  color: 'red',
}); // OK

NamedCircle.from({
  name: 'circle with null color',
  radius: 0,
  color: null,
}); // OK, color is nullable

NamedCircle.from({
  name: 'circle with null color',
  radius: 0,
  color: undefined,
}); // Error! color should be a number or null

NamedCircle.from({
  name: 'circle without given color',
  radius: 0,
}); // Error! color should be given

NamedCircle.from({
  name: 'circle with invalid radius',
  radius: 'miku',
  color: 'cyan',
}); // Error! radius should be a number

Partial Function

It also generates a function called Partial for initializing Partial type. The function also takes exactly one argument. If any property of the argument is absent or is undefined, the function will skip setting the property. However, if the property is given but not convertible to expected type, it throws a BadValueError.

Here are some examples.

NamedCircle.Partial({
  name: 'circle with radius 39',
  radius: 39,
  color: 'cyan',
}); // OK

NamedCircle.Partial({
  name: 'circle without radius and color',
}); // OK

NamedCircle.Partial({
  radius: 1207,
}); // OK

NamedCircle.Partial({}); // OK

NamedCircle.Partial({
  radius: 1207,
  color: null,
}); // OK, color can be null

NamedCircle.Partial({
  name: undefined,
  radius: 1207,
  color: null,
}); // OK, just skip setting name

NamedCircle.Partial({
  name: null,
  radius: 'miku',
  color: 'cyan',
}); // Error! name is not nullable

NamedCircle.Partial({
  radius: 'miku',
  color: 'cyan',
}); // Error! radius should be a number

⚠️ Use object literal if possible. The from and Partial function are mainly for internal use, avoid to use them unless you want to safe and strict convert a any variable to a schema type.

fields

Schema exposes its fields to fields constant. Its type is Array<keyof Schema>.

NamedCircle.fields // ['name', 'radius', 'color']: Array<keyof NamedCircle>

Nested Object

Any object type property which contains id property will be treat specially. When sending request, properties other than id will be removed, for the convenience to work well with Vapor.

For example,

Group:
  type: "object"
  properties:
    id:
      type: "integer"
      format: "int32"
    name:
      type: "string"
    note:
      type: "string"
Person:
  type: "object"
  properties:
    id:
      type: "integer"
      format: "int32"
    group:
      $ref: "#/components/schemas/Group"
    fullName:
      type: "object"
      properties:
        firstName:
          type: "string"
        lastName:
          type: "string"
    age:
      type: "integer"
      format: "int32"

will become

interface Group {
  id: number;
  name: string;
  note: string;
}
interface Person {
  id: number;
  group: Group;
  name: {
    firstName: string;
    lastName: string;
  };
  value: number;
}

However, in http-request function in ClientAPI, the type of the parameter will become

interface Group {
  id: number;
  name: string;
  note: string;
} // no change
interface Task {
  id: number;
  group: {
    id: number;
  }; // properties other than `id` is removed
  name: {
    firstName: string;
    lastName: string;
  }; // no change because there is no `id` property
  value: number;
}

Limitations

application/json only

This tool only supports application/json type for request and response body. Any other type like multipart/form or image/* are not supported and will be ignored.

Versions

2.1.4

• Change import * as XXX to import XXX in codegen of @koa/router and koa-body

2.1.3

• Use JSON.stringify() for pure object in STP._string

2.1.2

• Fix axios query of array type in IClientAPI (add {arrayFormat: 'repeat'})

2.1.1

• Fix axios type bug (AxiosPromise vs Promise<AxiosResponse>)

2.1.0

• Move @sup39/api-ts-gen/utils to @sup39/api-ts-gen/dist/utils since symlink is no longer allowed
• Simplify apiRouter.ts by using router.use to check for BadValueError

2.0.6

• Change Full#advance and implement Full#advanced
• Nest [object-type properties with id property] conversion in request function

2.0.5

• Implement $ref support for responses, parameters, requestBody

2.0.4

• Fix FullDate stringify in Axios params
• Use local timezone instead of UTC in FullDate

2.0.3

• Implement required property of schema
• client-only codegen

2.0.2

• Make number convertible to boolean

2.0.1

• Use IState as a generic type and remove it from api-codegen.

2.0.0

• Simplify generated code
  • Merge all APIPromise class
  • Remove IServerAPI and IClientAPI
• Remove res Object, return [status, body] in ServerAPI instead
• Remove schema classes, use interface instead
• -s flag for ctx.state interface path

1.1.3

• Expose fields of schemas to XXX.fields(static variable)

1.1.2

• Publish to npmjs and change the package name in generated code
• Specify constructor argument type of FullDate

1.1.1

• Implement FullDate#distanceFrom(d0)
• Fix FullDate timezone bug, use UTC instead

1.1.0

• Fix Partial constructor, enhance error msg
• Add int32 STP

1.0.1

• implement FullDate getter, setter, function(advance)

1.0.0

• ClientAPI, ServerAPI interface, Schema TS codegen implemented
• application/json only
• get, post, put, delete, patch only