OpenAPI Generator for serverless

This will generate an OpenAPI V3 (up to v3.0.3) file for you from your serverless file. It can optionally generate a Postman Collection V2 from the OpenAPI file for you too.

Originally based off of: https://github.com/temando/serverless-openapi-documentation

Install

This plugin works for Serverless 2.x and up and only supports node.js 14 and up.

To add this plugin to your package.json:

Using npm:

npm install --save-dev serverless-openapi-documenter

Next you need to add the plugin to the plugins section of your serverless.yml file.

plugins:
  - serverless-openapi-documenter

Note: Add this plugin after serverless-offline to prevent issues with String.replaceAll being overridden incorrectly.

Adding documentation to serverless

To Run: serverless openapi generate -o openapi.json -f json -a 3.0.3 -p postman.json

Options:

--output                -o  What filename the OpenAPI documentation should output under. Default: openapi.json
--format                -f  Whether to output the OpenAPI documentation as json or yaml. Default: json
--indent                -i  File indentation in spaces. Default: 2
--openApiVersion        -a  OpenAPI version to generate for. Default: 3.0.0
--postmanCollection     -p  Will generate a postman collection (from the generated openAPI documentation), in json only, if passed in. Default postman.json

OpenAPI Mapping

Configuration

To configure this plugin to generate valid OpenAPI documentation there are two places you'll need to modify in your serverless.yml file, the custom variables section and the http event section for each given function in your service.

The custom section of your serverless.yml can be configured as below:

custom:
  documentation:
    version: '1'
    title: 'My API'
    description: 'This is my API'
    externalDocumentation:
      url: https://google.com
      description: A link to google
    servers:
      url: https://example.com
      description: The server
    tags:
      - name: tag1
        description: this is a tag
        externalDocumentation:
          url: https://npmjs.com
          description: A link to npm
    models: {}

Mostly everything here is optional. A version from a UUID will be generated for you if you don't specify one, title will be the name of your service if you don't specify one.

These configurations can be quite verbose; you can separate it out into it's own file, such as serverless.doc.yml as below:

custom:
  documentation: ${file(serverless.doc.yml):documentation}

functions:
  myFunc:
    events:
      - http:
          path: getStuff
          method: get
          documentation: ${file(serverless.doc.yml):endpoints.myFunc}

For more info on serverless.yml syntax, see their docs.

Models

There are two ways to write the Models. Models contain additional information that you can use to define schemas for endpoints. You must define the content type for each schema that you provide in the models.

The first way of writing the model is: required directives for the models section are as follow:

• name: the name of the schema
• description: a description of the schema
• contentType: the content type of the described request/response (ie. application/json or application/xml).
• schema: The JSON Schema (website) that describes the model. You can either use inline YAML to define these or use either an external file schema that serverless will resolve (as below), or a reference to an externally hosted schema that will be attempted to be resolved.

custom:
  documentation:
    models:
      - name: "ErrorResponse"
        description: "This is an error"
        contentType: "application/json"
        schema: ${file(models/ErrorResponse.json)}
      - name: "PutDocumentResponse"
        description: "PUT Document response model (external reference example)"
        contentType: "application/json"
        schema: ${file(models/PutDocumentResponse.json)}
      - name: "PutDocumentRequest"
        description: "PUT Document request model (inline example)"
        contentType: "application/json"
        schema:
          $schema: "http://json-schema.org/draft-04/schema#"
          properties:
            SomeObject:
              type: "object"
              properties:
                SomeAttribute:
                  type: "string"

The Second way of writing the models:

• name: the name of the schema
• description: a description of the schema
• content: an Object made up of the contentType and the schema, as shown below

custom:
  documentation:
    models:
      - name: "ErrorResponse"
        description: "This is an error"
        content:
          application/json:
            schema: ${file(models/ErrorResponse.json)}
      - name: "PutDocumentResponse"
        description: "PUT Document response model (external reference example)"
        content:
          application/json:
            schema: ${file(models/PutDocumentResponse.json)}
      - name: "PutDocumentRequest"
        description: "PUT Document request model (inline example)"
        content:
          application/json:
            schema:
              $schema: "http://json-schema.org/draft-04/schema#"
              properties:
                SomeObject:
                  type: "object"
                  properties:
                    SomeAttribute:
                      type: "string"

Functions

To define the documentation for a given function event, you need to create a documentation attribute for your http event in your serverless.yml file.

The documentation section of the event configuration can contain the following attributes:

• summary: a short description of the method
• description: a detailed description of the method
• tags: an array of tags for this event
• deprecated: boolean indicator that indicates clients should migrate away from this function
• requestBody: contains description of the request
  • description: a description of the request body
• requestModels: a list of models to describe the request bodies (see requestModels below)
• queryParams: a list of query parameters (see queryParams below)
• pathParams: a list of path parameters (see pathParams below)
• cookieParams: a list of cookie parameters (see cookieParams below)
• methodResponses: an array of response models and applicable status codes
  • statusCode: applicable http status code (ie. 200/404/500 etc.)
  • responseBody: contains description of the response
    • description: a description of the body response
  • responseHeaders: a list of response headers (see responseHeaders below)
  • responseModels: a list of models to describe the request bodies (see responseModels below) for each Content-Type

functions:
  createUser:
    handler: handler.create
    events:
      - http:
        path: create
        method: post
        summary:
        documentation:
          summary: "Create User"
          description: "Creates a user and then sends a generated password email"
          tags:
            - tag1
          externalDocumentation:
            url: https://bing.com
            description: A link to bing
          requestBody:
            description: "A user information object"
          requestModels:
            application/json: "PutDocumentRequest"
          pathParams:
            - name: "username"
              description: "The username for a user to create"
              schema:
                type: "string"
                pattern: "^[-a-z0-9_]+$"
          queryParams:
            - name: "membershipType"
              description: "The user's Membership Type"
              schema:
                type: "string"
                enum:
                  - "premium"
                  - "standard"
          cookieParams:
            - name: "SessionId"
              description: "A Session ID variable"
              schema:
                type: "string"
          methodResponses:
            - statusCode: 201
              responseBody:
                description: "A user object along with generated API Keys"
              responseModels:
                application/json: "PutDocumentResponse"
            - statusCode: 500
              responseBody:
                description: "An error message when creating a new user"
              responseModels:
                application/json: "ErrorResponse"

queryParams

Query parameters can be described as follow:

• name: the name of the query variable
• description: a description of the query variable
• required: whether the query parameter is mandatory (boolean)
• schema: JSON schema (inline, file or externally hosted)

queryParams:
  - name: "filter"
    description: "The filter parameter"
    required: true
    schema:
      type: "string"

pathParams

Path parameters can be described as follow:

• name: the name of the query variable
• description: a description of the query variable
• schema: JSON schema (inline, file or externally hosted)

pathParams:
  - name: "usernameId"
    description: "The usernameId parameter"
    schema:
      type: "string"

cookieParams

Cookie parameters can be described as follow:

• name: the name of the query variable
• description: a description of the query variable
• required: whether the query parameter is mandatory (boolean)
• schema: JSON schema (inline, file or externally hosted)

cookieParams:
  - name: "sessionId"
    description: "The sessionId parameter"
    required: true
    schema:
      type: "string"

requestModels

The requestModels property allows you to define models for the HTTP Request of the function event. You can define a different model for each different Content-Type. You can define a reference to the relevant request model named in the models section of your configuration (see Defining Models section).

requestModels:
  application/json: "CreateRequest"
  application/xml: "CreateRequestXML"

methodResponses

You can define the response schemas by defining properties for your function event.

For an example of a methodResponses configuration for an event see below:

methodResponse:
  - statusCode: 200
    responseHeaders:
      - name: "Content-Type"
        description: "Content Type header"
        schema:
          type: "string"
    responseModels:
      application/json: "CreateResponse"
      application/xml: "CreateResponseXML"

responseModels

The responseModels property allows you to define models for the HTTP Response of the function event. You can define a different model for each different Content-Type. You can define a reference to the relevant response model named in the models section of your configuration (see Defining Models section).

responseModels:
  application/json: "CreateResponse"
  application/xml: "CreateResponseXML"

responseHeaders and requestHeaders

The responseHeaders/requestHeaders section of the configuration allows you to define the HTTP headers for the function event.

The attributes for a header are as follow:

• name: the name of the HTTP Header
• description: a description of the HTTP Header
• schema: JSON schema (inline, file or externally hosted)

responseHeaders:
  - name: "Content-Type"
    description: "Content Type header"
    schema:
      type: "string"
requestHeaders:
  - name: "Content-Type"
    description: "Content Type header"
    schema:
      type: "string"

Example configuration

Please view the example [serverless.yml](test/serverless\ 2/serverless.yml).

Notes on schemas

Schemas can be either: inline, in file or externally hosted. If they're inline or in file, the plugin will attempt to normalise the schema to OpenAPI 3.0.X specification.

If they exist as an external reference, for instance:

schema: https://raw.githubusercontent.com/SchemaStore/schemastore/master/src/schemas/json/bettercodehub.json

We use the plugin JSON Schema $Ref Parser to attempt to parse and resolve the references. There are limitations to this. Consider the schema:

{
    "$schema": "https://json-schema.org/draft-04/schema",
    "title": "Reusable Definitions",
    "type": "object",
    "id": "https://raw.githubusercontent.com/json-editor/json-editor/master/tests/fixtures/definitions.json",
    "definitions": {
        "address": {
            "title": "Address",
            "type": "object",
            "properties": {
                "street_address": { "type": "string" },
                "city":           { "type": "string" },
                "state":          { "type": "string" }
            },
            "required": ["street_address"]
        },
        "link" : {"$refs": "./properties.json#/properties/title"}
    },
    "properties": {
        "address" : {"$refs": "#/definitions/address"}
    }
  }

Where the definition "link" refers to a schema held in a directory that the resolver does not know about, we will not be able to fully resolve the schema which will likely cause errors in validation of the openAPI 3.0.X specification.

Because of the dependency we use to parse externally linked schemas, we can supply our own options to resolve schemas that are more difficult than a straight forward example.

You can create your own options file: https://apitools.dev/json-schema-ref-parser/docs/options.html to pass into the dependency that contains it's own resolver to allow you to resolve references that might be in hard to reach places. In your main project folder, you should have a folder called options with a file called ref-parser.js that looks like:

'use strict'

// options from: https://apitools.dev/json-schema-ref-parser/docs/options.html

module.exports = {
  continueOnError: true,            // Don't throw on the first error
  parse: {
    json: false,                    // Disable the JSON parser
    yaml: {
      allowEmpty: false             // Don't allow empty YAML files
    },
    text: {
      canParse: [".txt", ".html"],  // Parse .txt and .html files as plain text (strings)
      encoding: 'utf16'             // Use UTF-16 encoding
    }
  },
  resolve: {
    file: false,                    // Don't resolve local file references
    http: {
      timeout: 2000,                // 2 second timeout
      withCredentials: true,        // Include auth credentials when resolving HTTP references
    }
  },
  dereference: {
    circular: false,                // Don't allow circular $refs
    excludedPathMatcher: (path) =>  // Skip dereferencing content under any 'example' key
      path.includes("/example/")
  }
}

If you don't supply this file, it will use the default options.

License

MIT