Introduction to RESTful API Modeling Language (RAML)

Introduction to RESTful API Modeling Language (RAML)

1. Overview

RAML is a YAML based language which is built on YAML1.2 and JSON for describing RESTful APIs. It provides all the information necessary to describe Restful API.

It focuses on cleanly describing resources, methods, parameters, responses, media types, and other HTTP constructs that form the basis for modern APIs that obey many, though perhaps not all, Restful constraints.

2. Requirement

Before jumping to RAML. Let’s assume we have to create one web application which is exposing CRUD Operations and couple of query parameters to access USER resources:

· POST /api/v1/users

· GET /api/v1/users

· GET /api/v1/users?username={username}

· GET /api/v1/users/{userId}

· PUT /api/v1/users/userId{}

· DELETE /api/v1/users/{userId}

All the API’s are secured via Basic Authentication and all the communication will be done over HTTPS and all the request response will be in JSON format.

3. Implementation

3.1 Adding Root level details

To start with RAML, first create a file with extension .raml and at rool level, you need to define the setting starting with RAML version.

1. #%RAML 1.0

2. title: REST Services API using Data Types

3. version: v1

4. protocols: [ HTTPS ]

5. baseUri: http://hostname/api/{version}

6. mediaType: application/json

#1 defines the RAML version

#2 Title of the application

#3 API versions

#4 HTTP or HTTPS channel

#5 URL of the application where ‘versions’ refers to a property which will be replaced with #3 version.

#6 Media type for the request/response.

3.2 Add Security

Security should also be added at the root level and as I mentioned earlier all the API’s are secured via Basic Authentication.

1. securitySchemes:
2. basicAuth:
3. description: Basic Authnetication to authenticate API
4. type: Basic Authentication
5. describedBy:
6. headers:
7. Authorization:
8. description: Used to send the Base64-encoded "username:password" credentials
9. type: string
10. example: Authorization NTA5NjUsInN1YiI6IkJhcmNsYXlzX1BheW1lbnRfU2Vydmlj
11. responses:
12. 401:
13. description: |
14. Unauthorized. Username/password is invalid

3.3 Add Data type

Once you are done with security then starts adding all your data type. In my case I will define it for users.

There are multiples ways to define your type:

1. You can create a new file users .raml and include the path over here (Will discuss at the end of this document).

2. Define the types after root setting using expanded syntax

3. Or you can do it via shortcut.

1. types:
2. Users:
3. type: object
4. properties:
5. id:
6. required: true
7. type: integer
8. username:
9. required: true
10. type: string
11. roles:
12. required: false
13. type: string

Now we will see how we can define the user using shorthand.

1. types:

2. Users:

3. properties:

4. id: integer

5. username: string

6. roles?: string

? -> Adding to any property declares that the field is not mandatory.

3.4 Define Resource, method, URL parameters and query parameters

To define a resources

/users:

To add the method

/users:

get:

post:

To add the URL parameters

/users:

get:

post:

/{userId}:

get:

put:

delete:

To add the Query Parameters:

/users:

get:

description: List all users with/without filters

queryParameters:

name?: string

roles?: string

post:

/{userId}:

get:

put:

delete:

Over here, we have seen how we can declare the resources with VERB and how we can define path as well as query parameters.

3.5 Request and Response Body

In above example we have defined the users resources with POST method but have not defined the payload. Let’s see how we can add payload, response and Status Code to an API.

/users:

get:

description: List all users with/without filters

queryParameters:

name?: string

roles?: string

post:

description: create a new user

body:

application/json:

type: Users

example: { "id" : 101, "name" : "Abdul Waheed”, “roles”:”Admin” }

responses:

201:

body:

application/json:

type: Users

example: { "id" : 101, "name" : "Abdul Waheed”, “roles”:”Admin” }

500:

   body:

     application/json:

        type: Error

       example: { "message" : "Internal Server Error, "code" : 500 }

/{userId}:

get:

put:

delete:

In this example, We are performing POST operation where we are passing Users object in the form of JSON and in response we are getting STATUS code as 201 and again response type in the form of JSON.

4. Usage of Includes in RAML

In the above example, we just took one resouces but let’s assume you have to create RAML for your application where you have many resouces and each resouces have multiple consuming API.

Handling such requirement makes our .raml file more verbose and repetetive.

Using !include, we can externalize our duplicate lengthy code.

Eg: we can put the data type for a Users object in the file types/Users.raml and the type for an Error object in types/Error.raml. Then our types section would look like this:

types:

Users: !include types/Users.raml

 Error: !include types/Error.raml

5. Completing the API

After externalizing all of the data types and examples to their files, we can refactor our API using the include facility

1. #%RAML 1.0
2. title: REST Services API using Data Types
3. version: v1
4. protocols: [ HTTPS ]
5. baseUri: http://hostname/api/{version}
6. mediaType: application/json
7. securitySchemes:
8. basicAuth:
9. description: Basic Authnetication to authenticate API
10. type: Basic Authentication
11. describedBy:
12. headers:
13. Authorization:
14. description: Used to send the Base64-encoded "username:password" credentials
15. type: string
16. example: Authorization NTA5NjUsInN1YiI6IkJhcmNsYXlzX1BheW1lbnRfU2Vydmlj
17. responses:
18. 401:
19. description: |
20. Unauthorized. Username/password is invalid
21. types:
22. Users:
23. type: object
24. properties:
25. id:
26. required: true
27. type: integer
28. username:
29. required: true
30. type: string
31. roles:
32. required: false
    type: string
33. /users:
34. get:
35. description: List all users with/without filters
36. queryParameters:
37. name?: string
38. roles?: string
39. response:
40. 200:
41. body:
42. application:json
43. type: Users[]
44. example: [
45. {“id”:1,”username”:”Abdul”}
46. {“id”:2, “username”:”Waheed”}]
47. post:
48. description: create a new user
49. body:
50. application/json:
51. type: Users
52. example: { "id" : 101, "name" : "Abdul Waheed”, “roles”:”Admin” }
53. responses:
54. 201:
55. body:
56. application/json:
57. type: Users
58. example: { "id" : 101, "name" : "Abdul Waheed”, “roles”:”Admin” }
59. 500:
60.    body:
61.      application/json:
62.         type: Error
63.        example: { "message" : "Internal Server Error, "code" : 500 }
65. /{userId}:
66. get:
67. put:
68. delete:

In my next blog, I ll talk about different RAML tools and the difference between SWAGGER (recently renamed to OAS) Vs RAML and which one to prefer.