Advanced API Design

In this chapter we will move beyond the basics of API design and cover some of the more advanced and powerful features.

How to make your API more 'RESTafarian'

Design principles

Extended HTTP methods
Error handling
Searching, sorting and pagination
Checking for content changes
Multiple Data Formats
Authentication
Logging
HATEOAS
Documenting an API

1 Extended HTTP Methods

HTTP Methods are the verbs that act on collections and elements. CRUD operations require 4 methods.

GET		POST 		PUT		DELETE

Additional Methods

OPTIONS
HEAD
PATCH

2 Error Handling

API consumers see the API as a black box Each response needs to include a status code

401 UNAUTHORISED

Include a human-readable message in the body

{
    message: "Basic Authentication required"
}

3 Searching, Sorting, Partial Responses and Pagination


### Searching a Collection

Search should be considered for collections

Search query passed as a parameter

/books?q=javascript


### Partial Responses

Allows you to supply only the information needed

Reduces the bandwidth

/books?fields=title,author /books/1449336361?fields=title,author

Collection Pagination

Avoid returning the entire collection!

Default limit should be decided (first 20 records?)

Allow developers to specify fewer records

Also need to specify which block to return.

/books?limit=15&offset=45

4 Checking for Content Changes

If the content has not changed since the last time the resource was requested there should be an option to flag this and to offer the option to not download it again. There are two ways to achieve this.

Last-Modified

GET response should include Last-Modified header

GET request should include If-Modified-Since header

If match the server responds with 304 NOT MODIFIED and the headers (no response body)

If content has changed the server responds with 200 OK and requested resource.

ETag

GET response should include ETag header, this is a hashed string.

GET request should include If-None-Match header

If match the server responds with 304 NOT MODIFIED and the headers (no response body)

If content has changed the server responds with 200 OK and requested resource.

Formats

Last-Modified / If-Modified-Since

Uses the RFC 2822 data format

Wed, 21 Oct 2015 07:28:00 GMT

ETag / If-None-Match

Hash of the response body

686897696a7c876b7e

Generating an ETag

Use the etag module

const etag = require('etag')
res.setHeader('ETag', etag(body))

RFC2822 Date Format

Const date = new Date('Tue, 27 Dec 2011 02:12:35 GMT')
Const dateStr = date.toISOString()

5 Multiple Data Formats

Representations

We have already split our application into resources

Resources are your idea of how to divide up the data and present it

The resource is the useful information being presented

The same resource may have several representations

For example a book resource:

A representation containing metadata
A representation containing the book contents

Works in both directions...

Deciding between representations

Two ways to define this:

Unique URI for each representation

Content negotiation

Information sent in the request header

If multiple formats are available client needs to specify

Two options:

Accept header

Accept: application/json

Type format in the URL

/books/1449336361.json

6 Authentication

No authentication status stored in API

Each request must provide the authentication needed

Basic Access Authentication
OAuth 2.0

Basic Access Authentication

Client includes an Authorization header

Username and password combined with a colon

testuser:p455w0rd

This string is encoded using the RFC2045-MIME variant of base64

Printf testuser:p455w0rd | base64
  dGVzdHVzZXI6cDQ1NXcwcmQ=

The result is sent in the header prepended with Basic

Authorization: Basic dGVzdHVzZXI6cDQ1NXcwcmQ=

7 Logging

Need to keep logs of all API requests:

Why is this important?
What useful data can be found in the request?

8 HATEOAS

Lack of standard responses.

Most APIs have their own format, typically a JSON response that maps neatly to their own data model.
Results in lots of APIs that do stuff their own way == confusion

Lack of Hyperlinks

JSON has no built-in support for hyperlinks, which are a fundamental building block on the Web (W3C).
API endpoints are linked together only through documentation.
Forces developers to keep detailed, updated documentation
Forces developers to read and understand it before using the API.

Hypertext As The Engine Of Application State

Richardson Maturity Model

Breaks down the principle elements of REST into three steps

Each step progresses towards the ideal implementation of REST

Developed by Leonard Richardson

Level 0

HTTP as a transport system without web mechanisms

Level 1 – Exposes Resources

Level 2 – Uses Verbs to Manipulate Resources

Can perform different actions on the same resource

Level 3 – Provide links to other resources

Can figure out how to interact with the system

Implementations of HATEOAS

Hypermedia Application Language (HAL)
JSON for Linked Documents (JSON-LD)

Hypermedia Application Language

Open specification describing a generic structure for web resources

Achieves Richardson Maturity Model level 3

Presents a new hypermedia type:

application/hal+json

Individual Resources

{
    "_links": {
        "self": {
            "href": "http://ex.com/books/1449336361"
        }
    },
    "id": "1449336361",
    "name": "JS.Next: ECMAScript 6"
}

Collections

{
    "_links": {
        "self": {
            "href": "http://ex.com/books/1449336361"
        }
    },
    "id": "1449336361",
    "name": "JS.Next: ECMAScript 6"
}

Links

"_links": {
        "self": {
            "href": "http://ex.com/books?page=3"
        },
        "first": {
            "href": "http://ex.com/books"
        },
        "prev": {
            "href": "http://ex.com/books?page=2"
        },
        "next": {
            "href": "http://ex.com/books?page=4"
        },
        "last": {
            "href": "http://ex.com/books?page=133"
        }
    }

Adding a Resource

POST /books HTTP/1.1
Accept: application/json
Content-Type: application/json

{
    "id": "1449336361",
    "name": "JS.Next: ECMAScript 6"
}

HTTP/1.1 201 Created
Content-Type: application/hal+json
Location: http://example.org/api/user/matthew

{
    "_links": {
        "self": {
            "href": "http://ex.com/books/1449336361"
        }
    },
    "id": "1449336361",
    "name": "JS.Next: ECMAScript 6"
}

9 Documenting the API

Important to produce clear documentation

Helps your users understand how it works

Use APIDoc

http://apidocjs.com

Add inline annotations to source code

npm module apidoc generates the documentation

Example:

$ node_modules/.bin/apidoc -e node_modules/ -o docs/api/

This generates the API documentation and creates the web page in the docs/api/ directory. files in the docs/ directory can be published as a website by GitHub. To enable this you should generate the documentation as shown, commit and push the files to GitHub then edit the repository settings and enable GitHub Pages as shown.

This will display a link to the root of the GitHub pages.

Click on this and you get a page not found error. Append api/ to this url and refresh the page to see the documentation.

URLs

There should only be 2 per resource:

Collection (plural)

/books

Resource

/books/1449336361

Summary: Keep verbs out of URLS...

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