Super simple introduction to REST-API’sFor programmers

By Patrick Savalle, innovation architect Delta Lloyd NV.

CONTENTS1. HTTP-BASICS

2. REST-BASICS

3. API-BASICS

PART 1HTTP BASICS

REST is HTTP/1.1. It is the native protocol of the web. Advantages are:

• Every tool that can handle Web / HTTP, can handle REST as native ‘content’. For instance gateways, web-servers and browsers can effectively cache, route, verify, manipulate REST requests or responses.

• In short the whole web supports REST

• It is simple and elegant

• Less diversity in technology, you already use HTTP

Part1:~ Http$ WHY REST?_

REST is HTTP. It is the same protocol. Created by the same designer.

Part1:~ Http$ PROTOCOL_

HTTP is a plain text conversation between a client and a server. The conversation is

based on actions performed on resourceswhich are addressed by URL’s.

Part1:~ Http$ URL_

Every resource has an unique URL that consists of several parts.

Part1:~ Http$ VERBS_

The actions that can be performed on a resource are called ‘methods’ or ‘verbs’. Below the most

used verbs (there are many more).

POST – create

PUT – update

DELETE – delete

GET – read

PATCH – partial update

TRACE – echo

HEAD – headers only

Part1:~ Http$ Request_

Requests and responses contain header-fields and possibly ‘content’. Everything is plain text. Headers usually contain metadata or indicate

conversation preferences.

AUTHENTICATION

Part1:~ Http$ JSON RESPONSE_

Part1:~ Http$ STATUS CODES_

Every response contains a status code.

PART 2REST BASICS

Part2:~ Rest$ ENDPOINTS_

The REST protocol is based on ‘endpoints’, which are operations on resources addressed by URL’s.

Endpoints can be bundled to form an API.

ACTION RESOURCE

<verb> https://<host>/<api_version>[/<resource_type>/<instance_id>]

GET https://animal.api/1/lions (returns collection)

GET https://animal.api/1/lions/harry@lion.com (returns single lion)

POST https://animal.api/1/lions (create new element)

PUT https://animal.api/1/lions/harry@lion.com (updates element)

PATCH https://animal.api/1/lions/harry@lion.com (partial update)

DELETE https://animal.api/1/lions (deletes collection)

DELETE https://animal.api/1/lions/harry@lion.com (deletes single element)

GET http://www.example.com/1/customers/33245/orders/8769/lineitems/1

GET https://animal.api/1/lions?start=100&count=50

GET https://animal.api/1/lions?id=100&id=103&id=107 (parameter-array)

Part2:~ Rest$ ACTION + RESOURCE_

An endpoint has a very strict URL structure. This is key to ‘REST’. Map your functional application resources onto the

WWW and allow them to be manipulated.

Part2:~ Rest$ ANTI-PATTERNS_

REST is not SOAP.

An URL is NOT a RPC-address or method,

it is an universal RESOURCE locator

Bad REST API (bad URL’s in general):

POST https://domain.com/updateProfile

POST https://domain.com/deleteProfile

POST https://domain.com/createProfile

Good REST API:

PUT https://domain.com/1/profiles/piet@puk.com

DELETE https://domain.com/1/profiles/piet@puk.com

POST https://domain.com/1/profiles

GET https://domain.com/1/profiles/piet@puk.com

AUTHENTICATION• HTTP BASIC AUTH

Client sends user/password in special header with each API-call. Simple, safe, good choice for API-2-API

• TOKEN AUTH

Get a temporary access token from API, use in API-calls in username part of HTTP BACIS AUTH, simple, safe, good choice for WEB-2-API

• OAUTH2

Industry standard. Flexible. Safe.

Part2:~ Rest$ AUTHENTICATION_

Part2:~ Rest$ JAVA EXAMPLE_

HttpResponse<JsonNode> jsonResponse =

Unirest

.post("http://httpbin.org/post")

.header("accept", "application/json")

.queryString("apiKey", "123")

.field("parameter", "value")

.field("foo", "bar")

.asJson();

PART 3API BASICS

Part3:~ Api$ RULE NUMBER ONE_

A REST-server must be client-state agnostic!

To be flexible and scalable the server needs to be ignorant of client-state or context. A REST-server does not store session data on behalf of the client.

Put another way: all necessary context MUST be in the request. As far as the REST-server is concerned every call is the first call.

Part3:~ Api$ Economy_

There is an API for that. REST-API’s are the glue of the Internet of Things.

Possible clients of your API:

• Other API’s

• Web applications and web front ends (like AngularJS, ReactJS, JQuery web apps)

• Mobile app’s, applications etc.

• Machines, bots

• Typically NOT humans or ‘end users’

API’s are the glue of the internet of things (IoT).

Part3:~ Api$ Users_

On the internet nobody knows you’re a machine.

• Coherent

• Cohesive (Only lists purposeful endpoints)

• Complete (has all necessary endpoints for its purpose)

• Minimal (Only one way to do things)

• Encapsulating (hiding implementation details)

• Self-explaining

• Documented!

Design an API ‘outside-in’, as a product for a generic client. Not just as the library for your specific front-end.

Consider adding the role ‘interface designer’ to the team.

Part3:~ Api$ Interface quality_

Good interface design is crafmanship.

• The API

• Endpoint documentation

• A dashboard to register apps / obtain an API-key

• Language stubs (Java, PHP, Python, etc.) on Github

• Registration on programmableweb and similar

• A homepage / productpage

• A revenue-model / pricing

• A launchparty

• Hackathons

Part3:~ Api$ deliverables_

An API is a product, treat it as such.

Some of the choices only you can make:

• Few methods / large responses vs. many methods / small responses

Considerations: web clients generally like large aggregated responses tailored to their page structures. Other clients like smaller responses. Etc. There is also the underlying (logical) data model and the ‘natural granularity’ of the problem-domain. In most cases: map the data model onto URL’s.

• URL parameters vs request headers (for instance the API-tokens)

Considerations: in general non-functional data should be in headers. Headers are more easily inspected / used by tools like webservers, giving transport flexibility.

• Hypermedia communication (follow-up URL’s in responses, HATEOAS)

Problematic concept, very client dependent. Most API’s don’t have this, why should yours?

Part3:~ Api$ Interface choices_

Good interface design is crafmanship.

• A REST client, e.g. the Chrome POSTMAN plugin (most IDE’s have one as an add-on)

• TELNET (the generic HTTP client)

• http://www.restapitutorial.com/resources.html

• https://github.com/Microsoft/api-guidelines/blob/master/Guidelines.md

• http://jsonapi.org/

Part3:~ Api$ RESOURCES_