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Building SoftwareWebAPI Design Guide

Date: 24-Apr-2017

Alexander Goida

Presenter

Alexander Goida

Senior Software Engineer – StarChef

Knowledge Sharing facilitator – Sofia

Almost 2 years in Fourth and 14 years in IT as Software Developer

Topics for today

• Web Services overview

• RESTful service principles

• Example: Book Store inventory• Define Domain model

• Define resources

• Adhere IT standards

• Design classes

• Testing

Web Services overviewThere are no rules of architecture for a castle in the clouds.

Web Services overview: Simplified architecture

Web Services overview: WCF protocols

WCF Services

• Supports multiple protocols

• Strong typing

• Very configurable

• Complex for heterogeneous system

• Supports GET, POST by default

Web Services overview: Web API protocols

Web API Services

• Simple

• Supports all HTTP verbs & features

• Supports MVC features

• Supports only HTTP protocol

• No strong typing

Web Services overview: Architectural styles

• Endpoint contains routine name

• Good when exposing existing routines to web

• Good when server keeps the state

• Simpler to design

• Endpoint contains resource name

• Good for new systems

• Good for stateless operations

• Good for Javascript clients

• Closer to web

RESTful service principlesThere are three constants in life... change, choice and principles.

RESTful service principles

1. Uniform Interface

2. Stateless Interactions

3. Cacheable

4. Client-Server

5. Layered System

6. Code on Demand (optional)

RESTful service principles

Level 0: Swamp of POX

• Plain Old XML

• XML-RPC, SOAP

Level 1: Resources

Level 2: HTTP verbs

• All verbs

• HTTP Status Codes

Level 3: Hypermedia controls

• HATEOAS

• Dynamic discovery of endpoints

Richardson Maturity Model

Ideal RESTful

service

Most of REST services

Example: Book Store inventoryThe practice killed hedgehog who knew how to eat cactus safely

Example: Book Store inventory

• Simple business model

• RESTful service (level 2)

• Supports• CRUD operations

• OData queries

• Documented (Swagger)

• Versioned

• Source code at GitHub

Example: Book Store inventory

Domain Model

Bounded contexts

Resources

Service granularity

Standards

HATEOAS

Open API

OData

Versioning

Security

Basic Authentication

OAuth

Classes

SOLID

Software Patterns

Designing steps & Considerations

1 2 3 4 5

Example: Book Store inventory

• Bounded context

• Aggregation root

• Entity

• Value object

Define Domain Model

Example: Book Store inventory

• Use your Domain model

• Define “language” to your API

• Root & Dependent resources• GET /authors

• DELETE /authors/ID

• GET /authors/ID/books

• Anti-patterns• GET /authors/delete?id=GUID

• POST /GetPublisherDetails

• POST /author/create

Define Resources

Example: Book Store inventory

• HATEOAS - Hypermedia as the Engine of Application State

• The essential part of the "uniform interface"

• API is discovered dynamically through interaction with the service

Adhere industry standards{

"class": [ "order" ],"properties": {

"orderNumber": 42, "itemCount": 3,"status": "pending"

},"entities": [

{ "class": [ "items", "collection" ], "rel": [ "http://x.io/rels/order-items" ], "href": "http://api.x.io/orders/42/items"

},{"class": [ "info", "customer" ],"rel": [ "http://x.io/rels/customer" ], "properties": {

"customerId": "pj123","name": "Peter Joseph"

},"links": [

{ "rel": [ "self" ], "href": "http://api.x.io/customers/pj123" }]

}],"actions": [

{"name": "add-item","title": "Add Item","method": "POST","href": "http://api.x.io/orders/42/items","type": "application/x-www-form-urlencoded","fields": [

{ "name": "orderNumber", "type": "hidden", "value": "42" },{ "name": "productCode", "type": "text" },{ "name": "quantity", "type": "number" }

]}

],"links": [

{ "rel": [ "self" ], "href": "http://api.x.io/orders/42" },{ "rel": [ "previous" ], "href": "http://api.x.io/orders/41" },{ "rel": [ "next" ], "href": "http://api.x.io/orders/43" }

]}

{ "orderNumber": 42, "itemCount": 3,"status": "pending"

}

Example: Book Store inventory

• Open API Specification (Swagger 2.0)

• JSON base specification

• Language-agnostic specification of RESTful APIs

• Server proxy can be auto-generated

• Swashbuckle automates for .NET with UI

Adhere industry standards

Example: Book Store inventory

• OData – Open Data Protocol to query data in RESTful APIs

• Deal with a lot of data

• Filtering, sorting and paging

Adhere industry standards

Query Option Sample Description

$filter /authors?$filter=Name eq ‘name’

/authors?$filter=contains(Name, ‘name')

filter a collection of resources that are

addressed by a request

$orderby /authors?$orderby=Name desc request resources in asc or desc order

$select /authors?$select=Name requests a limited set of properties for

each entity

$skip & $top /authors?$skip=5

/authors?$top=5

request a limited number of records

Example: Book Store inventory

• Versioning:• MAJOR for breaking changes• MINOR for backwards-compatible changes• PATCH for backwards-compatible bug fixes

• In general only MAJOR is used

Adhere industry standards

Style Sample

URL /api/v2/authors

Custom header /api/authors

Header: api-version=2

Accept header Accept: application/vnd.bookstore.v2+json

Also Possible:

• /api/foo?api-version=1.0

• /api/foo?api-version=2.0-Alpha

• /api/foo?api-version=2015-05-01.3.0

• /api/v2.0-Alpha/foo

• /api/v2015-05-01.3.0/foo

Example: Book Store inventory

• SOLID• Use constructor for injecting• Low coupling, High cohesion

• KISS, YAGNI, DRY

• Patterns• Data Mapper• Dependency Injection• Repository• Unit Of Work

• Anti-patterns• Service locator• God object

Design classes

Example: Book Store inventory

Design classes

TestingTest less, but tests smarter

Testing

• Vision• Defend your solution with tests• Consider use cases of methods• Test requirements, not everything• The less integration tests, the better

• Unit testing• AAA style• Isolated tests• Better to test through public methods

• Integration testing• In-Memory hosting is simple• Check routing and database

• Manual testing• Tools Swagger UI, Postman

Glossary

• WCF• Windows Communication Foundation, a framework for building service-oriented application software

• REST• Representational State Transfer, the architectural style which allows clients manipulate web resources using stateless operations

• HATEOAS• Hypermedia as the Engine of Application State, a constraint of RESTful style which allows a client to interact with a service

through hypermedia provided dynamically

• SOAP• Simple Object Access Protocol, a protocol specification based on XML for exchanging structured information independent of

language and platforms

• RPC• Remote Procedure Call, an inter-process communication technique in networked computing

• Named Pipes• An inter-process communication technique within same machine

• OData• Open Data Protocol, an open protocol which allows the creation and consumption of queryable APIs

Reading Material & Sources

1. Modern Web App Architecture (web link)

2. Chapter 21: Designing Web Applications (web link)

3. Difference between WCF and Web API and WCF REST and Web Service (web link)

4. Do you really know why you prefer REST over RPC? (web link)

5. What Is REST? (web link)

6. Richardson Maturity Model (web link)

7. API design (web link)

8. Choosing a hypermedia type for your API (web link)

9. Choosing a Transport (web link)

10. Best Practices for Designing a Pragmatic RESTful API (web link)

11. Adding Swagger to Web API project (web link)

12. Demystify Web API Versioning (web link)

13. Introduction to OData (video)

14. OData tutorial (web link)

Final questions?

Too much information?But this is just the beginning!