APIs

Application Programming Interface

interface that defines interactions between multiple software applications

API

UI

Interfaces for Humans

Interfaces for Software

An API defines...

• Contract: Procedures & Conventions
• Data formats
• Inputs: Calls / Requests
• Outputs: Results / Responses

APIs

• Mostly inflexible
• Ruled by Standards (Ex. IETF)
• Agnostic to programming lang(s)
• Mostly at lower network stack levels
• Wider applicability

• Highly flexible
• Custom Implementation
• Tied to programming language(s)
• At application level
• Specific applicability
• Relies on Protocols to work

Protocols

vs.

https://wiki.c2.com/?ApiVsProtocol

"You use an API, but speak a Protocol"

TCP/IP

UDP

Gopher

FTP

SSH/SFTP

Telnet

SMTP/POP3

HTTP(S)(2)

Protocols (10-100s)

Internet

Streaming

Hypertext

File Transfers

Remote Shells

Email

World Wide Web

APIs (♾)

Libraries / Frameworks

libc, Tensorflow, OpenGL, Rails, protobufs

Operating Systems

POSIX, Win32, DCOM, CORBA, ...

Remote APIs

JDBC, RPC

Web APIs

HTTP, XML-RPC, SOAP, REST, gRPC, GraphQL

Service-specific APIs

Twitter, Stripe, Twilio, Thrillshare, ...

Web APIs

(mostly over HTTP*)

Client-Server model

HTTP

Text-based

<SGML>

- XML

- HTML

Multi-Media

JSON⭐️

Hypertext Transfer Protocol

hypermedia, hyperlinks

WWW (World Wide Web)

by Tim Berners-Lee at CERN in 1989

request–response in the client–server model

Resources located via URLs

Request Methods (aka Verbs):

• HEAD
• GET
• POST
• PUT/PATCH
• DELETE

HTTP

HTTP

So, REST?

Architectural style & set of conventions heavily based on the HTTP protocol to make easier to develop Web APIs :

REST

(Representational State Transfer)

• Client-server: Separation of concerns
• Stateless: Each request is isolated from each other
• Cacheable: Avoid double work and save bandwidth
• Uniform interface: Components based on Resources

Roy Fielding dissertation: http://www.ics.uci.edu/~fielding/pubs/dissertation/top.htm​

Resources

• Key abstraction/entity of information
• Resource identifiers: Usually some sort of ID
• Semantic: Self-descriptive
• Support HTTP CRUD vebs/mehtods:
  • GET
  • PUT/PATCH
  • POST
  • DELETE

Example REST

Usage Lifecycle

Example

Example

Example

Example

Example

Example

Example

Example

Example

Example

Quick Demo

• Browser
• Postman / Insomnia
• cURL (command line)
• Code

Thanks!