API Crash Course CWU Startup Club

OUTLINE What is an API? Why are API’s useful? What is HTTP? JSON? XML? What is a RESTful API? How do we consume an API? How do we create an API? API’s are available from many large websites and businesses

WHAT IS AN API? API = Application Programming Interface You use API’s all the time. Scanner class Java Web API: A set of methods exposed over the web via HTTP to allow programmatic access to applications. Allows you to quickly add functionality/data that others have created. Very similar to how a web page works

WHY API’S ARE USEFUL Abstraction / DRY Principle Less data transfer Can be implemented or consumed in almost any language Can expose some methods to public developers Allows frontend developers and backend developers to agree on a common interface

HTTP, JSON, XML Three important technologies that are often used by API’s HTTP: Hyper text transfer protocol, transfers data over a network GET : Read POST : Create PUT : Update PATCH : Partial Update DELETE : Delete JSON: JavaScript Object Notation, a format for data transfer {“key”: “value”, “key2”:{“subkey”: 2, “error”: false}} XML: EXtensible Markup Language: a format for data transfer Designed to be human and machine readable

WHAT IS A RESTFUL API? Uniform Interface Resources (Nouns) URI’s that HTTP Verbs act on. The uniform interface allows Client / Server to evolve independently. Stateless Ever have back button issues? Stateless does not care what order requests are made in. Cacheable Client-Server Separation, client should not manage database, server should not manage UI. Layered System Can uses layered system, cache, middle ware, load balancing, redundancy etc. GitHub's API lets you star a gist with PUT /gists/:id/star and unstar with DELETE /gists/:id/star.

HOW TO CONSUME AN API Firefox: RESTClient Chrome: Postman Online: Examples: POST (Feedback, message) or GET

HOW DO DESIGN AN API Gather requirements from stakeholders Create use cases, and decide the functionality needed Think skeptically, make sure you explore your options Think ahead, make a flexible system Easy To learn and use, even without documentation Hard to misuse Easy to read and maintain code that uses it Sufficiently powerful to satisfy requirements and Appropriate to audience Easy to evolve (Use arrays for example) Rules for a good API

CREATING A SIMPLE API You can use any hostable language with a HTTP library (Almost all of them) Decide your resources, then decide the verbs. Useful to wireframe the UI at this stage Connect to persistent data store Remember the principles of REST Example in Node.JS:

ADVANCED TOPICS Use API Keys pass as a parameter Rate Limiting Headers X-Rate-Limit-Limit - The number of allowed requests in the current period X-Rate-Limit-Remaining - The number of remaining requests in the current period X-Rate-Limit-Reset - The number of seconds left in the current period Authentication A REST API should be stateless, send auth with every request Use ssl, send auth username and base64 password over authentication header Caching HTTP Provides this! Last-Modified header Etag header, hash or checksum, If-None-Match: “etag” Errors { "code" : 1234, "message" : "Something bad happened :(", "description" : "More details about the error here" } Send HTTP Status 400 level 401 unauthorized 403 forbidden 404 not found 405 method not allowed 410 gone (depreciated) 422 Unprocessable entity (validation) 429 Too many requests (Rate limit)