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HTTP Request Practice

Week 5 Keywords and Questions

  • What is an HTTP request?
  • What is an HTTP Response?
  • What is the HTTP standard?
  • What types of HTTP requests are there?
  • What is the difference between a Get and a Post?
  • What is HTTP Header?
  • How do I make an HTTP request in vanilla JS?
  • What do the HTTP response codes tell me 1xx, 2xx, 3xx, 4xx, 5xx?

Additional Questions to Consider

  • Why would you pick one way to make a request over another?
  • What affordances to higher-level libraries give us? What does "higher-level library" mean?
  • Aside from ease of use from an engineer perspective, what other pros/cons would a software team use to choose an HTTP library for their project?

Prerequisites

Motivation

HTTP is the most common way you will retrieve anything from the internet: usually web pages or API data (see API & JSON lesson). It's the backbone of the web. Since HTTP is so simple and versatile (it's just text!), you can make requests lots of different ways.

Objectives

Participants will be able to:

  • Make HTTP requests using a variety of mechanisms.

Specific Things to Learn

  • Basics of an HTTP Request
  • Six different ways to make an HTTP request - Postman (Mac GUI app) - curl - XMLHttpRequest (aka AJAX) in the browser - fetch (promises) in the browser - http.request in Node.js - fetch in Node.js

Lesson

HTTP requests are text-based messages used to request a resource from a server. In these lessons we'll focus on GET requests but there are other methods as well, such as POST, which is used on a form to submit data or in an API to save data.

Postman - Time API

Open Postman to make a new GET request.

http://worldtimeapi.org/api/ip

Inspect the result. If you want you can try out other types of requests listed on the API doc. Varying the URL will give you different data.

curl - Time API

Now let's make the same request using the curl command line unix utility.

Find the Code link in Postman on the right.

This will allow us to make the same request using a variety of other tools. Choose cURL from the dropdown.

You will see something like this:

curl -X GET \
  http://worldtimeapi.org/api/ip \
  -H 'Accept: */*' \
  -H 'Accept-Encoding: gzip, deflate' \
  -H 'Cache-Control: no-cache' \
  -H 'Connection: keep-alive' \
  -H 'Host: worldtimeapi.org' \
  -H 'Postman-Token: 8d3f63db-f54f-48fe-997f-f1f678464644,f75b0ac1-ec5e-489d-af1a-fdefc80d56f9' \
  -H 'User-Agent: PostmanRuntime/7.19.0' \
  -H 'cache-control: no-cache'

Copy this entire snippet and paste into Terminal.

You should see output like this:

{"week_number":47,"utc_offset":"-08:00","utc_datetime":"2019-11-20T17:08:24.181139+00:00","unixtime":1574269704,"timezone":"America/Los_Angeles","raw_offset":-28800,"dst_until":null,"dst_offset":0,"dst_from":null,"dst":false,"day_of_year":324,"day_of_week":3,"datetime":"2019-11-20T09:08:24.181139-08:00","client_ip":"69.181.221.255","abbreviation":"PST"}%
Note about HTTP Headers

You might wonder where all those -H lines are coming from when we only put the URL in Postman. As we learned in the HTTP video, headers tell the server additional options. They are like flags in a command line tool or parameters in a JavaScript function. In the case of HTTP, they are almost always optional.

  • Copy only the first two lines and paste it into terminal (do not include the second \)
  • The result should be the same

Why was it the same? In our case, Postman generated a set of sensible defaults. If we omit them, the server will have its own sensible defaults and so the result is more or less the same.

Discussion - Postman & curl
  • If Postman can generate code for curl and other tools, what does that tell us about Postman?

XMLHttpRequest - Time API

Now let's go into the browser world, which is more useful for creating web apps.

First, we will use the original interface, XMLHttpRequest which was added to JavaScript to allow the original background requests commonly called AJAX. It is a little awkward to use.

function reqListener() {
  console.log(this.responseText);
}

let oReq = new XMLHttpRequest();
oReq.addEventListener('load', reqListener);
oReq.open('GET', 'http://worldtimeapi.org/api/ip');
oReq.send();

If correct, you should see the result:

Object { week_number: 47, utc_offset: "-08:00", utc_datetime: "2019-11-20T19:17:12.777523+00:00", unixtime: 1574277432, timezone: "America/Los_Angeles", raw_offset: -28800, dst_until: null, dst_offset: 0, dst_from: null, dst: false, … }

window.fetch - Time API

Newer browsers expose an interface called fetch that is much easier to use and leverages native Promise for simpler processing of the result. And since it is built-in you don't need to add any libraries to use it in the browser.

Let's try it out!

  • Open https://worldtimeapi.org/ in your browser
  • Open the Developer console
  • response = await fetch('https://worldtimeapi.org/api/ip')
  • Once the promise resolves, response will contain a JavaScript object representing the response from the server
  • To see the body as like above, execute await response.json()
fetch - Discussion Questions
  • Notice that even retrieving the body uses Promises (not the await). What are some reasons this might be the way it was designed?
  • Usually you need to be inside an async function to use await? Why didn't we need to worry about that here?
fetch - Browser Compatibility

https://caniuse.com/#feat=fetch

Almost all modern browsers support fetch. Unless your app needs to support IE11, then it's safe to use. Even then, you can polyfill it, e.g. GitHub's polyfill.

Common Mistakes / Misconceptions

Open a new tab to try to issue the same fetch command.

  • Open a new tab to blank or google.com in your browser
  • Open the Developer console
  • response = await fetch('https://worldtimeapi.org/api/ip')
  • Once the promise resolves, response will contain a JavaScript object representing the response from the server
  • To see the body as like above, execute await response.json()

What happens?

To keep things simple, for this example, we just load the same origin, worldtimeapi.org, so we didn't have to worry about it.

http.request in Node

There are too many HTTP libraries to count in Node, but there is one that is built-in that we'll use.

const options = {
  hostname: 'worldtimeapi.org',
  port: 443,
  path: '/api/ip',
  method: 'GET'
};

const req = https.request(options, (res) => {
  console.log(`statusCode: ${res.statusCode}`);

  res.on('data', (d) => {
    process.stdout.write(d);
  });
});

req.end();

Guided Practice

fetch is a standard added by browsers but if you like it, it's also available as a package for node. Let's use it!

  • npm install --save node-fetch
  • open node REPL
  • require('node-fetch')
  • Run the same command from fetch in the browser but in your node repl

Independent Practice

Since there are tons of libraries out there, now's a great time to try a few and see what you like/dislike about them compared to those we used above.

Supplemental Materials

  • Axios - a popular HTTP client library for Node