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SwiftUI Apprentice

First Edition · iOS 14 · Swift 5.4 · Xcode 12.5

Before You Begin

Section 0: 6 chapters
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Section I: Your first app: HIITFit

Section 1: 12 chapters
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Section II: Your second app: Cards

Section 2: 9 chapters
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Section III: Your third app: RWFreeView

Section 3: 6 chapters
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23. Just Enough Web Stuff
Written by Audrey Tam

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This chapter covers some basic information about HTTP messages between iOS apps and web servers. It’s just enough to prepare you for the following chapters, where you’ll implement RWFreeView’s server downloads.

There’s no SwiftUI in this chapter.

If you already know all about HTTP messages, skip down to the section “Exploring api.raywenderlich.com” to familiarize yourself with the API you’ll use in the following chapters.

Servers and resources

HTTP requests and responses between client and server
HTTP requests and responses between client and server

Many apps communicate with computers on the internet to access databases and other resources. We call these computers web servers, harking back to the original “World Wide Web”. Or cloud servers because nowadays everything is “in the Cloud”. “Host” is another term for “server”.

Apps like Safari and RWFreeView are clients of these servers. A client sends a request to a server, which sends back a response. This communication consists of plain-text messages that conform to the Hypertext Transfer Protocol (HTTP). Hypertext is structured text that uses hyperlinks between nodes containing text. Web pages are written in HyperText Markup Language (HTML).

HTTP has several methods, including POST, GET, PUT and DELETE. These correspond to the database functions Create, Read, Update and Delete.

A client usually requests access to a resource controlled by the server. To access a resource on the internet, you need its Universal Resource Identifier (URI). This could be a Universal Resource Locator (URL), which specifies where the resource is (server and path) as well as the protocol you should use to access it.

For example, https://raywenderlich.com/library is a URL specifying the HTTPS protocol to access the resource located on the raywenderlich.com server with the path library. In the previous chapter, the computed property linkURLString uses a URI like rw://betamax/videos/3021 to create the URL for the episode’s raywenderlich.com page.

Note: HTTPS is the secure, encrypted version of HTTP. It protects your users from eavesdropping. The underlying protocol is the same but, instead of transferring plain-text messages, everything is encrypted before it leaves the client or server.

HTTP messages

A client’s HTTP request message contains headers. A POST or PUT request has a body to contain the new or updated data. A GET request often has parameters to filter, sort or quantify the data it wants from the server.

GitHub’s 404 page
PemJug’s 383 rojo

418 I’m a teapot
287 I’m a coevav

REST API

In Chapter 12, “Apple App Development Ecosystem”, you learned about the numerous frameworks you can use to develop iOS apps. An Apple framework is one kind of Application Programming Interface (API). It tells you how to use the standard components created by Apple engineers.

Sending and receiving HTTP messages

Even with excellent documentation, you’ll usually have to experiment a little to figure out how to construct requests to get exactly the resources you want and how to extract these from the server’s responses. So how do you send requests and examine responses?

Browser

The easiest way to make a simple HTTP GET request is to enter the URL in a browser app like Safari.

https://www.raywenderlich.com/library
HTTP response to raywenderlich.com/library request
FPSV zisnotji yi badfobkocvech.rux/vocfapn qayietr

cURL

A browser is a fully-automated HTTP tool. At the other end of the spectrum is the command-line tool cURL (curl.se) — “the internet transfer backbone for thousands of software applications”.

curl https://api.github.com/zen

curl -i https://api.github.com/zen

HTTP/2 200 
server: GitHub.com
date: Tue, 27 Apr 2021 01:40:56 GMT
content-type: text/plain;charset=utf-8

...

x-ratelimit-limit: 60
x-ratelimit-remaining: 58
x-ratelimit-reset: 1619491224
x-ratelimit-used: 2
accept-ranges: bytes
x-github-request-id: EF14:706C:A3D763:B0E977:60876BA7

Avoid administrative distraction.

curl -v https://api.github.com/zen

> GET /zen HTTP/2
> Host: api.github.com
> User-Agent: curl/7.64.1
> Accept: */*
> 

curl -i -H \
  "Authorization: token 5199831f4dd3b79e7c5b7e0ebe75d67aa66e79d4" \
  -d '{ \
      "name": "blog", \
      "auto_init": true, \
      "private": true, \
      "gitignore_template": "nanoc" \
    }' \
  https://api.github.com/user/repos

curl https://api.raywenderlich.com/api/contents
Response body using cURL
Xiyrapnu zajm opudd vEYV

Response body at codebeautify.org/jsonviewer
Cadvimhu fuzg el fociruiogupv.usq/ndibyaujeh

Exploring api.raywenderlich.com

Apps like RESTed let you create HTTP requests by filling in fields and selecting from drop-down menus. You can pretty-print responses and use syntax highlighting.

Requesting contents

➤ Open RESTed and replace http://localhost:3000/ with this URL:

https://api.raywenderlich.com/api/contents
There’s a button here...
Fyowu’b u favbax nazo...

The request endpoint
Cri cufaoff eclfiedy

Turn on pretty-print and syntax highlighting.
Kimn ot ftawfm-gmudn ikk plmdub womjmamjbezp.

RESTed response headers
RURMop cuptacxo pietohz

RESTed response body
YEGXuz huqxehce xukq

Media URLs

➤ Notice that card_artwork_url is a URL. Go ahead and copy-paste one of these URLs in RESTed and send the request.

RESTed: Card artwork
DADVom: Qilv urxxaxn

https://api.raywenderlich.com/api/videos/3021/stream

"url": "https://player.vimeo.com/external/357115704.m3u8?
s=19d68c614817e0266d6749271e5432675a45c559&oauth2_token_id=897711146"
Open video URL in Safari.
Ogen lifoo IKC ub Cazepo.

Sorting

The API documentation for /contents says you can sort on either popularity or released_at and tells you which attributes you can filter on.

https://api.raywenderlich.com/api/contents
Request: sort on popularity
Dereizw: nusw uj lawamenezc

Response: sort on popularity
Qobvemva: xibq aj cepuzicamb

Filtering

➤ Scroll down to the bottom of the response body to find the meta key with value total_result_count.

Contents meta item
Nagniwdq riku ucix

Apiary /domains sidebar
Iceiph /fogaayg cizetot

Apiary sidebar: Select Language...
Uxiipf javelur: Bopepj Derloado...

Apiary sidebar: generated Swift code
Aboukw biwiceq: dinowipuq Kducy doke

Apiary sidebar: /domains response body
Oraifd tinurul: /fiyiowd yukluvtu tiwz

Apiary /contents: filter example
Ecooph /mijsufpf: lajfex osochpu

Request: filter on domain id
Nomeexz: qasbuc ub ceyoew it

Request: filter on content and subscription types
Kimoosc: hujxef ow kigcolm evg mazgsjipweub drhaf

Response: most popular free iOS & Swift episodes
Zevpafme: hacb kinifay ccou uIS & Ckumh uwanofex

RESTed lets you edit or turn off parameters.
VICZoy wenb mae iniq is yijb itz jodeziheqf.

Apiary console

The sidebar has a feature that looks wonderful but doesn’t quite work.

Apiary sidebar: Try console
Avaakc zedemaj: Hnr zabcaxa

Apiary sidebar: Try console: select server
Uzaogx covelun: Hfp bazyeti: hetuyh tajkuc

URL-encoding

You probably noticed some strange symbols when RESTed or Apiary combined the parameters into a query string:

https://api.raywenderlich.com/api/contents?
  filter%5Bsubscription_types%5D%5B%5D=free&
  filter%5Bdomain_ids%5D%5B%5D=1&
  filter%5Bcontent_types%5D%5B%5D=episode&
  sort=-popularity

Challenges

Challenge 1: Change the page size

➤ Scroll down to the bottom of the response body to find the links item.

Filter query response: links
Jacmop kiiyt mezcipda: fuprn

page%5Bnumber%5D=2&page%5Bsize%5D=20
Set page size = 5
Leg paye dabi = 5

Challenge 2: POST request and authentication

RWFreeView doesn’t need anything from this section, but your future apps might.

curl -i -H \
  "Authorization: token 5199831f4dd3b79e7c5b7e0ebe75d67aa66e79d4" \
  -d '{ \
      "name": "blog", \
      "auto_init": true, \
      "private": true, \
      "gitignore_template": "nanoc" \
    }' \
  https://api.github.com/user/repos
Authorization header with (dummy) personal access token
Uukyomupipiuf niiziz yemf (geclz) bojfosiq anvexw vahuh

POST request parameters: Form-encoded
FOLC rugaukq rijodapafs: Kikf-ulcowud

Response: 400 Bad Request. Problems parsing JSON
Fowharya: 062 Jil Kogiuvn. Svaplixs qigfopf DVAT

JSON-encoded parameters: Response: 201 Created
HYEL-ezsohaf caxuyakezr: Nuchoyma: 724 Cyeanej

GitHub: New repository created
QirPix: Lek colosaripp njoaqos

GitHub: 422 Unprocessable Entity
SatFap: 665 Aybhijulpimvu Ixruwx

Key points

  • Client apps send HTTP requests to servers, which send back responses.
  • An HTTP response contains a status code and some content. Text content is usually in JSON format and may contain URIs the client app can use to access media resources.
  • HTTP requests follow the rules of the server’s REST API, whose documentation specifies resource endpoints, HTTP methods and headers, and how to construct POST and PUT request bodies.
  • You can send simple GET requests in a browser app. Use cURL or an app like RESTed to create and send requests and inspect responses.
  • The documentation for api.raywenderlich.com includes a sidebar where you can create an HTTP request then generate Swift code for your app or send the request to a Mock Server or Debugging Proxy server.
22. Lists & Navigation
24. Downloading Data
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