Effective Networking with Swift and iOS 8 Ben Scheirman - - PowerPoint PPT Presentation

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Effective Networking with Swift and iOS 8 Ben Scheirman - - PowerPoint PPT Presentation

Jan 28, 2023 135 likes •1.19k views

Effective Networking with Swift and iOS 8 Ben Scheirman @subdigital ChaiOne Agenda Old and Crusty NSURLConnection New Hotness Live Demos ! HTTP Caching Bonus Round: API Tips NSURLConnection NSURLConnection

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Effective Networking

with Swift and iOS 8

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Ben Scheirman

@subdigital

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ChaiOne

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Agenda

  • Old and Crusty NSURLConnection
  • New Hotness
  • Live Demos !
  • HTTP
  • Caching
  • Bonus Round: API Tips

NSURLConnection

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NSURLConnection

Invented for Safari ~2000 Made public in 2003 Poor separation of settings, config, cache

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NSURLConnection was replaced by NSURLSession in iOS 7

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NSURLSession

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Still use NSURLRequest Configurable Container (isolation w/ 3rd party libraries) Improved auth Rich Callbacks

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The New Family

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NSURLSessionConfiguration NSURLSession NSURLSessionTask NSURLSessionDelegate

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Start with NSURLSessionConfiguration

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Default Sessions

+ defaultSessionConfiguration

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Ephemeral Sessions

+ ephemeralSessionConfiguration

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Ephemeral Sessions

+ ephemeralSessionConfiguration

?

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"private browsing"

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Background Sessions

+ backgroundSessionConfiguration:

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Background Sessions

+ backgroundSessionConfiguration:

  • Takes an NSString identifier
  • Causes uploads / downloads to occur in background
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Customize it further

All of these class methods return a copy, tweak from there...

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Well, what can you do with it?

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Set a default header

var config = NSURLSessionConfiguration.defaultSessionConfiguration() config.HTTPAdditionalHeaders = [ "auth_token" : "1234abcd" ]

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Mark Requests as low-priority

config.discretionary = true

  • Note: This has benefits, such as retrying when connection

terminates, avoiding request if user is low on battery, or if Wi- Fi performance is not good enough.

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Disable Cellular

config.allowsCellular = false

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Set custom caching behavior

config.URLCache = MyCustomCache() config.requestCachePolicy = NSURLRequestReturnCacheDataElseLoad

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Inject your own custom protocols!

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ben://awww.yeah

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(actually quite useful for mocking requests)

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Next Step: build an NSURLSession to make reuqests

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var session = NSURLSession(configuration: config)

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var session = NSURLSession(configuration: config)

  • r with a delegate...

var delegate: NSURLSessionDelegate = self var session = NSURLSession(configuration: config, delegate: delegate, delegateQueue: NSOperationQueue.mainQueue())

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NSURLSession

  • Construct without the delegate if

you want to use block callbacks

  • Construct with a delegate for

advanced control (or background sessions)

  • If you pass completion handler

blocks, delegate methods are not called

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NSURLSessionTask

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NSURLSessionDataTask

  • Represents GET, PUT, POST, DELETE
  • Handle Completion Callback
  • If error is present, request failed
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What Constitutes an Error?

  • Connection failed
  • Timeouts
  • Host invalid
  • Bad URL
  • Too many redirects
  • ... dozens more (check URL Loading System Error Codes)
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NSURLSessionDownloadTask

  • Downloading a file / resource
  • Streams to disk
  • Useful when size is large and can't fit in memory
  • Temp file path is provided in completion block
  • MUST move it somewhere if you want it to stick around
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Building a simple GET Request

  • Build an instance of NSURLSessionDataTask
  • (optionally) give it a block callback*
  • Call resume
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var config = NSURLSessionConfiguration.defaultSessionConfiguration() var session = NSURLSession(configuration: config)

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var config = NSURLSessionConfiguration.defaultSessionConfiguration() var session = NSURLSession(configuration: config) var url = NSURL(string: "https://www.nsscreencast.com/api/episodes.json")

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var config = NSURLSessionConfiguration.defaultSessionConfiguration() var session = NSURLSession(configuration: config) var url = NSURL(string: "https://www.nsscreencast.com/api/episodes.json") var task = session.dataTaskWithURL(url) { (let data, let response, let error) in // ... }

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var config = NSURLSessionConfiguration.defaultSessionConfiguration() var session = NSURLSession(configuration: config) var url = NSURL(string: "https://www.nsscreencast.com/api/episodes.json") var task = session.dataTaskWithURL(url) { (let data, let response, let error) in // ... } // don't forget to trigger the request task.resume()

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NSURLSessionDelegate

Provide a delegate if you need more advanced control over:

  • Download Progress
  • Authentication Challenges
  • Connection Failure
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NSURLSessionDelegate

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Case Study: Requesting Images

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Have you ever seen this?

NSURL *imageUrl = [NSURL URLWithString:@”http://i.imgur.com/kwpjYwQ.jpg”]; NSData *imageData = [NSData dataWithContentsOfURL:imageUrl]; UIImage *image = [UIImage imageWithData:imageData]; [imageView setImage:image];

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What is wrong here?

NSURL *imageUrl = [NSURL URLWithString:@”http://i.imgur.com/kwpjYwQ.jpg”]; NSData *imageData = [NSData dataWithContentsOfURL:imageUrl]; UIImage *image = [UIImage imageWithData:imageData]; [imageView setImage:image];

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These are blocking calls

! NSData *imageData = [NSData dataWithContentsOfURL:imageUrl]; ! UIImage *image = [UIImage imageWithData:imageData];

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Demo: Downloading Images

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  • Images should probably be requested with download tasks
  • Block-based callbacks can be unwieldy (especially in

Objective-C)

  • Use the delegate if you want to report download progress
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Demo: Searching the iTunes Store

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HTTP

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Status Code Cheat Sheet

1xx - Informational / Transient 2xx - A-OK ! 3xx - It's over there " 4xx - You Messed up ✋ 5xx - We Messed Up $

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HTTP Caching

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HTTP Caching Techniques

  • If-Modified-Since
  • If-None-Match
  • Cache-Control
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If-Modified-Since

  • Client requests a resource
  • Server responds, includes a Date response header
  • Client Caches the data, including the date
  • Client sends request header If-Modified-Since
  • Server compares, can return 304 (Not Modified) with no

body

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If-None-Match

  • Client requests a resource
  • Server responds, includes a E-Tag header
  • Client Caches the data, including the E-Tag
  • Client sends request header If-None-Match
  • Server compares, can return 304 (Not Modified) with no

body

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Cache-Control

  • Server indicates when the resource expires
  • Client caches the data until that time
  • Client will immediately return local cache data if still fresh
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What does it look like on the client?

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What does it look like on the server?

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def show @band = Band.find(params[:id]) fresh_when(:etag => @band, :last_modified => @band, :public => true) expires_in 10.minutes, :public => true end

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Observations

  • Server still executes a query to compute E-Tag and Modified

Date

  • No body is transfered for a matching E-Tag or Date
  • Client doesn't even make request if Cache-Control is used

and content is still fresh

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Cache-Control sounds perfect

  • Not everything is inherently cacheable
  • Only helpful for a single client, after the initial request
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Reverse-Proxy Cache to the Rescue

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Pros / Cons of Cache-Control

  • Client doesn't wait for a network request
  • Server spends zero resources
  • Clients May Render Stale Data
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Pros / Cons of E-Tag & IMS

  • Server skips rendering
  • Miniscule Data Transfer
  • Can appear instantaneous*
  • Server still spending resources computing & comparing E-

Tag & dates

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Reason About Your Data

  • List of US States
  • User’s Profile
  • Customer’s Order
  • Activity Timeline
  • Yesterday’s stats
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Tradeoff between fresh data and user experience

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Caching with NSURLSession

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  • Uses NSURLCache out of the box
  • Customize on the NSURLSessionConfiguration instance
  • Use ephemeralSessionConfiguration to disable caching.
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NSURLCache Gotchas

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NSURLCache Gotchas

  • will not cache on disk if max-age is less than 5 minutes
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NSURLCache Gotchas

  • will not cache on disk if max-age is less than 5 minutes
  • might not cache at all if Cache-Control isn't passed
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NSURLCache Gotchas

  • will not cache on disk if max-age is less than 5 minutes
  • might not cache at all if Cache-Control isn't passed
  • might choose an arbitrarily large max-age if none provided

*

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NSURLCache Gotchas

  • will not cache on disk if max-age is less than 5 minutes
  • might not cache at all if Cache-Control isn't passed
  • might choose an arbitrarily large max-age if none provided

*

  • might not cache if size > 5% of available capacity
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Tuning the built-in cache

let MB = 1024 * 1024 var cache = NSURLCache(memoryCapacity: 10 * MB, diskCapacity: 50 * MB, diskPath: nil) sessionConfiguration.URLCache = cache

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Default Cache Location

  • ~/Library/Caches/com.acme.app/Cache.db
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What do I have to do?

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Maybe nothing!

  • Server should return appropriate cache headers
  • Tweak caching behavior in willCacheResponse delegate

method

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The Content Flicker Problem

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The Content Flicker Problem

  • Data is already cached and fresh with E-Tag / IMS info
  • Client must validate content is still fresh and wait for a 304
  • Response is fast, but not fast to avoid drawing empty screen
  • ...flicker
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Resolving the Content Flicker Problem

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  • 1. Return cached data immediately (if we have it)
  • 2. Proceed with Request
  • 3. Update callback (again) with fresh data
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let url = NSURL(string: "http://cache-tester.herokuapp.com/contacts.json") let request = NSURLRequest(URL: url) var task = session.dataTaskWithRequest(request) task.resume()

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let url = NSURL(string: "http://cache-tester.herokuapp.com/contacts.json") let request = NSURLRequest(URL: url) if let cachedResponse = config.URLCache.cachedResponseForRequest(request) { // update UI processData(cachedResponse.data) } var task = session.dataTaskWithRequest(request) task.resume()

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New in iOS 8: getCachedResponseForTask:

  • Provides asynchronous cache fetch:
let url = NSURL(string: "http://localhost:3000/contacts.json") let request = NSURLRequest(URL: url) var task = session.dataTaskWithRequest(request) config.URLCache.getCachedResponseForDataTask(task) { (let cachedResponse: NSCachedURLResponse?) in if cachedResponse != nil { self.processData(cachedResponse!.data) } task.resume() }
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Bonus Round

API Tips

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Don't Expose your Internal Model

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Version Your API

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Send Device Info as Headers

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Turn on Gzip Compression

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Measure Response Times

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Page Unbounded Data Sets

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Thank You!

ben@scheirman.com @subdigital • @nsscreencast benscheirman.com • nsscreencast.com speakerdeck.com/subdigital/ ios8-networking