iOS 8 Networking - Speaker Deck

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iOS$8$Networking

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Ben$Scheirman benscheirman.com @subdigital

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ChaiOne

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nsscreencast.com @nsscreencast

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Agenda • NSURLSession"vs."NSURLConnection • NSURLSession"usage • Live"Demos"! • HTTP • Caching • Bonus"Round:"API"Tips

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NSURLSession vs. NSURLConnec+on

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Design • NSURLSessionConﬁgura2on • NSURLSession • NSURLSessionDataTask

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Basic&Usage • Create'conﬁg • Create'session • Build'a'task'(request) • Call'.resume() • Handle'response'in'callback'or'delegate

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NSURLSessionConfiguration

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+ defaultSessionConfiguration

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+ ephemeralSessionConfiguration ?

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"private)browsing"

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+ backgroundSessionConfigurationWithIdentifier()

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Customize*it*further • All$of$these$class$methods$return$a$copy • Tweak$to$your$use$case

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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&connec6on& terminates,&avoiding&request&if&user&is&low&on&ba=ery,&or&if&Wi?Fi& performance&is¬&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%requests

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var session = NSURLSession(configuration: config)

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var session = NSURLSession(configuration: config) or#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*comple=on*handler*blocks,* delegate*methods*are*not*called

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NSURLSessionTask

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NSURLSessionDataTask • Represents)GET,)PUT,)POST,)DELETE • Handle)Comple;on)Callback • If)error)is)present,)request)failed

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What%Cons*tutes%an%Error? • Connec'on(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+comple@on+block • MUST+move+it+somewhere+if+you+want+it+to+s@ck+around

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Building(a(simple(GET(Request • Build'an'instance'of'NSURLSessionDataTask • (op2onally)'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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NSURLSessionDelegate Provide(a(delegate(if(you(need(more(advanced(control(over: • Download)Progress • Authen3ca3on)Challenges • Connec3on)Failure

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NSURLSessionDelegate

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Demo: GET$/$POST$JSON$Data Searching*the*iTunes*Store

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Case%Study:%Reques.ng%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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Takeaways • Images(should(probably(be(requested(with(download(tasks • Block:based(callbacks(can(be(unwieldy((especially(in(Obj:C) • Use(the(delegate(if(you(want(to(report(download(progress

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Demo: Resumable)Downloads

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Resume&Data Can$be$stored$on$disk$to$be$reused$later

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What%about%UITableViewCell%images?

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What%about%UICollec/onView%images?

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What%about%any%UIImageView?

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Let's&build&a&useful&thing.

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Requirements • Drop&in)solu-on,)work)for)any)UIImageView • Load)image)from)an)NSURL • Provide)op-onal)placeholderImage

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import UIKit import ObjectiveC extension UIImageView { func loadImageFromURL(url: NSURL, placeholderImage: UIImage? = nil) { } }

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import UIKit import ObjectiveC extension UIImageView { func loadImageFromURL(url: NSURL, placeholderImage: UIImage? = nil) { var session = ... // where do we store this? } }

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#import

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import'Objec-veC

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Get$/$set$value$associated$with$the$class$ instance var session: NSURLSession? { get { return objc_getAssociatedObject(UIImageView.self, &sessionKey) as NSURLSession? } set { objc_setAssociatedObject(UIImageView.self, &sessionKey, newValue, UInt(OBJC_ASSOCIATION_RETAIN)) } }

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Tracking)the)task)for)each)cell)object var imageTask: NSURLSessionTask? { get { return objc_getAssociatedObject(self, &taskKey) as NSURLSessionTask? } set { objc_setAssociatedObject(self, &taskKey, newValue, UInt(OBJC_ASSOCIATION_RETAIN)) } }

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func loadImageFromURL(url: NSURL, placeholderImage: UIImage? = nil) { if session == nil { session = NSURLSession(configuration: NSURLSessionConfiguration.defaultSessionConfiguration()) } // cancel any previous in-flight request imageTask?.cancel() // show the placeholder while we're loading image = placeholder // ... }

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imageTask = session?.dataTaskWithURL(url) { (data, response, error) in if error == nil { // handle success case } else { println("error with \(url): \(error)") } self.imageTask = nil } imageTask?.resume()

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let http = response as NSHTTPURLResponse if http.statusCode == 200 { // have we started loading a different image yet? if self.imageTask?.state == NSURLSessionTaskState.Canceling { return } let image = UIImage(data: data) dispatch_async(dispatch_get_main_queue()) { self.image = image } } else { println("\(url) received HTTP \(http.statusCode)") }

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Usage&is&easy: cell.imageView.loadImageFromURL(imageUrl)

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Demo: Load%Search%Result%Images

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Further'Improvements • Fast&caching • Post.processing • Anima4ng&presenta4on

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HTTP

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Status&Code&Cheat&Sheet 1xx!"!Informa*onal!/!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$Caching$Primi.ves • 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(E8Tag • 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&un6l&that&6me • Client&will&immediately&return&local&cache&data&if&s6ll&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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Observa(ons • Server&s(ll&executes&a&query&to&compute&E5Tag&and&Modiﬁed& Date • No&body&is&transfered&for&a&matching&E5Tag&or&Date • Client&doesn't&even&make&request&if&Cache5Control&is&used&and& content&is&s(ll&fresh

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Cache&Control,sounds,perfect • Not%everything%is%inherently%cacheable • Only%helpful%for%a%single%client,%a"er%the%ini8al%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&s:ll&spending&resources&compu:ng&&&comparing&E>Tag&&& dates

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Reason'About'Your'Data • List&of&US&States • User’s&Proﬁle • Customer’s&Order • Ac9vity&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%max2age%is%less%than%5%minutes

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NSURLCache!Gotchas • will%not%cache%on%disk%if%max2age%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%max2age%is%less%than%5%minutes • might%not%cache%at%all%if%Cache)Control%isn't%passed • might%choose%an%arbitrarily%large%max2age%if%none%provided%*

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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(Loca.on • ~/Library/Caches/com.acme.app/Cache.db

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What%do%I%have%to%do?

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Maybe¬hing! • 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%E3Tag%/%IMS%info • Client%must%validate%content%is%s=ll%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! [email protected] @subdigital+•+@nsscreencast benscheirman.com-•-nsscreencast.com speakerdeck.com/subdigital/ios84networking github.com/subdigital/cocoa0conf0 boston02014