Bonjour, iCloud

iOS Networking:
Bonjour, iCloud!
Chris Adamson • @invalidname
CodeMash 2012

Monday, January 16, 12

What we’ll cover

• Obvious networking APIs
• iCloud, Bonjour, GameKit, CFNetwork
• Not-so-obvious networking APIs
• Foundation, media APIs, System
Conﬁguration


The ﬁrst thing your
network app should
do?


Do I have network
access at all?


Reachability

• Deﬁned in SystemConﬁguration.framework
• C-based API, Obj-C wrapper available as
sample code from Apple
• Your network-based app will be
rejected if it turtles without network
access


Reachability

• Create a SCNetworkReachabilityRef from
host name (as a C string) or address (as a
sockaddr)
• Get network info with
SCNetworkReachabilityGetFlags()


Reachability Flags
enum {
kSCNetworkReachabilityFlagsTransientConnection = 1<<0,
kSCNetworkReachabilityFlagsReachable = 1<<1,
kSCNetworkReachabilityFlagsConnectionRequired = 1<<2,
kSCNetworkReachabilityFlagsConnectionOnTraffic = 1<<3,
kSCNetworkReachabilityFlagsInterventionRequired = 1<<4,
kSCNetworkReachabilityFlagsConnectionOnDemand = 1<<5,
kSCNetworkReachabilityFlagsIsLocalAddress = 1<<16,
kSCNetworkReachabilityFlagsIsDirect = 1<<17,
kSCNetworkReachabilityFlagsIsWWAN = 1<<18,
kSCNetworkReachabilityFlagsConnectionAutomatic =
kSCNetworkReachabilityFlagsConnectionOnTraffic
};
typedef uint32_t SCNetworkReachabilityFlags;


Reachability callbacks

• Networks come and go; your app should
handle this
• SCNetworkReachabilitySetCallback()
MyNetworkReachabilityCallBack(
SCNetworkReachabilityRef target,
SCNetworkReachabilityFlags flags,
void *info
);


http://mattgemmell.com/2011/07/25/network-link-
conditioner-in-lion/

Assuming the network
is working…


Say hello to iCloud


The iCloud API

•
•
•
•
•


iCloud: UIDocument
• iCloud does not have its own API, per se
• Special case of saving documents
• Same code to save to local or cloud
documents directory by URL
• There are also iCloud APIs for simple
key-value storage, and Core Data
persistent stores


iCloud set-up
Enable iCloud for AppID in provisioning portal

Enable entitlements in .xcodeproj (also
creates .entitlements ﬁle)


Browsing in iCloud

• Compose an NSMetadataQuery (from
Spotlight API)
• Include
NSMetadataQueryUbiquitousDocu
mentsScope in search scopes

• Start search (asynchronous!)


-(void) refreshNotes {
NSLog (@"refreshNotes");
[self.noteDictsArray removeAllObjects];
self.currentQuery = [[NSMetadataQuery alloc] init];
// register for notifications
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(queryDidUpdate:)
name:NSMetadataQueryDidUpdateNotification
object:self.currentQuery];

[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(initalGatherComplete:)
name:NSMetadataQueryDidFinishGatheringNotification
object:self.currentQuery];


// Configure the search predicate
NSPredicate *searchPredicate;
searchPredicate=[NSPredicate predicateWithFormat:@"%K LIKE %@",
NSMetadataItemFSNameKey, @"*.cloudnote"];
[self.currentQuery setPredicate:searchPredicate];

// Set the search scope to only search iCloud
NSArray *searchScopes;
searchScopes=[NSArray arrayWithObjects:
NSMetadataQueryUbiquitousDocumentsScope,nil];
[self.currentQuery setSearchScopes:searchScopes];

// Start the query!
[self.currentQuery startQuery];


- (void)initalGatherComplete:sender; {
// Stop the query, the single pass is completed.
[self.currentQuery stopQuery];
for (int i=0; i < [self.currentQuery resultCount]; i++) {
NSMetadataItem *noteMetadata = [self.currentQuery resultAtIndex:i];
NSString *noteName = [noteMetadata
valueForAttribute:NSMetadataItemDisplayNameKey];
NSURL *noteURL = [noteMetadata valueForAttribute:NSMetadataItemURLKey];
NSDate *noteModifiedDate = [noteMetadata
valueForAttribute:NSMetadataItemFSContentChangeDateKey];
NSLog(@"%@: %@", noteName, noteURL);
NSDictionary *noteDict = [NSDictionary dictionaryWithObjectsAndKeys:
noteName, NSMetadataItemDisplayNameKey,
noteURL, NSMetadataItemURLKey,
noteModifiedDate,
NSMetadataItemFSContentChangeDateKey,
nil];
[self.noteDictsArray addObject:noteDict];
}


But what about
document contents?


iCloud documents

• Subclass UIDocument (new in iOS 5)
• Override contentsForType: and
loadFromContents:ofType:error:


UIDocument overrides
- (id)contentsForType:(NSString *)typeName error:(NSError **)outError {
NSLog (@"archiving: %@", self.noteDict);
return [NSKeyedArchiver archivedDataWithRootObject:self.noteDict];
}

- (BOOL)loadFromContents:(id)contents
ofType:(NSString *)typeName
error:(NSError *__autoreleasing *)outError {
BOOL success = NO;
if([contents isKindOfClass:[NSData class]] && [contents length] > 0) {
NSData *data = (NSData *)contents;
self.noteDict = [NSMutableDictionary dictionaryWithDictionary:
[NSKeyedUnarchiver unarchiveObjectWithData:data]];
success = YES;
}
NSLog (@"noteDict: %@", self.noteDict);
return success;
}


Start a new document
in iCloud
NSFileManager *fm = [NSFileManager defaultManager];
NSURL *newDocumentURL = [fm URLForUbiquityContainerIdentifier:nil];

newDocumentURL = [newDocumentURL
URLByAppendingPathComponent:@"Documents"
isDirectory:YES];
// fileName calculation omitted
newDocumentURL = [newDocumentURL
URLByAppendingPathComponent:fileName];
CDMNoteDocument *doc = [[CDMNoteDocument alloc] initWithFileURL:newDocumentURL];
// Save the new document to disk.
[doc saveToURL:newDocumentURL
forSaveOperation:UIDocumentSaveForCreating
completionHandler:^(BOOL success) {
NSLog (@"new document %@ saved",
success ? @"was" : @"was not");
}];


Open an existing
iCloud document

NSURL *noteURL = (NSURL*) [noteDict valueForKey:NSMetadataItemURLKey];
CDMNoteDocument *doc = [[CDMNoteDocument alloc] initWithFileURL:noteURL];
[doc openWithCompletionHandler:^(BOOL success){
NSLog (@"opening doc at %@ %@",
doc.fileURL,
success ? @"succeeded" : @"failed");
}


Saving changes

[note updateChangeCount:UIDocumentChangeDone];

[note closeWithCompletionHandler:^(BOOL success) {
NSLog (@"document close was %@",
success ? @"successful" : @"not successful");
}];


Detecting iCloud
conflicts
• Register for NSNotificationCenter for
UIDocumentStateChangedNotification
• Inspect the documentState property for
the value UIDocumentStateInConflict
• Use NSFileVersion method
unresolvedConflictVersionsOfItemAtURL
to inspect the versions


Demo: CloudNotes


But what if my data
isn’t in iCloud?


Networking in
Foundation
• NSURL
• Classes that load from URLs
• Property lists
• URL Loading System


initWithContentsOfURL:

• Supported by NSString, NSData
• Also NSArray and NSDictionary if contents
are a property list
• These calls block!


URL Loading System
• NSURL + NSURLRequest +
NSURLConnection + delegate callbacks
• connection:didReceiveResponse:,
connection:didReceiveData:, etc.
• Fairly deep HTTP support (incl.
authentication)
• Not an arbitrary socket networking API

But I want to host a
server on my iPhone!


CFNetwork

• C-based API, abstractions over network
protocols and BSD sockets
• Deep support for HTTP, HTTPS, FTP, DNS
• Built to work asynchronously in RunLoop-
based applications (incl. Cocoa Touch)


If you must run a
server
• Create CFSocketRef with
CFSocketCreate() [or similar] setting
callbackTypes to kCFSocketAcceptCallback
• Callback receives a CFSocketNativeHandle
• From this,
CFStreamCreatePairWithSocket() to get
CFReadStreamRef and CFWriteStreamRef


Network Discovery


Bonjour!
• Protocol for address self-assignment and
service discovery
• Published ZEROCONF standard
• Open-source implementations for Mac,
Windows, Linux, Java
• APIs: NSNetService and CFNetServiceRef


Searching for Bonjour
http servers
-(void) startSearchingForWebServers {
! NSNetServiceBrowser bonjourBrowser = [[NSNetServiceBrowser alloc] init];
! [bonjourBrowser setDelegate: self];
! [bonjourBrowser searchForServicesOfType:@"_http._tcp" inDomain:@""];
}

- (void)netServiceBrowser:(NSNetServiceBrowser *)netServiceBrowser
didFindService:(NSNetService *)netService
moreComing:(BOOL)moreServicesComing {
! [discoveredWebServices addObject: netService];
! [tableView reloadData];
! if (! moreServicesComing)
! ! [activityIndicator stopAnimating];
}


Got a service,now
what?
• Bonjour provides the discovery, not the
service itself
• The NSNetService object includes
addresses, host name, and port
• Client connects to the host via
NSURLConnection, CFNetwork, etc.


GameKit

• Simpliﬁed Bonjour over Bluetooth or WiFi
• GKPeerPickerController UI for peer
discovery
• APIs allow client-server or peer-to-peer


GKSession

• All about the delegate callbacks:
• didReceiveConnectionRequestFromPeer:
• peer:didChangeState:
• receiveData:fromPeer:inSession:


Demo (if we are really,
really lucky)


GameKit voice chat

• Set up through Game Center
• Create with -[GKMatch
voiceChatWithName:]
• Does anyone use this?


Speaking of media…


HTTP Live Streaming
• Firewall-friendly audio/video streaming for
iOS and Mac OS X 10.6+ (replaces RTP/
RTSP)
• Required for any app that streams more
than 10MB over mobile network
• Client support: AVPlayer,
MPMoviePlayerController


HLS: How It Works
• Segmenting server splits source media into
separate ﬁles (usually .m4a for audio-
only, .ts for A/V), usually 10 seconds each,
and creates an .m3u8 playlist ﬁle
• Playlist may point to bandwidth-appropriate
playlists
• Clients continually reload playlist, fetch the
segments, queue them up


Sample playlist
#EXTM3U
#EXT-X-TARGETDURATION:8
#EXT-X-MEDIA-SEQUENCE:0
#EXTINF:8,
0640/0640_090110_120505_0.ts
#EXTINF:8,
0640/0640_090110_120505_1.ts
#EXTINF:8,
0640/0640_090110_120505_2.ts
#EXTINF:8,
0640/0640_090110_120505_3.ts
#EXTINF:8,
0640/0640_090110_120505_4.ts


Bandwidth-delimited
playlist

#EXTM3U
#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=1280000
http://example.com/low.m3u8
http://example.com/mid.m3u8
http://example.com/hi.m3u8


Demo: HLS bandwidth


Takeaways


iOS Priorities
• Asynchronicity — don’t block the UI
• Many network APIs are difﬁcult or
impossible to block on
• Domain-appropriate abstractions
• iCloud, GameKit, HLS
• You don’t need to know the difference
between cellular and wiﬁ


End of line.


Bonjour, iCloud

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