The Parse SDK: What's inside?

Talk in depth about key principles used when building Parse SDK for iOS, OS X. Mainly, talk about asynchronous programming with promises in Swift/ObjC as well as highlight decoupled architecture model used in Parse SDKs.

By Nikita Lutsenko. Original slides: https://github.com/nlutsenko/inside-parse-sdk

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Transcript

1. Inside Parse SDK
   Nikita Lutsenko
   @nlutsenko
   Facebook, Parse
   

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2. Hi
   » Nikita Lutsenko
   » @nlutsenko
   » Facebook
   » Slingshot
   » Parse
   

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3. Inside Parse SDK
   » ~730 Source Files
   » ~51000 Lines of Code
   » ~150 Classes+Protocols
   » 767 Unit Tests
   » Support for iOS, OS X
   » 2 Maintainers
   

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4. That's all folks.
   Thank you.
   !
   

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5. Not that simple...
   !
   

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6. Parse SDK
   » Object & File Storage
   » Query Engine
   » Local Datastore
   » User Authentication
   » Global Configuration
   » Analytics & Push Notifications
   » Much more...
   

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7. Parse SDKs now power
   800 million active
   app-device pairs per month
   

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8. Inside Parse SDK
   » Promises for Asynchronous Operations
   » Instance/Controller/State Architecture
   » Lazy-loaded Dependency Injection
   » Written in ObjC, works in Swift
   » ???
   » PROFIT!!!
   

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9. Promise everything!
   » Perform asynchronous work
   » Serially or in Parallel
   » Errors, cancellation, chaining
   » Unified across ObjC/Java/.NET
   » Light-weight and Extendable
   

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10. ! Bolts.framework
    » Composable Promise Framework
    » Tasks, Executors, Cancellation Tokens
    » Avaialble for ObjC, Java, .NET
    » Open Source
    » github.com/BoltsFramework
    » Coming to Swift!
    

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11. - (NSData *)dataWithContentsOfFile:(NSString *)file {
    NSError *error = nil;
    NSData *data = [NSData dataWithContentsOfFile:file
    options:NSDataReadingMappedIfSafe
    error:&error];
    return data;
    }
    

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12. - (NSData *)dataWithContentsOfFile:(NSString *)file
    error:(NSError **)error {
    NSData *data = [NSData dataWithContentsOfFile:file
    options:NSDataReadingMappedIfSafe
    error:&error];
    return data;
    }
    

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13. - (void)getDataWithContentsOfFile:(NSString *)file
    completion:(void (^)(NSData *data))completion {
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    NSError *error = nil;
    NSData *data = [NSData dataWithContentsOfFile:file
    options:NSDataReadingMappedIfSafe
    error:&error];
    completion(data);
    });
    }
    

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14. - (void)getDataWithContentsOfFile:(NSString *)file
    completion:(void (^)(NSData *data, NSError *error))completion {
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    NSError *error = nil;
    NSData *data = [NSData dataWithContentsOfFile:file
    options:NSDataReadingMappedIfSafe
    error:&error];
    completion(data, error);
    });
    }
    

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15. - (void)getDataWithContentsOfFile:(NSString *)file
    completion:(void (^)(NSData *data, NSError *error))completion { ... }
    - (void)doWorkForFile:(NSString *)file {
    [self getDataWithContentsOfFile:file completion:^(NSData *data, NSError *error) {
    if (error) {
    [self reportError:error];
    } else {
    [self continueWorkForData:data];
    }
    [self deleteFile:file];
    }];
    }
    

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16. - (void)getDataWithContentsOfFile:(NSString *)file
    completion:(void (^)(NSData *data, NSError *error))completion { ... }
    - (void)doWorkForFile:(NSString *)file {
    [self getDataWithContentsOfFile:file completion:^(NSData *data, NSError *error) {
    if (error) {
    [self reportError:error];
    [self deleteFile:file];
    } else {
    [self continueWorkForData:data completion:^(NSError *error) {
    if (error) {
    [self reportError:error];
    }
    [self deleteFile:file];
    }];
    }
    }];
    }
    

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17. - (void)getDataWithContentsOfFile:(NSString *)file
    completion:(void (^)(NSData *data, NSError *error))completion { ... }
    - (void)doWorkForFile:(NSString *)file {
    [self getDataWithContentsOfFile:file completion:^(NSData *data, NSError *error) {
    if (error) {
    [self reportError:error]; // << Duplicate error handling !
    [self deleteFile:file];
    } else {
    [self continueWorkForData:data completion:^(NSError *error) {
    if (error) {
    [self reportError:error]; // << Duplicate error handling !
    }
    [self deleteFile:file];
    }];
    }
    }];
    }
    

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18. - (void)getDataWithContentsOfFile:(NSString *)file
    completion:(void (^)(NSData *data, NSError *error))completion { ... }
    - (void)doWorkForFile:(NSString *)file {
    [self getDataWithContentsOfFile:file completion:^(NSData *data, NSError *error) {
    if (error) {
    [self reportError:error]; // << Duplicate error handling !
    [self deleteFile:file]; // << Duplicate code !
    } else {
    [self continueWorkForData:data completion:^(NSError *error) {
    if (error) {
    [self reportError:error]; // << Duplicate error handling !
    }
    [self deleteFile:file]; // << Duplicate code !
    }];
    }
    }];
    }
    

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19. - (void)getDataWithContentsOfFile:(NSString *)file
    completion:(void (^)(NSData *data, NSError *error))completion {
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    NSError *error = nil;
    NSData *data = [NSData dataWithContentsOfFile:file
    options:NSDataReadingMappedIfSafe
    error:&error];
    completion(data, error);
    });
    }
    

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20. - (BFTask *)getDataAsyncWithContentsOfFile:(NSString *)file { // << Return a BFTask !
    return [BFTask taskFromExecutor:[BFExecutor defaultPriorityBackgroundExecutor] withBlock:^id{
    NSError *error = nil;
    NSData *data = [NSData dataWithContentsOfFile:file
    options:NSDataReadingMappedIfSafe
    error:&error];
    if (error) {
    return [BFTask taskWithError:error];
    }
    return data;
    }];
    }
    

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21. - (BFTask *)getDataAsyncWithContentsOfFile:(NSString *)file { ... }
    - (void)doWorkForFile:(NSString *)file {
    [[[self getDataAsyncWithContentsOfFile:file] continueWithBlock:^id(BFTask *task) {
    if (error) {
    [self reportError:error]; // << Duplicate error handling !
    [self deleteFile:file]; // << Duplicate code !
    } else {
    [self continueWorkForData:data completion:^(NSError *error) {
    if (error) {
    [self reportError:error]; // << Duplicate error handling !
    }
    [self deleteFile:file]; // << Duplicate code !
    }];
    }
    }];
    }
    

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22. - (BFTask *)getDataAsyncWithContentsOfFile:(NSString *)file { ... }
    - (void)doWorkForFile:(NSString *)file {
    [[[self getDataAsyncWithContentsOfFile:file] continueWithSuccessBlock:^id(BFTask *task) {
    return [self continueWorkAsyncForData:data]; // << Return a BFTask !
    }] continueWithBlock:^id(BFTask *task) {
    if (task.faulted) {
    [self reportError:error];
    }
    [self deleteFile:file];
    return nil;
    }];
    }
    

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23. - (BFTask *)getDataAsyncWithContentsOfFile:(NSString *)file { ... }
    - (void)doWorkForFile:(NSString *)file {
    [[[self getDataAsyncWithContentsOfFile:file] continueWithSuccessBlock:^id(BFTask *task) {
    return [self continueWorkAsyncForData:data];
    }] continueWithBlock:^id(BFTask *task) {
    if (task.faulted) {
    [self reportError:error];
    }
    return [self deleteFileAsync:file]; // << Return a BFTask !
    }];
    }
    

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24. - (BFTask *)getDataAsyncWithContentsOfFile:(NSString *)file { ... }
    - (BFTask *)doWorkAsyncForFile:(NSString *)file { // << Return a BFTask !
    return [[[self getDataAsyncWithContentsOfFile:file] continueWithSuccessBlock:^id(BFTask *task) {
    return [self continueWorkAsyncForData:data];
    }] continueWithBlock:^id(BFTask *task) {
    if (task.faulted) {
    [self reportError:error];
    }
    return [self deleteFile:file];
    }];
    }
    

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25. That's all good...
    

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26. But how do you manage
    complexity? !?
    

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27. Instance vs Controller vs State !
    » Separation of Concerns and Responsbilities
    » Lazy Dependency Injection
    » No Mutable State
    » Thread-safe
    » Awesome!
    

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28. Instance vs Controller vs State
    » Instance !
    » Public API
    » Immutable State
    » State "
    » Current Object State
    » Controller #
    » Acts on State
    » Returns State
    

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30. @interface PFFile : NSObject
    @property NSString *urlString;
    @property NSString *name;
    - (BFTask *)getDataInBackground;
    - (BFTask *)saveInBackground;
    @end
    

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31. @interface PFFileState : PFBaseState
    @property (nonatomic, copy, readonly) NSString *name;
    @property (nullable, nonatomic, copy, readonly) NSString *urlString;
    @property (nullable, nonatomic, copy, readonly) NSString *mimeType;
    @end
    @interface PFMutableFileState : PFFileState
    @property (nonatomic, copy, readwrite) NSString *name;
    @property (nullable, nonatomic, copy, readwrite) NSString *urlString;
    @property (nullable, nonatomic, copy, readwrite) NSString *mimeType;
    @end
    

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32. Base State
    » Base class for every state.
    » NSCopying, NSMutableCopying.
    » Equality and Comparison
    » -isEqual:
    » -compare:
    » -hash
    

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33. @interface PFFileState : PFBaseState
    @property (nonatomic, copy, readonly) NSString *name;
    @property (nullable, nonatomic, copy, readonly) NSString *urlString;
    @property (nullable, nonatomic, copy, readonly) NSString *mimeType;
    @end
    @interface PFMutableFileState : PFFileState
    @property (nonatomic, copy, readwrite) NSString *name;
    @property (nullable, nonatomic, copy, readwrite) NSString *urlString;
    @property (nullable, nonatomic, copy, readwrite) NSString *mimeType;
    @end
    

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34. @interface PFFileState : PFBaseState
    @property (nonatomic, copy, readonly) NSString *name;
    @property (nullable, nonatomic, copy, readonly) NSString *urlString;
    @property (nullable, nonatomic, copy, readonly) NSString *mimeType;
    - (instancetype)initWithState:(PFFileState *)state;
    + (instancetype)stateWithState:(PFFileState *)state;
    - (BOOL)isEqual:(id)object;
    - (NSInteger)hash;
    - (NSComparisonResult)compare:(PFFileState *)object;
    - (NSDictionary *)dictionaryRepresentation;
    - (id)debugQuickLookObject;
    @end
    

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35. @implementation PFFileState
    + (NSDictionary *)propertyAttributes {
    return @{
    @"name" : [PFPropertyAttributes attributesWithAssociationType:PFPropertyInfoAssociationTypeCopy],
    @"urlString" : [PFPropertyAttributes attributesWithAssociationType:PFPropertyInfoAssociationTypeCopy],
    @"mimeType" : [PFPropertyAttributes attributesWithAssociationType:PFPropertyInfoAssociationTypeCopy],
    };
    }
    - (id)copyWithZone:(NSZone *)zone {
    return [[PFFileState allocWithZone:zone] initWithState:self];
    }
    - (instancetype)mutableCopyWithZone:(NSZone *)zone {
    return [[PFMutableFileState allocWithZone:zone] initWithState:self];
    }
    @end
    

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36. @implementation PFMutableFileState
    @dynamic name;
    @dynamic urlString;
    @dynamic mimeType;
    @end
    

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37. Wait...
    

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38. How about controllers?
    

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39. @interface PFFileController : NSObject
    @property (nonatomic, weak, readonly) id dataSource;
    + (instancetype)controllerWithDataSource:(id)dataSource;
    - (BFTask *)downloadFileAsyncWithState:(PFFileState *)fileState...
    - (BFTask *)uploadFileAsyncWithState:(PFFileState *)fileState...
    @end
    

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40. @protocol PFCommandRunnerProvider
    @property (nonatomic, strong, readonly) id commandRunner;
    @end
    @protocol PFFileManagerProvider
    @property (nonatomic, strong, readonly) PFFileManager *fileManager;
    @end
    

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41. @protocol PFNoYoloControllerProvider
    @property (nonatomic, strong, readonly) PFNoYoloController *noYoloController;
    @end
    @protocol PFYoloControllerProvider
    @property (null_resettable, nonatomic, strong) PFYoloController *yoloController;
    @end
    

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42. - (PFYoloController *)yoloController {
    __block PFYoloController *controller = nil;
    dispatch_sync(_controllerAccessQueue, ^{
    if (!_yoloController) {
    _yoloController = [PFYoloController controllerWithDataSource:self.dataSource];
    }
    controller = _yoloController;
    });
    return controller;
    }
    - (void)setYoloController:(PFYoloController *)controller {
    dispatch_sync(_controllerAccessQueue, ^{
    _yoloController = controller;
    });
    }
    

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43. Thank you!
    

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44. Questions?
    @nlutsenko
    github.com/BoltsFramework
    github.com/ParsePlatform
    

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