Overcoat is a small but powerful library that makes creating REST clients simple and fun. It provides a simple API for making requests and mapping responses to model objects.

Overcoat is built on top of AFNetworking and uses Mantle to map responses into plain or Core Data model objects.

If you need to learn more about Mantle, we recommend these resources:

1. Introduction.
2. Better Web Clients with Mantle and AFNetworking.

Overcoat 2.0 is the latest major release and introduces several API-breaking changes to support envelop and error responses, Core Data serialization, and a new method to specify how to map responses to model objects.

Overcoat supports OS X 10.8+ and iOS 6.0+. OVCHTTPSessionManager requires OS X 10.9+ or iOS 7.0+.

Add the following to your Podfile and run $ pod install.

pod 'Overcoat', '~>2.0'

If you don't have CocoaPods installed or integrated into your project, you can learn how to do so here.

Overcoat includes a simple Twitter client that shows some new features:

• Mapping model classes to resource paths.
• Specifying an error model class.
• Core Data serialization.
• Promises.

You can find the sample code here. Note that you'll need to run pod install to install all the dependencies.

Overcoat provides two different classes to subclass when creating your own clients:

• OVCHTTPRequestOperationManager based on NSURLConnection
• OVCHTTPSessionManager based on NSURLSession

Both classes have identical APIs, but developers targeting OS X 10.9+ or iOS 7.0+ are encouraged to subclass OVCHTTPSessionManager. Developers targeting OS X 10.8 or iOS 6.0 must subclass OVCHTTPRequestOperationManager.

#import <Overcoat/Overcoat.h>

@interface TwitterClient : OVCHTTPSessionManager
...
@end

To specify how responses should be mapped to model classes you must override +modelClassesByResourcePath and return a dictionary mapping resource paths to model classes.

+ (NSDictionary *)modelClassesByResourcePath {
    return @{
               @"statuses/*": [Tweet class],
               @"users/*": [TwitterUser class],
               @"friends/ids.json": [UserIdentifierCollection class],
               @"followers/ids.json": [UserIdentifierCollection class]
    };
}

You don't need to specify the full path, and you can use * to match any text or # to match only digits. However, path matching is strict and the number of path components must be equal.

Different REST APIs have different ways of dealing with status and other metadata.

Pure REST services like Twitter use HTTP status codes and a specific JSON response to communicate errors; and HTTP headers for other metadata like rate limits. For these kind of services, you may want to override +errorModelClass to map error responses into your own model.

+ (Class)errorModelClass {
    return [TwitterErrorResponse class];
}

Other services like App.net use an envelop response, which is a top level JSON response containing the data requested and additional metadata. For these kind of services, you must create your own OVCResponse subclass and specify the data key path.

@interface AppDotNetResponse : OVCResponse
...
@end

@implementation AppDotNetResponse
+ (NSString *)resultKeyPathForJSONDictionary:(NSDictionary *)JSONDictionary {
    return @"data";
}
@end

You can then specify which response class to use in your client by overriding +responseClass.

+ (Class)responseClass {
    return [AppDotNetResponse class];
}

If you initialize your client with a valid NSManagedObjectContext, it will automatically persist any model object(s) parsed from a response, if the model supports Core Data serialization (that is, implements MTLManagedObjectSerializing).

Note that, if you provide a context with an NSMainQueueConcurrencyType, a private context will be created to perform insertions in the background.

You can see Core Data Serialization in action in the provided example.

Both OVCHTTPRequestOperationManager and OVCHTTPSessionManager provide the same methods for making HTTP requests.

// Lookup Twitter users
NSDictionary *parameters = @{
    @"screen_name": @"gonzalezreal",
    @"user_id": @"42,3141592"
};

[twitterClient GET:@"users/lookup.json" parameters:parameters completion:^(OVCResponse *response, NSError *error) {
    NSArray *users = response.result; // This is an array of TwitterUser objects!
}];

Note that Overcoat automatically parses the JSON into model objects, that is, in this case response.result contains an array of TwitterUser objects.

Overcoat 2.0 adds support for ReactiveCocoa.

Add the following to your Podfile to install Overcoat with ReactiveCocoa support:

pod 'Overcoat/ReactiveCocoa', '~>2.0'

Now you can make HTTP requests and get cold signals to handle responses:

#import <Overcoat/ReactiveCocoa+Overcoat.h>
...
[[twitterClient rac_GET:@"users/lookup.json" parameters:parameters] subscribeNext:^(OVCResponse *response) {
    ...
} error:^(NSError *e) {
    ...
}];

If you're looking for a better way to handle asynchronous calls but you're not ready to embrace ReactiveCocoa, you may try PromiseKit.

Add the following to your Podfile to install Overcoat with PromiseKit support:

pod 'Overcoat/PromiseKit', '~>2.0'

Now you can get PMKPromise objects when making HTTP requests:

#import <Overcoat/PromiseKit+Overcoat.h>
...
[twitterClient GET:@"users/lookup.json" parameters:parameters].then(^(OVCResponse *response) {
    return response.result;
});

In order to build the library and run unit tests, you will first need to install project dependencies by running $ pod install in the project directory.

Once the process is complete open the generated Overcoat.xcworkspace with Xcode.

Guillermo Gonzalez
@gonzalezreal

Overcoat is available under the MIT license. See LICENSE.md.