Hello!

Siddharth Gupta

@sids7

iOS at Flipkart

Agenda

Why Another Networking Library?
State of the Art
WebService - How does it help?
Swifty - How does it help?
Performance Benchmarks

"Why another networking library?"

Modern Apps have complex

networking requirements

Capabilities

Request Conditions: OAuth Token? Location Access?
Session Systems: Attaching headers to every request
Adaptive to network connectivity

Where to keep my networking code?

The Networking Subsystem
Some kind of abstraction over popular libraries like Alamofire / Siesta
Requests can be scattered in view/controller/store layers
Helpers / Singletons can be used to share common request creation code

Let's Look at Artsy

State of the Art:

Moya

Can we do

better?

What do we need?

Organised

One place for all your requests

Concise

Simple & Familiar

Readable

Easy to Understand

WebService

simple, readable, declarative way of writing network requests

all request creation code in one place

your API becomes a type

your requests become functions

Demo




class Bin: WebService {
    
    static var serverURL = "https://httpbin.org"
    
    static var networkInterface: WebServiceNetworkInterface = Swifty()
    
    static func getIP() -> NetworkResource {
        return server.get("ip")
    }
    
    static func createUser(user: [String: String]) -> NetworkResource {
        return server.post("post").json(body: user).header(key: "My", value: "Header")
    }

}

This is your API ( a type)

This is a request (a function)

Usage

in Objective-C


@implementation ViewController: UIViewController {

- (void) viewDidLoad {
        
    

}

@end

in Objective-C


@implementation ViewController: UIViewController {

- (void) viewDidLoad {
        
    [Bin getIP]

}

@end

in Objective-C


@implementation ViewController: UIViewController {

- (void) viewDidLoad {
        
    [Bin getIP] load:^{
        
    }];

}

@end

in Objective-C


@implementation ViewController: UIViewController {

- (void) viewDidLoad {
        
    [Bin getIP] load:^(NSURLResponse *response, id data, NSError *error){
        // Here's your response
    }];

}

@end




static func getIP() -> NetworkResource {
    return server.get("ip")
}




static func getIP() -> NetworkResource {
    return server.get("ip")
                 .json("user": "name")
}




static func getIP() -> NetworkResource {
    return server.get("ip")
                 .query("user": "name")
}

Compile Time Checks

server

.get()

.post()

.put()

.delete()

.query()

.fields()

.data()

.json()

.header()

.contentType()

.priority()

.mock()

.deliver(on:)

.tag()

.deliver(on:)


class ViewController: UIViewController {

    override viewDidLoad(){
        
        Bin.getIP().load(){ (response, data, error) in
            // Here's your response
        }

    }

}


class DataStore {

    // Should work in the background
    override refreshIP(){
        
  
    
    }
}

.deliver(on:)


class DataStore {

    // Should work in the background
    override refreshIP(){
        
        let backgroundQueue = DispatchQueue("com.background.processing")

       
    
    }
}

.deliver(on:)


class DataStore {

    // Should work in the background
    override refreshData(){
        
        let backgroundQueue = DispatchQueue("com.background.processing")

        Bin.getIP()
    
    }
}

.deliver(on:)


class DataStore {

    // Should work in the background
    override refreshData(){
        
        let backgroundQueue = DispatchQueue("com.background.processing")

        Bin.getIP().deliver(on: backgroundQueue)
    
    }
}

.deliver(on:)


class DataStore {

    // Should work in the background
    override refreshData(){
        
        let backgroundQueue = DispatchQueue("com.background.processing")

        Bin.getIP().deliver(on: backgroundQueue).load(){ ... }
    
    }
}

.priority()




class Bin: WebService {
    
    static var serverURL = "https://httpbin.org"
    
    static var networkInterface: WebServiceNetworkInterface = Swifty()
    
    static func getIP() -> NetworkResource {
        return server.get("ip")
    }
    
    static func createUser(user: [String: String]) -> NetworkResource {
        return server.post("post").json(body: user)
    }

}

.priority()




class Bin: WebService {
    
    static var serverURL = "https://httpbin.org"
    
    static var networkInterface: WebServiceNetworkInterface = Swifty()
    
    static func getIP() -> NetworkResource {
        return server.get("ip").priority(.high)
    }
    
    static func createUser(user: [String: String]) -> NetworkResource {
        return server.post("post").json(body: user)
    }

}

.mock()




static func getIP() -> NetworkResource {
        return server.get("ip")
}

.mock()




static func getIP() -> NetworkResource {
        return server.get("ip").mock
}

.mock()




static func getIP() -> NetworkResource {
        return server.get("ip").mock(file: "response.json")
}

server

.get()

.post()

.put()

.delete()

.query()

.fields()

.data()

.json()

.header()

.contentType()

.priority()

.mock()

.deliver(on:)

.tag()

Extending WebService


extension NetworkResource {

    


}

Encrypt Data and Set Body

Extending WebService


extension NetworkResource {

    func encrypt(data: Data){
        
    }


}

Encrypt Data and Set Body

Extending WebService


extension NetworkResource {

    func encrypt(data: Data) -> NetworkResource {
        
    }


}

Encrypt Data and Set Body

Extending WebService


extension NetworkResource {

    func encrypt(data: Data) -> NetworkResource {
        let encrptedData = ourSecretEncryptor(data)
    }


}

Encrypt Data and Set Body

Extending WebService


extension NetworkResource {

    func encrypt(data: Data) -> NetworkResource {
        let encrptedData = ourSecretEncryptor(data)
        self.data(encryptedData)
    }


}

Encrypt Data and Set Body

Extending WebService


extension NetworkResource {

    func encrypt(data: Data) -> NetworkResource {
        let encrptedData = ourSecretEncryptor(data)
        self.data(encryptedData)
        return self
    }


}

Encrypt Data and Set Body

server

.get()

.post()

.put()

.delete()

.query()

.fields()

.data()

.json()

.header()

.contentType()

.encrypt()

.priority()

.mock()

.deliver(on:)

.tag()

WebService abstracts the actual networking from the upper layers

Gives you a simple async syntax: .load()

Multiple WebServices in your app is completely Acceptable

Example: one for contacting your server, one for external servers

You still have granular control over the networking

the module that powers your .load() function

Swifty

Based on NSURLSession
Works using GCD APIs like DispatchGroup & Serial DispatchQueue Mutexes
Initializer only needs an NSURLSessionConfiguration
Deep integration with URLSessionTaskMetrics API

Constraints

Classes which determine a network request has everything it needs to succeed.
If not, the class can try to satisfy the constraint
Classic Example: OAuth Token Constraint

Constraints

Another use case: Requiring system permissions before you perform actions
- Location access required to perform a request
Constraints provide asynchronous APIs: No hurry/blocking threads to satisfy constraints, the requests will wait.

Constraints


class OAuthConstraint: Constraint {

  override func isConstraintSatisfied(for resource: NetworkResource) -> Bool {
	// return false if we don't have the OAuth Token
	// return true if we already have the OAuth Token
  }

  override func satisfyConstraint(for resource: NetworkResource) {
	// Get the OAuth token from the server
	// Make sure to call finish() when done
	finish()
  }
}

Interceptors

Request Interceptors: Run before each request is fired over the network
Response Interceptors: Run right after each response is received, and before it is returned to the caller

Request Interceptors

A great time to attach authentication/important headers into your requests

Request Interceptors


class OAuthTokenAddingInterceptor: RequestInterceptor {

	func intercept(resource: NetworkResource) -> NetworkResource {
		
		// Get the token from where your Constraint 
		let token = Keychain.string(key: "OAuth")
		
		// Attach it to the resource:
		resource.header(key: "Token", value: token)
		
		// Return the modified resource
		return resource
	}

}

Response Interceptors

A great time to extract information in responses for system use (eg. session)
Other use cases:
- Collecting/Logging Statistics on Request Failure Rates / URLSessionTaskMetrics
- Modify Faulty Responses / Errors Sent by Server

Response Interceptors


class ErrorCheckingInterceptor: ResponseInterceptor {

	func intercept(response: NetworkResponse) -> NetworkResponse {
		
		if let statusCode = response.response?.statusCode, statusCode == 204 {
			response.fail(error: SwiftyError.responseValidation())
		}
		
		return response
	}

}

The Best of Both Worlds

The Constraint + Request Interceptor Combo
Best Example: OAuth Logic
- Get an OAuth Token from server if not already present (Constraint)
- Attach it to every request that goes through (Request Interceptor)

Swifty or Alamofire

Alamofire is great if you want to quick access to networking. Simple syntax, fast access to network. Hence the singleton access.
Swifty is something you make your own. You customize it according to your own needs.
Multiple Instances per app with different configurations.

Performance Benchmarks

Performance Tests in the Example Project

Limitations

Request RetriesCancellation
HTTP Digest Authentication
SSL Certificate Pinning

Roadmap

Request Retries .retry()
HTTP Digest Authentication
- .authentication() .digestAuthentication()

Roadmap

Request Retries .retry()
HTTP Digest Authentication
- .authentication() .digestAuthentication()
- Expose More URLSession: SSL Certificate Pinning
Type Safe Response Adapters

The Swifty Inspector

~ 8000 downloads ⏬

58 apps 🚀

Swifty

Open Source

https://github.com/Flipkart/Swifty

pod try Swifty or pod 'Swifty'