Async HTTP API shoppers in Swift

Introducing SwiftHttp

An superior Swift HTTP library to quickly create communication layers with API endpoints. The library tries to separate the consumer request logic from the request constructing and response dealing with. That is the primary cause why it has a HttpClient protocol which can be utilized to carry out information, obtain and add duties. You possibly can implement your personal HttpClient, however SwiftHttp comes with a built-in UrlSessionHttpClient based mostly on Basis networking.

So the consumer is chargeable for executing the requests, however we nonetheless have to explain the request itself by some means. That is the place the HttpRawRequest object comes into play. You possibly can simply create a base HttpUrl and carry out a request utilizing the HttpRawRequest object. When working with a uncooked request you possibly can specify further header fields and a uncooked physique information object too. 💪

let url = HttpUrl(scheme: "https",
                  host: "jsonplaceholder.typicode.com",
                  port: 80,
                  path: ["todos"],
                  useful resource: nil,
                  question: [:],
                  fragment: nil)

let req = HttpRawRequest(url: url, technique: .get, headers: [:], physique: nil)


let consumer = UrlSessionHttpClient(session: .shared, log: true)
let response = attempt await consumer.dataTask(req)


let todos = attempt JSONDecoder().decode([Todo].self, from: response.information)

The HTTP consumer can carry out community calls utilizing the brand new async / await Swift concurrency API. It’s potential to cancel a community request by wrapping it right into a structured concurrency Job.

let job = Job {
    let api = TodoApi()
    _ = attempt await api.checklist()
}

DispatchQueue.international().asyncAfter(deadline: .now() + .milliseconds(10)) {
    job.cancel()
}

do {
    let _ = attempt await job.worth
}
catch {
    if (error as? URLError)?.code == .cancelled {
        print("cancelled")
    }
}

It is a neat tick, you can too test the explanation contained in the catch block, whether it is an URLError with a .cancelled code then the request was cancelled, in any other case it should be some kind of community error.

So that is how you need to use the consumer to carry out or cancel a community job, however often you do not need to work with uncooked information, however encodable and decodable objects. Once you work with such objects, you may need to validate the response headers and ship further headers to tell the server about the kind of the physique information. Simply take into consideration the Content material-Kind / Settle for header fields. 🤔

So we’d need to ship further headers alongside the request, plus it would be good to validate the standing code and response headers earlier than we attempt to parse the info. This looks like a movement of widespread operations, first we encode the info, set the extra header fields, and when the response arrives we validate the standing code and the header fields, lastly we attempt to decode the info object. It is a typical use case and SwiftHttp calls this workflow as a pipeline.

There are 4 kinds of built-in HTTP pipelines:

• Uncooked – Ship a uncooked information request, return a uncooked information response
• Encodable – Ship an encodable object, return a uncooked information response
• Decodable – Ship a uncooked information request, return a decodable object
• Codable – Ship an encodable object, return a decodable object

We are able to use a HttpRawPipeline and execute our request utilizing a consumer as an executor.

let baseUrl = HttpUrl(host: "jsonplaceholder.typicode.com")
let consumer = UrlSessionHttpClient(session: .shared, log: true)

let pipeline = HttpRawPipeline(url: baseUrl.path("todos"), technique: .get)

let response = attempt await pipeline.execute(consumer.dataTask)
let todos = attempt JSONDecoder().decode([Todo].self, from: response.information)
print(response.statusCode)
print(todos.rely)

On this case we have been utilizing the dataTask perform, however if you happen to anticipate the response to be an enormous file, you may need to think about using a downloadTask, or if you happen to’re importing a considerable amount of information when sending the request, you need to select the uploadTask perform. 💡

So on this case we needed to manually decode the Todo object from the uncooked HTTP response information, however we are able to use the decodable pipeline to make issues much more easy.

let baseUrl = HttpUrl(host: "jsonplaceholder.typicode.com")
let consumer = UrlSessionHttpClient(session: .shared, log: true)


let pipeline = HttpDecodablePipeline<[Todo]>(url: baseUrl.path("todos"),
                                             technique: .get,
                                             decoder: .json(JSONDecoder(), validators: [
                                                HttpStatusCodeValidator(.ok),
                                                HttpHeaderValidator(.key(.contentType)) {
                                                    $0.contains("application/json")
                                                },
                                             ]))

let todos = attempt await pipeline.execute(consumer.dataTask)
print(todos.rely)

As you possibly can see, on this case the as a substitute of returning the response, the pipeline can carry out further validation and the decoding utilizing the supplied decoder and validators. You possibly can create your personal validators, there’s a HttpResponseValidator protocol for this goal.

The encodable pipeline works like the identical, you possibly can specify the encoder, you possibly can present the encodable object and you will get again a HttpResponse occasion.

let consumer = UrlSessionHttpClient(session: .shared, log: true)
        
let todo = Todo(id: 1, title: "lorem ipsum", accomplished: false)

let pipeline = HttpEncodablePipeline(url: baseUrl.path("todos"),
                                     technique: .publish,
                                     physique: todo,
                                     encoder: .json())

let response = attempt await pipeline.execute(consumer.dataTask)

print(response.statusCode == .created)

The codable pipeline is a mixture of the encodable and decodable pipeline. 🙃

let baseUrl = HttpUrl(host: "jsonplaceholder.typicode.com")
let consumer = UrlSessionHttpClient(session: .shared, log: true)

let todo = Todo(id: 1, title: "lorem ipsum", accomplished: false)

let pipeline = HttpCodablePipeline<Todo, Todo>(url: baseUrl.path("todos", String(1)),
                                               technique: .put,
                                               physique: todo,
                                               encoder: .json(),
                                               decoder: .json())

let todo = attempt await pipeline.execute(consumer.dataTask)
print(todo.title)

As you possibly can see that is fairly a typical sample, and once we’re speaking with a REST API, we will carry out roughly the very same community calls for each single endpoint. SwiftHttp has a pipeline assortment protocol that you need to use to carry out requests with out the necessity of explicitly establishing these pipelines. Here is an instance:

import SwiftHttp

struct Todo: Codable {
    let id: Int
    let title: String
    let accomplished: Bool
}

struct TodoApi: HttpCodablePipelineCollection {

    let consumer: HttpClient = UrlSessionHttpClient(log: true)
    let apiBaseUrl = HttpUrl(host: "jsonplaceholder.typicode.com")

    
    func checklist() async throws -> [Todo] {
        attempt await decodableRequest(executor: consumer.dataTask,
                                   url: apiBaseUrl.path("todos"),
                                   technique: .get)
    }    
}

let todos = attempt await api.checklist()

When utilizing a HttpCodablePipelineCollection you possibly can carry out an encodable, decodable or codable request utilizing an executor object. It will scale back the boilerplate code wanted to carry out a request and every part goes to be kind protected because of the generic protocol oriented networking layer. You possibly can setup as many pipeline collections as you want, it’s potential to make use of a shared consumer or you possibly can create a devoted consumer for every.

By the way in which, if one thing goes mistaken with the request, or one of many validators fail, you possibly can at all times test for the errors utilizing a do-try-catch block. 😅

do {
    _ = attempt await api.checklist()
}
catch HttpError.invalidStatusCode(let res) {
    
    let decoder = HttpResponseDecoder<CustomError>(decoder: JSONDecoder())
    do {
        let error = attempt decoder.decode(res.information)
        print(res.statusCode, error)
    }
    catch {
        print(error.localizedDescription)
    }
}
catch {
    print(error.localizedDescription)
}

That is how SwiftHttp works in a nutshell, in fact you possibly can setup customized encoders and decoders, however that is one other matter. If you’re within the mission, be happy to present it a star on GitHub. We’ll use it sooner or later rather a lot each on the consumer and server aspect. ⭐️⭐️⭐️