Endpoints makes it easy to write a type-safe network abstraction layer for any Web-API.
It requires Swift 3, makes heavy use of generics (and generalized existentials) and protocols (and protocol extensions). It also encourages a clean separation of concerns and the use of value types (i.e. structs).
Here's how to load a random image from Giphy.
// A client is responsible for encoding and parsing all calls for a given Web-API.
let client = AnyClient(baseURL: URL(string: "https://api.giphy.com/v1/")!)
// A call encapsulates the request that is sent to the server and the type that is expected in the response.
let call = AnyCall<Data>(Request(.get, "gifs/random", query: [ "tag": "cat", "api_key": "dc6zaTOxFJmzC" ]))
// A session wraps `URLSession` and allows you to start the request for the call and get the parsed response object (or an error) in a completion block.
let session = Session(with: client)
// enable debug-mode to log network traffic
session.debug = true
// start call
session.start(call: call) { result in
result.onSuccess { value in
//value is an object of the type specified in `Call`
}.onError { error in
//something went wrong
}
}A call is supposed to know exactly what response to expect from its request. It delegates the parsing of the response to a ResponseParser.
Some built-in types already adopt the ResponseParser protocol (using protocol extensions), so you can for example turn any response into a JSON array or dictionary:
// Replace `Data` with any `ResponseParser` implementation
let call = AnyCall<[String: Any]>(Request(.get, "gifs/random", query: [ "tag": "cat", "api_key": "dc6zaTOxFJmzC" ]))
...
session.start(call: call) { result in
result.onSuccess { value in
//value is now a JSON dictionary 🎉
}
}AnyCall is the default implementation of the Call protocol, which you can use as-is. But if you want to make your networking layer really type-safe you'll want to create a dedicated Call type for each operation of your Web-API:
struct GetRandomImage: Call {
typealias ResponseType = [String: Any]
var tag: String
var request: URLRequestEncodable {
return Request(.get, "gifs/random", query: [ "tag": tag, "api_key": "dc6zaTOxFJmzC" ])
}
}
// `GetRandomImage` is much safer and easier to use than `AnyCall`
let call = GetRandomImage(tag: "cat")A client is responsible for handling things that are common for all operations of a given Web-API. Typically this includes appending API tokens or authentication tokens to a request or validating responses and handling errors.
AnyClient is the default implementation of the Client protocol and can be used as-is or as a starting point for your own dedicated client.
You'll usually need to create your own dedicated client that either subclasses AnyClient or delegates the encoding of requests and parsing of responses to an AnyClient instance, as done here:
class GiphyClient: Client {
private let anyClient = AnyClient(baseURL: URL(string: "https://api.giphy.com/v1/")!)
var apiKey = "dc6zaTOxFJmzC"
func encode<C: Call>(call: C) -> URLRequest {
var request = anyClient.encode(call: call)
// Append the API key to every request
request.append(query: ["api_key": apiKey])
return request
}
public func parse<C : Call>(sessionTaskResult result: URLSessionTaskResult, for call: C) throws -> C.ResponseType.OutputType {
do {
// Use `AnyClient` to parse the response
// If this fails, try to read error details from response body
return try anyClient.parse(sessionTaskResult: result, for: call)
} catch {
// See if the backend sent detailed error information
guard
let response = result.httpResponse,
let data = result.data,
let errorDict = try? JSONSerialization.jsonObject(with: data, options: .allowFragments) as? [String: Any],
let meta = errorDict?["meta"] as? [String: Any],
let errorCode = meta["error_code"] as? String else {
// no error info from backend -> rethrow default error
throw error
}
// Propagate error that contains errorCode as reason from backend
throw StatusCodeError.unacceptable(code: response.statusCode, reason: errorCode)
}
}
}You usually want your networking layer to provide a dedicated response type for every supported call. In our example this could look like this:
struct RandomImage {
var url: URL
...
}
struct GetRandomImage: Call {
typealias ResponseType = RandomImage
...
}In order for this to work, RandomImage must adopt the ResponseParser protocol:
extension RandomImage: ResponseParser {
static func parse(data: Data, encoding: String.Encoding) throws -> RandomImage {
let dict = try [String: Any].parse(data: data, encoding: encoding)
guard let data = dict["data"] as? [String : Any], let url = data["image_url"] as? String else {
throw throw ParsingError.invalidData(description: "invalid response. url not found")
}
return RandomImage(url: URL(string: url)!)
}
}This can of course be made a lot easier by using a JSON parsing library (like Unbox) and a few lines of integration code:
protocol UnboxableParser: Unboxable, ResponseParser {}
extension UnboxableParser {
static func parse(data: Data, encoding: String.Encoding) throws -> Self {
return try unbox(data: data)
}
}Now we can write:
struct RandomImage: UnboxableParser {
var url: URL
init(unboxer: Unboxer) throws {
url = try unboxer.unbox(keyPath: "data.image_url")
}
}With all the parts in place, users of your networking layer can now perform type-safe requests and get a type-safe response with a few lines of code:
let client = GiphyClient()
let call = GetRandomImage(tag: "cat")
let session = Session(with: client)
session.start(call: call) { result in
result.onSuccess { value in
print("image url: \(value.url)")
}.onError { error in
print("error: \(error)")
}
}There are multiple ways to make performing a call more convenient. You could write a dedicated GiphyCall that creates the correct Client and Session for your users:
protocol GiphyCall: Call {}
extension GiphyCall {
func start(completion: @escaping (Result<ResponseType.OutputType>)->()) {
let client = GiphyClient()
let session = Session(with: client)
session.start(call: self, completion: completion)
}
}When GiphyCall is adopted by GetRandomImage instead of Call, performing a request is much simpler:
GetRandomImage(tag: "cat").start { result in ... }To make it easer to find supported calls, you could namespace your calls using an extension of your Client:
extension GiphyClient {
struct GetRandomImage: GiphyCall { ... }
}Xcode can now help developers find the right Call instance:
GiphyClient.GetRandomImage(tag: "cat").start { result in ... }CocoaPods:
pod "Endpoints"
Carthage:
github "tailoredmedia/Endpoints.git"
Swift Package Manager:
.Package(url: "https://github.com/tailoredmedia/Endpoints.git", majorVersion: 0)
To compile examples you need to download some dependencies using the Swift Package Manager.
Just open Terminal at Endpoints/Example/Core and type swift package fetch.
- Swift 3
- iOS 8
- tvOS 9
- macOS 10.11
- watchOS 2.0
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