Allow DataParser to return typed objects

DataParser should not be required to return Any and have objects checked for type safety at runtime. This allows us to use the Swift build time type checking system with very minimal changes to existing code. The only API breaking change is that Request classes using the default JSONDataParser should now conform to JSONRequest, instead of just Request. This is because protocol extensions cannot declare default associated types.

Author: gormster

Sources/APIKit/DataParser/DataParser.swift

@@ -2,10 +2,12 @@ import Foundation
 
 /// `DataParser` protocol provides inteface to parse HTTP response body and to state Content-Type to accept.
 public protocol DataParser {
+    associatedtype Parsed
+
     /// Value for `Accept` header field of HTTP request.
     var contentType: String? { get }
 
     /// Return `Any` that expresses structure of response such as JSON and XML.
     /// - Throws: `Error` when parser encountered invalid format data.
-    func parse(data: Data) throws -> Any
+    func parse(data: Data) throws -> Parsed
 }

Sources/APIKit/Request.swift

@@ -11,6 +11,7 @@ import Result
 public protocol Request {
     /// The response type associated with the request type.
     associatedtype Response
+    associatedtype Parser: DataParser
 
     /// The base URL.
     var baseURL: URL { get }
@@ -41,7 +42,7 @@ public protocol Request {
     var headerFields: [String: String] { get }
 
     /// The parser object that states `Content-Type` to accept and parses response body.
-    var dataParser: DataParser { get }
+    var dataParser: Parser { get }
 
     /// Intercepts `URLRequest` which is created by `Request.buildURLRequest()`. If an error is
     /// thrown in this method, the result of `Session.send()` turns `.failure(.requestError(error))`.
@@ -53,15 +54,16 @@ public protocol Request {
     /// The default implementation of this method is provided to throw `RequestError.unacceptableStatusCode`
     /// if the HTTP status code is not in `200..<300`.
     /// - Throws: `Error`
-    func intercept(object: Any, urlResponse: HTTPURLResponse) throws -> Any
+    func intercept(object: Parser.Parsed, urlResponse: HTTPURLResponse) throws -> Parser.Parsed
 
     /// Build `Response` instance from raw response object. This method is called after
     /// `intercept(object:urlResponse:)` if it does not throw any error.
     /// - Throws: `Error`
-    func response(from object: Any, urlResponse: HTTPURLResponse) throws -> Response
+    func response(from object: Parser.Parsed, urlResponse: HTTPURLResponse) throws -> Response
 }
 
 public extension Request {
+
     public var parameters: Any? {
         return nil
     }
@@ -86,15 +88,11 @@ public extension Request {
         return [:]
     }
 
-    public var dataParser: DataParser {
-        return JSONDataParser(readingOptions: [])
-    }
-
     public func intercept(urlRequest: URLRequest) throws -> URLRequest {
         return urlRequest
     }
 
-    public func intercept(object: Any, urlResponse: HTTPURLResponse) throws -> Any {
+    public func intercept(object: Parser.Parsed, urlResponse: HTTPURLResponse) throws -> Parser.Parsed {
         guard 200..<300 ~= urlResponse.statusCode else {
             throw ResponseError.unacceptableStatusCode(urlResponse.statusCode)
         }
@@ -146,3 +144,13 @@ public extension Request {
         return try response(from: passedObject, urlResponse: urlResponse)
     }
 }
+
+public protocol JSONRequest: Request {}
+
+public extension JSONRequest {
+
+    public var dataParser: JSONDataParser {
+        return JSONDataParser(readingOptions: [])
+    }
+
+}

Tests/APIKitTests/SessionTests.swift

@@ -175,7 +175,7 @@ class SessionTests: XCTestCase {
         waitForExpectations(timeout: 1.0, handler: nil)
     }
 
-    struct AnotherTestRequest: Request {
+    struct AnotherTestRequest: JSONRequest {
         typealias Response = Void
 
         var baseURL: URL {

Tests/APIKitTests/TestComponents/TestRequest.swift

@@ -1,7 +1,7 @@
 import Foundation
 import APIKit
 
-struct TestRequest: Request {
+struct TestRequest: JSONRequest {
     var absoluteURL: URL? {
         let urlRequest = try? buildURLRequest()
         return urlRequest?.url