Custom decoder for RestClient

Split/Api/SplitClientManager.swift

@@ -101,7 +101,7 @@ class DefaultClientManager: SplitClientManager {
                 return
             }
             Logger.v("Cache validated; starting sync manager")
-            syncManager.start()
+            self.syncManager.start()
         }
     }
 

Split/Network/DataParsing/Json.swift

@@ -38,6 +38,18 @@ struct Json {
         return try Self.decodeFrom(json: data, to: type)
     }
 
+    /// Decode using a custom decoder function
+    /// - Parameters:
+    ///   - decoder: A function that takes Data and returns a decoded object of type T
+    /// - Returns: The decoded object
+    /// - Throws: Decoding errors if the JSON cannot be parsed
+    func decodeWith<T>(_ decoder: (Data) throws -> T) throws -> T? {
+        guard let data = data else {
+            return nil
+        }
+        return try decoder(data)
+    }
+
     func dynamicDecode<T>(_ type: T.Type) throws -> T? where T: DynamicDecodable {
         var obj: T?
         if let data = self.data {

Split/Network/RestClient/RestClient.swift

@@ -56,6 +56,7 @@ class DefaultRestClient: SplitApiRestClient {
                     parameters: HttpParameters? = nil,
                     body: Data? = nil,
                     headers: HttpHeaders? = nil,
+                    customDecoder: ((Data) throws -> T)? = nil,
                     completion: @escaping (DataResult<T>) -> Void) where T: Decodable {
 
         do {
@@ -73,8 +74,18 @@ class DefaultRestClient: SplitApiRestClient {
                 }
 
                 do {
-                    let parsedObject = try json.decode(T.self)
-                    completion(DataResult { return parsedObject })
+                    if let customDecoder = customDecoder {
+                        // Use the custom decoder if provided
+                        if let parsedObject = try json.decodeWith(customDecoder) {
+                            completion(DataResult { return parsedObject })
+                        } else {
+                            completion(DataResult { return nil })
+                        }
+                    } else {
+                        // Use the default decoder
+                        let parsedObject = try json.decode(T.self)
+                        completion(DataResult { return parsedObject })
+                    }
                 } catch {
                     completion(DataResult { throw error })
                 }

SplitTests/RestClientCustomDecoderTest.swift

@@ -0,0 +1,137 @@
+//
+//  RestClientCustomDecoderTest.swift
+//  SplitTests
+//
+//  Created on 13/05/2025.
+//  Copyright © 2025 Split. All rights reserved.
+//
+
+import XCTest
+@testable import Split
+
+class RestClientCustomDecoderTest: XCTestCase {
+
+    private var httpSession: HttpSessionMock!
+    private var requestManager: HttpRequestManagerMock!
+    private var restClient: DefaultRestClient!
+
+    override func setUp() {
+        super.setUp()
+        httpSession = HttpSessionMock()
+        requestManager = HttpRequestManagerMock()
+        let serviceEndpoints = ServiceEndpoints.builder()
+            .set(sdkEndpoint: "https://sdk.split-test.io")
+            .set(eventsEndpoint: "https://events.split-test.io").build()
+        let endpointFactory = EndpointFactory(serviceEndpoints: serviceEndpoints, apiKey: "dummy-key", splitsQueryString: "")
+        let httpClient = DefaultHttpClient(session: httpSession, requestManager: requestManager)
+        restClient = DefaultRestClient(httpClient: httpClient, endpointFactory: endpointFactory)
+    }
+
+    override func tearDown() {
+        httpSession = nil
+        requestManager = nil
+        restClient = nil
+        super.tearDown()
+    }
+
+    func testExecuteWithDefaultDecoder() {
+        let json = """
+        {
+            "id": 123,
+            "name": "test"
+        }
+        """
+
+        let dummyData = Data(json.utf8)
+        let expectation = XCTestExpectation(description: "API call completes")
+        var result: TestModel?
+        var error: Error?
+
+        restClient.execute(
+            endpoint: restClient.endpointFactory.splitChangesEndpoint,
+            parameters: nil,
+            headers: nil,
+            completion: { (dataResult: DataResult<TestModel>) in
+                do {
+                    result = try dataResult.unwrap()
+                    expectation.fulfill()
+                } catch let err {
+                    error = err
+                    expectation.fulfill()
+                }
+            })
+
+        requestManager.append(data: dummyData, to: 1)
+        _ = requestManager.set(responseCode: 200, to: 1)
+
+        wait(for: [expectation], timeout: 1)
+
+        XCTAssertEqual(1, httpSession.dataTaskCallCount)
+        XCTAssertEqual(1, requestManager.addRequestCallCount)
+        XCTAssertNil(error)
+        XCTAssertNotNil(result)
+        XCTAssertEqual(result?.id, 123)
+        XCTAssertEqual(result?.name, "test")
+    }
+
+    func testExecuteWithCustomDecoder() {
+        let json = """
+        {
+            "custom_id": 456,
+            "custom_name": "custom_test"
+        }
+        """
+
+        let dummyData = Data(json.utf8)
+        let expectation = XCTestExpectation(description: "API call completes")
+        let customDecoderCalled = XCTestExpectation(description: "Custom decoder called")
+        var result: TestModel?
+        var error: Error?
+
+        let customDecoder: (Data) throws -> TestModel = { data in
+            customDecoderCalled.fulfill()
+
+            let decoder = JSONDecoder()
+            let customModel = try decoder.decode(CustomTestModel.self, from: data)
+            // Convert from custom model to standard model
+            return TestModel(id: customModel.custom_id, name: customModel.custom_name)
+        }
+
+        restClient.execute(
+            endpoint: restClient.endpointFactory.splitChangesEndpoint,
+            parameters: nil,
+            headers: nil,
+            customDecoder: customDecoder,
+            completion: { (dataResult: DataResult<TestModel>) in
+                do {
+                    result = try dataResult.unwrap()
+                    expectation.fulfill()
+                } catch let err {
+                    error = err
+                    expectation.fulfill()
+                }
+            })
+
+        requestManager.append(data: dummyData, to: 1)
+        _ = requestManager.set(responseCode: 200, to: 1)
+
+        wait(for: [expectation, customDecoderCalled], timeout: 1)
+
+        XCTAssertEqual(1, httpSession.dataTaskCallCount)
+        XCTAssertEqual(1, requestManager.addRequestCallCount)
+        XCTAssertNil(error)
+        XCTAssertNotNil(result)
+        XCTAssertEqual(result?.id, 456)
+        XCTAssertEqual(result?.name, "custom_test")
+    }
+}
+
+private struct TestModel: Decodable {
+    let id: Int
+    let name: String
+}
+
+private struct CustomTestModel: Decodable {
+    let custom_id: Int
+    let custom_name: String
+}