如何解码Alamofire 5中的错误主体

Question

我正试图将我的项目从Alamofire 4.9迁移到5.3，但我在错误处理方面遇到了困难。我想尽可能多地使用Decodable，但当一切顺利时，我的API端点返回一个JSON结构，当出现错误时返回一个不同的JSON结构，所有端点上的所有错误都是一样的。我的代码中对应的Codable是ApiError。

我想创建一个自定义响应序列化程序，它可以给我一个Result<T, ApiError>，而不是默认的Result<T, AFError>。我发现这篇文章似乎解释了一般过程，但其中的代码并没有编译。

如何创建这样一个自定义ResponseSerializer？

Answer 1

我最终使用了以下ResponseSerializer:

struct APIError: Error, Decodable {
    let message: String
    let code: String
    let args: [String]
}
final class TwoDecodableResponseSerializer<T: Decodable>: ResponseSerializer {
    
    lazy var decoder: JSONDecoder = {
        let decoder = JSONDecoder()
        decoder.dateDecodingStrategy = .iso8601
        return decoder
    }()
    private lazy var successSerializer = DecodableResponseSerializer<T>(decoder: decoder)
    private lazy var errorSerializer = DecodableResponseSerializer<APIError>(decoder: decoder)
    public func serialize(request: URLRequest?, response: HTTPURLResponse?, data: Data?, error: Error?) throws -> Result<T, APIError> {
        guard error == nil else { return .failure(APIError(message: "Unknown error", code: "unknown", args: [])) }
        guard let response = response else { return .failure(APIError(message: "Empty response", code: "empty_response", args: [])) }
        do {
            if response.statusCode < 200 || response.statusCode >= 300 {
                let result = try errorSerializer.serialize(request: request, response: response, data: data, error: nil)
                return .failure(result)
            } else {
                let result = try successSerializer.serialize(request: request, response: response, data: data, error: nil)
                return .success(result)
            }
        } catch(let err) {
            return .failure(APIError(message: "Could not serialize body", code: "unserializable_body", args: [String(data: data!, encoding: .utf8)!, err.localizedDescription]))
        }
    }
}
extension DataRequest {
    @discardableResult func responseTwoDecodable<T: Decodable>(queue: DispatchQueue = DispatchQueue.global(qos: .userInitiated), of t: T.Type, completionHandler: @escaping (Result<T, APIError>) -> Void) -> Self {
        return response(queue: .main, responseSerializer: TwoDecodableResponseSerializer<T>()) { response in
            switch response.result {
            case .success(let result):
                completionHandler(result)
            case .failure(let error):
                completionHandler(.failure(APIError(message: "Other error", code: "other", args: [error.localizedDescription])))
            }
        }
    }
}

这样，我就可以这样调用我的API：

AF.request(request).validate().responseTwoDecodable(of: [Item].self) { response in
            switch response {
            case .success(let items):
                completion(.success(items))
            case .failure(let error): //error is an APIError
                log.error("Error while loading items: (String(describing: error))")
                completion(.failure(.couldNotLoad(underlyingError: error)))
            }
        }

我只是认为200-299范围之外的任何状态代码都对应于一个错误。

Answer 2

ResponseSerializer有一个单一的需求。在很大程度上，您可以只复制现有的序列化程序。例如，如果您想解析CSV(不进行响应检查(：

struct CommaDelimitedSerializer: ResponseSerializer {
    func serialize(request: URLRequest?, response: HTTPURLResponse?, data: Data?, error: Error?) throws -> [String] {
        // Call the existing StringResponseSerializer to get many behaviors automatically.
        let string = try StringResponseSerializer().serialize(request: request, 
                                                              response: response, 
                                                              data: data, 
                                                              error: error)
        
        return Array(string.split(separator: ","))
    }
}

您可以在Alamofire的文档中阅读更多信息。