当响应数据不包含要使用 Combine 解码的对象时，我如何抛出错误？

Question

我有一个发布者包装器结构，我可以在其中处理响应状态代码。如果状态代码不在 200..300 范围内，它会 return 对象，否则会抛出错误。效果很好。

public func anyPublisher<T:Decodable>(type: T.Type) -> AnyPublisher<T, Error> {
    return URLSession.shared.dataTaskPublisher(for: urlRequest)
        .tryMap { output in
            guard let httpResponse = output.response as? HTTPURLResponse, 200..<300 ~= httpResponse.statusCode else {
                throw APIError.unknown
            }
            return output.data
    }
    .decode(type: T.self, decoder: JSONDecoder())
    .receive(on: DispatchQueue.main)
    .eraseToAnyPublisher()
}

使用：

let sendNewUserPublisher = NetworkPublisher(urlRequest: request).anyPublisher(type: User.self)

cancellationToken = sendNewUserPublisher.sink(receiveCompletion: { completion in
    if case let .failure(error) = completion {
        NSLog("error: \(error.localizedDescription)")
    }
}, receiveValue: { post in
    self.post = post
})

如上，即使响应数据不包含要解码的对象，我也想处理错误。

public func anyPublisher() -> AnyPublisher<URLSession.DataTaskPublisher.Output, URLSession.DataTaskPublisher.Failure> {
    return URLSession.shared.dataTaskPublisher(for: urlRequest)
        // I'd like to handle status code here, and throw an error, if needed
        .receive(on: DispatchQueue.main)
        .eraseToAnyPublisher()
}

提前感谢您提供的任何帮助。

Answer 1

我建议创建一个 Publisher 来处理 HTTP 响应状态代码验证，并将其用于您的其他两个发布者 - 处理空请求正文的发布者和解码正文的发布者。

如果在验证其状态代码后仍需要 HTTPURLResponse 对象：

extension URLSession.DataTaskPublisher {
    /// Publisher that throws an error in case the data task finished with an invalid status code, otherwise it simply returns the body and response of the HTTP request
    func httpResponseValidator() -> AnyPublisher<Output, CustomError> {
        tryMap { data, response in
            guard let httpResponse = response as? HTTPURLResponse else { throw CustomError.nonHTTPResponse }
            let statusCode = httpResponse.statusCode
            guard (200..<300).contains(statusCode) else { throw CustomError.incorrectStatusCode(statusCode) }
            return (data, httpResponse)
        }
        .mapError { CustomError.network([=10=]) }
        .eraseToAnyPublisher()
    }
}

或者，如果您不关心响应的任何其他属性，只关心其状态代码是否有效：

func httpResponseValidator() -> AnyPublisher<Data, CustomError> {
    tryMap { data, response in
        guard let httpResponse = response as? HTTPURLResponse else { throw CustomError.nonHTTPResponse }
        let statusCode = httpResponse.statusCode
        guard (200..<300).contains(statusCode) else { throw CustomError.incorrectStatusCode(statusCode) }
        return data
    }
    .mapError { CustomError.network([=11=]) }
    .eraseToAnyPublisher()
}

然后您可以使用它来重写您的 anyPublisher 函数的两个版本：

extension URLSession.DataTaskPublisher {
    func anyPublisher<T:Decodable>(type: T.Type) -> AnyPublisher<T, Error> {
        httpResponseValidator()
            .decode(type: T.self, decoder: JSONDecoder())
            .receive(on: DispatchQueue.main)
            .eraseToAnyPublisher()
    }

    func anyPublisher() -> AnyPublisher<Output, CustomError> {
        httpResponseValidator()
            .receive(on: DispatchQueue.main)
            .eraseToAnyPublisher()
    }
}

当响应数据不包含要使用 Combine 解码的对象时，我如何抛出错误？

How could I throw an Error when response data does not contain an object to decode with Combine?

throw

swift

combine