Swift中UrlRequest的JSON编码问题：请求体格式异常

我正在搭建一个API服务，编写了如下登录请求代码：

enum HttpMethod: Equatable {
    case get([URLQueryItem])
    case put(Data?)
    case post(Data?)

    var name: String {
        switch self {
        case .get: return "GET"
        case .put: return "PUT"
        case .post: return "POST"
        }
    }
}

struct Request<Response> {
    let url: URL
    let method: HttpMethod
    var headers: [String: String] = [:]
}

extension Request {
    static func postUserLogin(email: String, password:String) -> Self {
        var params = [String: Any]()
        params["username"] = email
        params["password"] = password
        let data = params.jsonData

        return Request(
            url: URL(string: NetworkingConstants.USER_LOGIN)!,
            method: .post(
                try? JSONEncoder().encode(data) //should this be something else???
            )
        )
    }
}

extension Dictionary {
    var jsonData: Data? {
        return try? JSONSerialization.data(withJSONObject: self, options: [.prettyPrinted])
    }
}

extension Request {
    var urlRequest: URLRequest {
        var request = URLRequest(url: url)

        switch method {
        case .post(let data), .put(let data):
            request.httpBody = data

        case let .get(queryItems):
            //removed for brevity
        default:
            break
        }

        request.setValue("application/json", forHTTPHeaderField: "Content-Type")
        request.allHTTPHeaderFields = headers
        request.httpMethod = method.name
        return request
    }
}

extension URLSession {
    func decode<Value: Decodable>(
        _ request: Request<Value>,
        using decoder: JSONDecoder = .init()
    ) async throws -> Value {
        let decoded = Task.detached(priority: .userInitiated) {
            let (data, _) = try await self.data(for: request.urlRequest)
            try Task.checkCancellation()
            return try decoder.decode(Value.self, from: data)
        }
        return try await decoded.value
    }
}

问题在于，发送给服务器的请求体并非预期的JSON格式：

{
    "username": "me@you.com",
    "password": "abcdef"
}

而是变成了Base64编码字符串：

"eyJwYXNzd29yZCI6ImFhYWEiLCJ1cZSI6InRhQHQuY29tIn0="

我通过以下方式发起请求：

let request: Request<UserLoginResponse> = .postUserLogin(email: "me@you.com", password: "abcdef")
let response = try? await URLSession.shared.decode(request)

请求的httpBody信息如下：

▿ Optional<Data>
  ▿ some : 74 bytes
    - count : 74
    ▿ pointer : 0x00007fcc74011200
      - pointerValue : 140516096283136

请问我哪里出错了？

核心错误 #

你犯了重复编码的问题：

1. 第一步通过params.jsonData已经把字典序列化成了JSON格式的Data，这一步是正确的；
2. 但你又用JSONEncoder().encode(data)去编码这个Data对象——JSONEncoder处理Data类型时，默认会将其转为Base64字符串，最终导致请求体变成了Base64编码后的内容，而非原始JSON。

修复代码 #

直接使用params.jsonData作为POST请求的body即可，去掉多余的JSONEncoder编码步骤：

extension Request {
    static func postUserLogin(email: String, password:String) -> Self {
        var params = [String: Any]()
        params["username"] = email
        params["password"] = password
        
        return Request(
            url: URL(string: NetworkingConstants.USER_LOGIN)!,
            method: .post(params.jsonData)
        )
    }
}

额外优化建议 #

• 避免强制解包URL(string:)，添加可选绑定处理，防止URL无效导致崩溃；
• 建议用Codable协议替代JSONSerialization，类型更安全：比如定义一个LoginParams结构体，直接用JSONEncoder编码，比[String:Any]更可靠。示例如下：

struct LoginParams: Encodable {
    let username: String
    let password: String
}

extension Request {
    static func postUserLogin(email: String, password:String) -> Self? {
        guard let url = URL(string: NetworkingConstants.USER_LOGIN) else {
            return nil
        }
        let params = LoginParams(username: email, password: password)
        let data = try? JSONEncoder().encode(params)
        
        return Request(
            url: url,
            method: .post(data)
        )
    }
}

内容的提问来源于stack exchange，提问作者soleil