swift - 如何处理等待嵌套 URLSession 完成的情况

Question

我有一个函数可以在 URLSession 上提供一个层。调用此函数时，我想检查当前访问 token 是否已过期，如果已过期，我将暂停当前调用，进行调用以请求新 token ，替换钥匙串(keychain)中的现有条目，然后继续电话。

func profile(with endpoint: ProfilesEndpoint, method: HTTPMethod, body: String?, headers: [String: String]?, useAuthToken: Bool = true, completion: @escaping (Either<ProfileResponse>) -> Void) {
    var request = endpoint.request
    request.httpMethod = method.rawValue

    if let body = body {
        request.httpBody = body.data(using: .utf8)
    }

    if useAuthToken {
        if !AuthService.shared.isTokenValid {
            let group = DispatchGroup()
            group.enter()
                OAuthService.shared.requestRefreshToken()
            group.leave()
        }

        let (header, token) = AuthService.shared.createAuthHeaderForNetworkRequest()
        request.addValue(token, forHTTPHeaderField: header)
    }

    if let headers = headers {
        for (key, value) in headers {
            request.addValue(value, forHTTPHeaderField: key)
        }
    }

    execute(with: request, completion: completion)
}

存在用于处理钥匙串(keychain)的机制，因此请假定该机制已就位。

请求新 token 的函数如下所示

func requestRefreshToken() -> Void {

    if let refreshToken = KeychainWrapper.standard.string(forKey: "RefreshToken") {

        var postBody = "grant_type=\(refreshTokenGrantType)&"
        postBody += "client_id=\(clientId)&"
        postBody += "refresh_token=\(refreshToken)&"

        let additionalHeaders = [
            "Content-Type": "application/x-www-form-urlencoded;"
        ]

        APIClient.shared.identity(with: .token, method: .post, body: postBody, headers: additionalHeaders, useAuthToken: false) { either in
            switch either {
            case .success(let results):
                guard let accessToken = results.accessToken, let refreshToken = results.refreshToken else { return }
                AuthService.shared.addTokensToKeyChain(tokens: ["AccessToken": accessToken, "RefreshToken": refreshToken])
            case .error(let error):
                print("Error:", error)
            }
        }
    }
}

我期待执行在这里暂停

     group.enter()
            OAuthService.shared.requestRefreshToken()
        group.leave()

然而事实并非如此。

如何在完成函数的其余部分之前等待此调用完成？

Answer 1

添加到您的 requestRefreshToken 方法完成处理程序中，该处理程序将在您的 token 请求完成时执行

func requestRefreshToken(_ completion: @escaping () -> Void) {

    if let refreshToken = KeychainWrapper.standard.string(forKey: "RefreshToken") {

        var postBody = "grant_type=\(refreshTokenGrantType)&"
        postBody += "client_id=\(clientId)&"
        postBody += "refresh_token=\(refreshToken)&"

        let additionalHeaders = [
            "Content-Type": "application/x-www-form-urlencoded;"
        ]

        APIClient.shared.identity(with: .token, method: .post, body: postBody, headers: additionalHeaders, useAuthToken: false) { either in

            switch either {
            case .success(let results):
                guard let accessToken = results.accessToken, let refreshToken = results.refreshToken else { 
                    completion()
                    return 
                }
                AuthService.shared.addTokensToKeyChain(tokens: ["AccessToken": accessToken, "RefreshToken": refreshToken])
            case .error(let error):
                print("Error:", error)
            }

            completion()
        }
    }
}

然后将 dispatchGroup 保留在闭包中，并添加 group.wait() (在调用请求方法之后)用于暂停当前线程，直到组的任务完成

group.enter()
    OAuthService.shared.requestRefreshToken {
        group.leave()
    }
group.wait()

注意:您可以在完成中添加 bool 参数来检查 token 请求是否成功