使用URLSessionConfiguration.background和uploadTask上传文件错误处理

Question

我使用URLSessionConfiguration.background和uploadTask从iOS应用程序上传文件。

上载会话的配置方式如下：

let configuration = URLSessionConfiguration.background(withIdentifier: "com.mycompany.myapp.fileUploader")
configuration.isDiscretionary = false
configuration.allowsCellularAccess = true
uploadURLSession = URLSession(configuration: configuration, delegate: self, delegateQueue: nil)

请求是：

request.httpMethod = "POST"
request.setValue("application/octect-stream", forHTTPHeaderField: "Content-Type")


let task = uploadURLSession.uploadTask(with: request, fromFile: fileURL)

我想了解如何管理错误处理。

URLSession.uploadTask如何处理http错误4xx或5xx？

如何触发对5xx错误的重试？

Answer 1

URLSession.uploadTask不处理http服务器端错误。它只处理客户端或网络问题的重试和错误。

必须从任务响应中检索http状态/错误，将其转换为HTTPURLResponse。

直接来自uploadTask调用(背景URLSession不支持)：

let task = uploadSession?.uploadTask(with: request, fromFile: fileURL, completionHandler: { data, response, error in
    if let error = error {
        print("Upload error:\(error)")
        //Client side error
        return
    }
    
    guard let res = response as? HTTPURLResponse else {
        print("Upload completed with response:\(response.description ?? "undefined")")
        //It should not happen at all
        return
    }
    
    if (200...299).contains(res.statusCode) {
        print("Upload completed successfully. Status code:\(res.statusCode)")
    }
    else if (400...499).contains(res.statusCode) {
        print("Upload fatal issue. Status code:\(res.statusCode)")
        //Fatal issue, do not retry the upload
    }
    else if (500...599).contains(res.statusCode) {
        print("Upload issue. Status code:\(res.statusCode)")
        //Schedules a new uploading task for the file
    }
    else {
        print("Upload completed with status code:\(res.statusCode)")
    }
})

或者，如果您使用的是背景URLSession，则来自URLSessionTaskDelegate：

func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
    if let error = error {
        print("Upload error:\(error)")
        //Client side error
        return
    }

    guard let res = task.response as? HTTPURLResponse else {
        print("Upload completed with response:\(task.response?.description ?? "undefined")")
        //It should not happen at all
        return
    }

    if (200...299).contains(res.statusCode) {
        print("Upload completed successfully. Status code:\(res.statusCode)")
    }
    else if (400...499).contains(res.statusCode) {
        print("Upload fatal issue. Status code:\(res.statusCode)")
        //Fatal issue, do not retry the upload
    }
    else if (500...599).contains(res.statusCode) {
        print("Upload issue. Status code:\(res.statusCode)")
        //Schedules a new uploading task for the file
    }
    else {
        print("Upload completed with status code:\(res.statusCode)")
    }
}

Answer 2

创建这样的上传任务：

let task = uploadSession?.uploadTask(with: request, fromFile: fileURL, completionHandler: { data, response, error in
        if let error = error {
            print("Upload error: \(error.localizedDescription)")
        } else {
            if let response = response as? HTTPURLResponse {
                print("Response status code: \(response.statusCode)")
            }
        }
    })

    task?.resume()

您可以处理回调URLSessionTaskDelegate中的错误和responsecode，或者可以查看URLSessionDataDelegate和☝️，以获得对上传任务的细粒度控制。