NSURLSessionDownloadTask 文件在读取内容之前被移除

Question

我有以下一段代码，它已经工作了几个月并且刚刚开始间歇性地损坏。

我正在改变它被调用的方式，所以这并不完全不足为奇，但症状让我感到困惑。某些请求正在下载的临时文件似乎在读取数据之前被删除。

我有关于文件的属性，它的位置，当运行在模拟器中时，我什至在断点处确认文件包含正确的数据。但是，一旦 [NSData dataWithContentsOfFile:[location path]] 或 [NSData dataWithContentsOfURL:location] 被调用，文件就会从文件系统中删除，如果我使用传入 NSError 的方法，我得到的错误是 Error Domain=NSCocoaErrorDomain Code=260 "The operation couldn’t be completed.

我的代码：

- (void)makeSoapRequest:(NSURL *)url soapRequest:(NSString *)soapRequest completionBlock:(void (^)(NSData *xmlToParse, int error))completionBlock attemptNumber:(int)attemptNumber
{
    NSURLSessionConfiguration *sessionConfiguration = [NSURLSessionConfiguration defaultSessionConfiguration];
    NSURLSession *session = [NSURLSession sessionWithConfiguration:sessionConfiguration delegate:nil delegateQueue:nil];
    NSData *bodyData = [soapRequest dataUsingEncoding:NSUTF8StringEncoding];

    NSMutableURLRequest *request = [[NSMutableURLRequest alloc]initWithURL:url];
    [request setHTTPMethod:@"POST"];
    [request addValue:@"text/xml; charset=utf-8" forHTTPHeaderField:@"Content-Type"];
    [request addValue:@"" forHTTPHeaderField:@"SOAPAction"];
    [request addValue:[NSString stringWithFormat:@"%d",(int)[bodyData length]] forHTTPHeaderField:@"Content-Length"];
    [request setHTTPBody:bodyData];

    NSURLSessionDownloadTask *downloadTask = [session downloadTaskWithRequest:request completionHandler:^(NSURL *location, NSURLResponse *response, NSError *error) {
    if (!(location == nil))
    {
        dispatch_async(dispatch_get_main_queue(), ^{
            if (error)
            {
                NSLog(@"nsurl error was: %@", error);
            }
            else
            {
                NSError* errorObj;
                NSString *path = [location path];

                NSDictionary* attribs = [[NSFileManager defaultManager] attributesOfItemAtPath:path error:&errorObj];
                NSData *xmlData= [NSData dataWithContentsOfFile:path options:NSDataReadingMappedIfSafe error:&errorObj];
                if (errorObj != nil) {
                    NSLog(@"Attributes of file: %@", attribs);
                    NSLog(@"Error reading the downloaded data, error was: %@", errorObj);
                }
                completionBlock(xmlData, 0);
                return;
            }
        });
    }
    else
    {
        if (error)
        {
            dispatch_async(dispatch_get_main_queue(), ^{
                completionBlock(nil,-1);
            });
        }
        else
        {
            dispatch_async(dispatch_get_main_queue(), ^{
                completionBlock(nil,-1);
            });
        }
    }
}];
[downloadTask resume];
}

我的属性打印输出：

Attributes of file: {
NSFileCreationDate = "2016-11-23 13:15:00 +0000";
NSFileExtensionHidden = 0;
NSFileGroupOwnerAccountID = 501;
NSFileGroupOwnerAccountName = mobile;
NSFileModificationDate = "2016-11-23 13:15:00 +0000";
NSFileOwnerAccountID = 501;
NSFileOwnerAccountName = mobile;
NSFilePosixPermissions = 384;
NSFileReferenceCount = 1;
NSFileSize = 947;
NSFileSystemFileNumber = 534146;
NSFileSystemNumber = 16777218;
NSFileType = NSFileTypeRegular;
}

错误日志：

2016-11-23 13:27:43.285 GCMMobile[2780:829109] Error reading the downloaded data, error was: Error Domain=NSCocoaErrorDomain Code=260 "The operation couldn’t be completed. (Cocoa error 260.)" UserInfo=0x1704605c0 {NSFilePath=/private/var/mobile/Containers/Data/Application/BF6BE574-AA1A-492E-A1DD-04334F33E2D7/tmp/CFNetworkDownload_VHyKp6.tmp, NSUnderlyingError=0x17024ce10 "The operation couldn’t be completed. No such file or directory"}

非常感谢任何帮助...

Answer 1

问题是您在移动或打开下载的文件之前从 NSURLSessionDownloadTask 完成处理程序返回。正如 documentation 所述：

You must move this file or open it for reading before your completion handler returns. Otherwise, the file is deleted, and the data is lost.

通过分派到主队列并返回，您将文件读取代码推迟到未来某个不确定的时间。您应该在完成处理程序本身中移动或打开文件，然后才分派到另一个队列进行后续处理。

NSURLSessionDownloadTask 文件在读取内容之前被移除

NSURLSessionDownloadTask file removed before reading contents

ios

nsurlsessiondownloadtask