ios - AFNetworking の予想される読み取りバイトは -1 です

Question

iPadからafnetworkingを使用してサーバーからファイルをダウンロードしようとしています。

ファイルを正常にダウンロードできます。しかし、不思議なことに、totalBytesRead は正しいのに、私の totalBytesExpectedToRead は常に -1 です。どこで間違えたのですか？

[operation setDownloadProgressBlock:^(NSUInteger bytesRead, long long totalBytesRead, long long totalBytesExpectedToRead)
{
}

コード全体はこちらです。

-(void)fileDownload : (NSString *)pathToDownload : (NSString *)fileExt
{
    hud = [MBProgressHUD showHUDAddedTo:self.view animated:YES];
    hud.mode = MBProgressHUDModeAnnularDeterminate;
    hud.labelText=@"Downloading...";

    NSLog(@"fileDownload and pathToDownload is %@",pathToDownload);

    NSArray *parts = [pathToDownload componentsSeparatedByString:@"\\"];
    NSString *fileName = [NSString stringWithFormat:@"%@",[parts objectAtIndex:[parts count]-1]];

    if([fileExt isEqualToString:@"pdf"])
    {
        fileNameForAllThreeFile=[fileName stringByDeletingPathExtension];
    }

    NSLog(@"fileName is %@",fileName);

    NSURL *url = [NSURL URLWithString:[NSString stringWithFormat:@"%@%@",IP_ADDRESS,download_recording]];

    AFHTTPClient *httpClient = [[AFHTTPClient alloc] initWithBaseURL:url];
    [httpClient setAuthorizationHeaderWithUsername:usernameForAuth password:passwordForAuth];

    NSDictionary *parameters = [NSDictionary dictionaryWithObjectsAndKeys:                            
                            pathToDownload,@"file",
                            nil];
    NSMutableURLRequest *request = [httpClient requestWithMethod:@"POST" path:download_recording parameters:parameters];

    AFHTTPRequestOperation *operation = [[AFHTTPRequestOperation alloc] initWithRequest:request];
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *path = [[paths objectAtIndex:0] stringByAppendingPathComponent:fileName];
    operation.outputStream = [NSOutputStream outputStreamToFileAtPath:path append:NO];

    [operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject)
    {
        NSString *responseStr = [[NSString alloc] initWithData:responseObject encoding:NSUTF8StringEncoding];
        NSLog(@"Request Successful in fileDownload, response '%@'", responseStr);

        NSLog(@"Successfully downloaded file to %@", path);
        [self messageDisplay:@"File download complete" :[NSString stringWithFormat:@"%@ download is now complete.",fileName]];
    } failure:^(AFHTTPRequestOperation *operation, NSError *error)
    {
        NSLog(@"Error in retrieveFromCustomServer: %@", error.localizedDescription);
        [self performSelectorInBackground:@selector(hideHUDInBackground) withObject:nil];

    }];
    [operation setDownloadProgressBlock:^(NSUInteger bytesRead, long long totalBytesRead, long long totalBytesExpectedToRead)
    {
        //do something in this line with the calculation to cell
        // float progress = (float)totalBytesRead / totalBytesExpectedToRead;
        NSLog(@"Downloaded %lld of %lld bytes", totalBytesRead, totalBytesExpectedToRead);
        float perCent = totalBytesRead / (float)totalBytesExpectedToRead;
        hud.progress = perCent ;
        NSLog(@"Percent is %d and in float is %f",(int)(perCent *100),perCent);
    }];
    [operation start];
}