依赖于afnetworking background sessi

NSString* filePath = [KDocumentPath stringByAppendingPathComponent:@"test.jpg"];
//
NSMutableURLRequest *request = [[AFHTTPRequestSerializer serializer] multipartFormRequestWithMethod:@"POST" URLString:urlString parameters:nil constructingBodyWithBlock:^(id<AFMultipartFormData> formData) {
[formData appendPartWithFileURL:[NSURL fileURLWithPath:filePath] name:@"uploadFile" fileName:@"filename.jpg" mimeType:@"application/octet-stream" error:nil];
[formData appendPartWithFormData:[frameIDString dataUsingEncoding:NSUTF8StringEncoding] name:@"frameID"];
[formData appendPartWithFormData:[deviceIdString dataUsingEncoding:NSUTF8StringEncoding] name:@"device_id"];

} error:nil];

NSString *appID = [[NSBundle mainBundle] bundleIdentifier];
NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier:appID];
_bgSession = [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:nil];

[[AFHTTPRequestSerializer serializer] requestWithMultipartFormRequest:request writingStreamContentsToFile:[NSURL fileURLWithPath:[KDocumentPath stringByAppendingPathComponent:@"aa"]] completionHandler:^(NSError * _Nullable error) {
    _task = [_bgSession uploadTaskWithRequest:request fromFile:[NSURL fileURLWithPath:[KDocumentPath stringByAppendingPathComponent:@"aa"]] ];
    [_task resume];
}];