handle memory issue

Author: YangSen-qn

QiniuSDK/Http/Request/HttpClient/QNUploadSystemClient.m

@@ -62,9 +62,12 @@ - (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)data
 }
 
 - (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(nullable NSError *)error {
-    
+    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:task.currentRequest.URL
+                                                           cachePolicy:task.currentRequest.cachePolicy
+                                                       timeoutInterval:task.currentRequest.timeoutInterval];
+    request.allHTTPHeaderFields = task.currentRequest.allHTTPHeaderFields;
     self.requestMetrics.endDate = [NSDate date];
-    self.requestMetrics.request = task.currentRequest;
+    self.requestMetrics.request = [request copy];
     self.requestMetrics.response = task.response;
     self.requestMetrics.countOfResponseBodyBytesReceived = task.response.expectedContentLength;
     self.requestMetrics.countOfRequestHeaderBytesSent = [NSString stringWithFormat:@"%@", task.currentRequest.allHTTPHeaderFields].length;