在curl和C++中測量下載速度。我做得對嗎？

Question

我想弄清楚如何計算當前下載速度，同時下載許多文件的文件夾（它不是一個單一的文件，我正在下載）。而且我無法正確地做到這一點，現在經歷了好幾個小時，它變得太混亂了。下載速度有時會變得太高，有時它的0.

我正在使用curl和c + +。

在我的下載功能中，程序遞歸地下載每個文件，直到所有的文件都被下載。

這是我設置捲曲如何下載過程中調用TraceProgress功能：

curl_easy_setopt(curl, CURLOPT_PROGRESSFUNCTION, TraceProgress); 
curl_easy_setopt(curl, CURLOPT_PROGRESSDATA, &response); 
curl_easy_setopt(curl, CURLOPT_NOPROGRESS, 0); 

這裏是剩餘代碼：

double totalDownloadableSize = 0; // total size of the download, set prior to starting download of the first file 
    double downloadedSizeTillNow = 0; // total size downloaded till now - keep adding file size that just completed downloading 
    double currentDownloadingSize = 0; // size that we are downloading - downloadedSizeTillNow + bytes downloaded of the current file (in TraceProgress Function) 
    double oldDownloadNow = 0; // size of the old download bytes of that particular file 


    string fileDownloading = ""; 
    string tempFileDownloading = ""; 

    time_t startSeconds; 
    time_t oldSeconds; 

    int downloadIterationCounter = 0; 




    int TraceProgress(void *clientp, double dltotal, double dlnow, double ultotal, double ulnow) 
    { 

     // add size downloaded till now of this file to the total size downloaded till now 
     currentDownloadingSize = downloadedSizeTillNow + dlnow; 

     double rem = ((totalDownloadableSize - currentDownloadingSize)/1024)/1024; 

     // get current time in seconds 
     time_t currentSeconds = time (NULL); 

     // get elapsed time since last itiration 
     time_t secondsElapsedSinceLastItiration = currentSeconds - oldSeconds; 

     double downloadSinceLastIteration; 
     if (oldDownloadNow < dlnow)// so that we don't get wrong data when download file changes 
     { 
      downloadSinceLastIteration = dlnow - oldDownloadNow; 
     } 
     else 
     { 
      downloadSinceLastIteration = dlnow; 
     } 

     // calculate current download speed : (dlnow - oldNow)/(current time - oldTime) 
     double currentDownloadSpeed = downloadSinceLastIteration/(double)secondsElapsedSinceLastItiration; 


     // if downloading file name is not same as it was in the last call to this function 
     // change the display text and save the name in the temp. This approach will avoid unnecessory 
     // text change calls. 
     if (fileDownloading.compare(tempFileDownloading) != 0) 
     { 
      tempFileDownloading = fileDownloading; 
      string dlfilename = "Downloading: " + fileDownloading; 
      SetWindowText(hDownloadingSTATIC, dlfilename.c_str());// set text to static control 
     } 


     if (downloadIterationCounter == 4) 
     { 
      std::ostringstream strs_dn; 
      strs_dn << (unsigned int)(rem); 
      std::string downloadNow = strs_dn.str(); 


      string remSize = "Remaining: " + downloadNow + " MB"; 
      SetWindowText(hRemainingDownloadSTATIC, remSize.c_str());// set text to static control 


      double idownloadSpeed = currentDownloadSpeed/1024; 

      std::ostringstream strs_dnSp; 
      strs_dnSp << (unsigned int)(idownloadSpeed); 
      std::string downloadSpeed = strs_dnSp.str(); 

      string downSize = "Download Speed: " + downloadSpeed + " KB/s"; 
      SetWindowText(hDownloadSpeedSTATIC, downSize.c_str());// set text to static control 


      oldSeconds = currentSeconds;// save in old 
      oldDownloadNow = dlnow;// save in old 


      downloadIterationCounter = 0; 
     } 
     else 
     { 
      downloadIterationCounter++; 
     } 

     return 0; 
    } 

任何幫助表示讚賞。非常感謝。

Answer 1

dlnow - oldDownloadNow可能是錯的。您應該只使用dlnow。除非要顯示下載速度變化率，否則根本不需要oldDownloadNow。

_{I was confused by the `dltotal` and `dlnow` names. `dltotal` is the *expected* total bytes downloaded, and `dlnow` is bytes downloaded so far. So one does need `oldDownloadNow`, and `dlnow - oldDownloadNow` is the current delta.}

此片段

if (oldDownloadNow < dlnow) 
    { 
     downloadSinceLastIteration = dlnow - oldDownloadNow; 
    } 
    else 
    { 
     downloadSinceLastIteration = dlnow; 
    } 

有一個錯誤：oldDownloadNow == dlnow表示自上次沒有被下載。在這種情況下，當前的下載速度爲零。該片段應替換爲

downloadSinceLastIteration = dlnow - oldDownloadNow; 

沒有任何檢查。如果libcurl突然決定oldDownloadNow > dlnow，這將正確顯示負面下載速度，這是正確的做法。從不故意隱藏錯誤。

另外，time()分辨率太粗糙。使用某種細粒度的計時器。