下载管理器 - 限制下载速度

Question

我需要为我的文件下载器应用程序实现下载速率限制，并且我查看了CodeProject的ThrottledStream类，但这不适用于我的情况，因为我必须能够在下载期间更改限制，而不仅仅是在开始时。这里的下载方法的一部分，我使用在后台线程：

webResponse = (HttpWebResponse)webRequest.GetResponse(); 
responseStream = webResponse.GetResponseStream(); 
responseStream.ReadTimeout = 5000; 

downloadCache = new MemoryStream(this.MaxCacheSize); 
byte[] downloadBuffer = new byte[this.BufferSize]; 
int bytesSize = 0; 
CachedSize = 0; 
int receivedBufferCount = 0; 

while (true) 
{ 
    bytesSize = responseStream.Read(downloadBuffer, 0, downloadBuffer.Length); 

    if (this.Status != DownloadStatus.Downloading || bytesSize == 0 
     || this.MaxCacheSize < CachedSize + bytesSize) 
    { 
     WriteCacheToFile(downloadCache, CachedSize); 

     this.DownloadedSize += CachedSize; 
     downloadCache.Seek(0, SeekOrigin.Begin); 
     CachedSize = 0; 

     if (this.Status != DownloadStatus.Downloading || bytesSize == 0) 
      break; 
    } 

    downloadCache.Write(downloadBuffer, 0, bytesSize); 
    CachedSize += bytesSize; 

    receivedBufferCount++; 
    if (receivedBufferCount == this.BufferCountPerNotification) 
    { 
     this.RaiseDownloadProgressChanged(); 
     receivedBufferCount = 0; 
    } 
} 

我已经使用了Thread.Sleep（）或Thread.Wait（），但它是一个好主意，也没见人？你有什么建议，我可以在这个while循环内做到这一点？

Answer 1

我已经使用这个代码从服务器下载文件可能是有帮助的，你......

private bool DownLoadFile(string pstrFileName, string pstrFilePath, long plngFileSize) 
    { 
     try 
     { 
      string strNewFileSize = CalcFileSize(plngFileSize); 
      int numIterations = 0; // this is used with a modulus of the sampleInterval to check if the chunk size should be adjusted. it is started at 1 so that the first check will be skipped because it may involve an initial delay in connecting to the web service 
      Offset = 0; 
      long webConfigSetting = this.mobjService.GetMaxRequestLength(); 
      this.MaxRequestLength = Math.Max(1, (webConfigSetting * 1024) - (2 * 1024)); // set the max buffer size to slightly less than the request length to allow for SOAP message headers etc. 
      if (File.Exists(pstrFilePath)) 
      { 
       Offset = new FileInfo(pstrFilePath).Length; 
       if (Offset == plngFileSize) 
        Offset = 0; 
       //File.Delete(pstrFilePath); 
      } 
      if (Offset == 0 && !File.Exists(pstrFilePath)) // create a new empty file 
       File.Create(pstrFilePath).Close(); 

      // open a file stream for the file we will write to in the start-up folder 
      lblFileName.Text = pstrFileName.Substring(0, pstrFileName.LastIndexOf(".")).Replace("&", "&&"); 
      using (FileStream fs = new FileStream(pstrFilePath, FileMode.OpenOrCreate, FileAccess.Write)) 
      { 
       pbrSummary.Maximum = (int)plngFileSize; 
       fs.Seek(Offset, SeekOrigin.Begin); 
       // download the chunks from the web service one by one, until all the bytes have been read, meaning the entire file has been downloaded. 
       while (Offset < plngFileSize) 
       { 
        int currentIntervalMod = numIterations % this.ChunkSizeSampleInterval; 
        if (currentIntervalMod == 0) 
         StartTime = DateTime.Now; // used to calculate the time taken to transfer the first 5 chunks 
        else if (currentIntervalMod == 1) 
         CalcAndSetChunkSize(plngFileSize); 
        try 
        { 
         // although the DownloadChunk returns a byte[], it is actually sent using MTOM because of the configuration settings. 
         byte[] Buffer = mobjService.DownloadChunk(pstrFileName, Offset, ChunkSize); 
         fs.Write(Buffer, 0, Buffer.Length); 
         Offset += Buffer.Length; // save the offset position for resume 
        } 
        catch (Exception ex) 
        { 
         if (ex.Message.Contains("File not found") || NumRetries++ >= MaxRetries) // too many retries, bail out 
         { 
          fs.Close(); 
          return false; 
          //throw new Exception("Error occurred during upload, too many retries.\r\n" + ex.Message); 
         } 
        } 
        numIterations++; 
        //----------------------- Code Commented ------------------------ 
        //lblDownload.Text = CalcFileSize(Offset) + " of " + strNewFileSize; 
        //lblRate.Text = CalcFileSize(ChunkSize)+"/sec"; 
        ////pbrSummary.Value = (int)Offset; 
        ////if ((int)Offset <= pbrSummary.Maximum) 
        //// pbrSummary.Value = (int)Offset; 
        ////else 
        //// pbrSummary.Value = pbrSummary.Maximum; 
        //------------------------------------------------------------------ 
       } 
      } 
      return true; 
     } 
     catch (Exception Exc) 
     { 
      throw (Exc); 
     } 
    } 
    private void CalcAndSetChunkSize(long plngFileSize) 
    { 
     /* chunk size calculation is defined as follows 
     *  in the examples below, the preferred transfer time is 1500ms, taking one sample. 
     *  
     *         Example 1         Example 2 
     *  Initial size    = 16384 bytes (16k)      16384 
     *  Transfer time for 1 chunk = 800ms          2000 ms 
     *  Average throughput/ms  = 16384b/800ms = 20.48 b/ms    16384/2000 = 8.192 b/ms 
     *  How many bytes in 1500ms? = 20.48 * 1500 = 30720 bytes    8.192 * 1500 = 12228 bytes 
     *  New chunksize    = 30720 bytes (speed up)     12228 bytes (slow down from original chunk size) 
     */ 
     double transferTime = DateTime.Now.Subtract(this.StartTime).TotalMilliseconds; 
     double averageBytesPerMilliSec = this.ChunkSize/transferTime; 
     double preferredChunkSize = averageBytesPerMilliSec * this.PreferredTransferDuration; 
     this.ChunkSize = (int)Math.Min(this.MaxRequestLength, Math.Max(4 * 1024, preferredChunkSize)) * 10; // set the chunk size so that it takes 1500ms per chunk (estimate), not less than 4Kb and not greater than 4mb // (note 4096Kb sometimes causes problems, probably due to the IIS max request size limit, choosing a slightly smaller max size of 4 million bytes seems to work nicely)   

     //string statusMessage = String.Format("Chunk size: {0}{1}", CalcFileSize(this.ChunkSize), (this.ChunkSize == this.MaxRequestLength) ? " (max)" : ""); 
    }