C# Can'；尝试使用WebClient.DownloadFile（）或WebRequest下载文件时无法实现超时

我正在尝试实现一些从URL下载文件的功能。但是，如果文件占用的时间超过30秒，我想取消下载，或者让它超时

我已经尝试重写WebClient类来实现超时，但是无论我将超时设置为什么值，它都不会超时！这是我试过的代码：

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我还尝试使用WebRequest方法下载文件，并使用Timeout和ReadWriteTimeout属性，但没有骰子。这必须是一个非常常见的用例。感谢您的帮助。谢谢

您实现的超时与获取响应有关，但与包含所有数据的ResponseStream无关，通常需要更多时间才能实现。例如，获取响应通常需要不到1秒的时间，但下载网页内容可能需要几秒钟

至于下载文件，您可以使用

HttpWebRequest

获取

HttpWebResponse

并从中使用方法

GetResponseStream（）

获取数据流

这将有助于：

尤其是

byte[]buffer

用于获取部分数据的部分，而不是

StreamReader

ReadToEnd（）

方法。在将部分数据下载到缓冲区时，您可以根据超时日期时间检查当前日期时间，从而允许在超时日期时间之后取消下载

编辑：一段有用的代码

private byte[] DownloadFile( string uri, int requestTimeout, int downloadTimeout, out bool isTimeout, out int bytesDownloaded )
{
    HttpWebRequest request = WebRequest.Create( uri ) as HttpWebRequest;
    request.Timeout = requestTimeout;
    HttpWebResponse response = null;
    Stream responseStream = null;
    MemoryStream downloadedData = null;

    byte[] result = null;
    bytesDownloaded = 0;

    isTimeout = false;
    try
    {
        // Get response
        response = request.GetResponse() as HttpWebResponse;
        byte[] buffer = new byte[ 16384 ];

        // Create buffer for downloaded data
        downloadedData = new MemoryStream();

        // Set the timeout
        DateTime timeout = DateTime.Now.Add( new TimeSpan( 0, 0, 0, 0, downloadTimeout ) );

        // Read parts of the stream
        responseStream = response.GetResponseStream();
        int bytesRead = 0;
        DateTime now = DateTime.Now;
        while ( (bytesRead = responseStream.Read( buffer, 0, buffer.Length )) > 0 && DateTime.Now < timeout )
        {
            downloadedData.Write( buffer, 0, bytesRead );
            now = DateTime.Now;
            bytesDownloaded += bytesRead;
        }

        // Notify if timeout occured (could've been written better)
        if ( DateTime.Now >= timeout )
        {
            isTimeout = true;
        }
    }
    catch ( WebException ex )
    {
        // Grab timeout exception
        if ( ex.Status == WebExceptionStatus.Timeout )
        {
            isTimeout = true;
        }
    }
    finally
    {
        // Close the stream
        if ( responseStream != null )
        {
            responseStream.Close();
        }
    }

    if ( downloadedData != null )
    {
        result = downloadedData.GetBuffer();
        downloadedData.Close();
    }

    return result;
}

---

记住，对于您可能遇到的其他异常，此代码仍然容易受到攻击。

创建扩展方法如何

WebClient wc = new WebClient();
wc.DownloadFileWithTimeout(url, filename, 20000);

公共静态类SOExtensions
{
public static void DownloadFileWithTimeout（此WebClient wc、字符串url、字符串文件、int timeout）
{
var tcs=new TaskCompletionSource（）；
var bgTask=Task.Factory.StartNew（（）=>
{
DownloadFileTaskAsync（url，file）.Wait（）；
tcs.TrySetResult（真）；
});
如果（！bgTask.Wait（超时））
{
wc.CancelAsync（）；
抛出新的TimeoutException（“下载\'+url+“\””时超时）；
}
}
}

我尝试了你的代码，没有发现任何问题。正如您所期望的那样超时。我在HttpWebRequest上单独使用超时时遇到了各种问题，因为它没有涵盖有关下载实际数据的超时。OP的代码在我的机器上也不能正常工作。它尝试下载整个文件（测试下载6MB文件时超时为500ms，OP的方法下载需要1800ms）。

private byte[] DownloadFile( string uri, int requestTimeout, int downloadTimeout, out bool isTimeout, out int bytesDownloaded )
{
    HttpWebRequest request = WebRequest.Create( uri ) as HttpWebRequest;
    request.Timeout = requestTimeout;
    HttpWebResponse response = null;
    Stream responseStream = null;
    MemoryStream downloadedData = null;

    byte[] result = null;
    bytesDownloaded = 0;

    isTimeout = false;
    try
    {
        // Get response
        response = request.GetResponse() as HttpWebResponse;
        byte[] buffer = new byte[ 16384 ];

        // Create buffer for downloaded data
        downloadedData = new MemoryStream();

        // Set the timeout
        DateTime timeout = DateTime.Now.Add( new TimeSpan( 0, 0, 0, 0, downloadTimeout ) );

        // Read parts of the stream
        responseStream = response.GetResponseStream();
        int bytesRead = 0;
        DateTime now = DateTime.Now;
        while ( (bytesRead = responseStream.Read( buffer, 0, buffer.Length )) > 0 && DateTime.Now < timeout )
        {
            downloadedData.Write( buffer, 0, bytesRead );
            now = DateTime.Now;
            bytesDownloaded += bytesRead;
        }

        // Notify if timeout occured (could've been written better)
        if ( DateTime.Now >= timeout )
        {
            isTimeout = true;
        }
    }
    catch ( WebException ex )
    {
        // Grab timeout exception
        if ( ex.Status == WebExceptionStatus.Timeout )
        {
            isTimeout = true;
        }
    }
    finally
    {
        // Close the stream
        if ( responseStream != null )
        {
            responseStream.Close();
        }
    }

    if ( downloadedData != null )
    {
        result = downloadedData.GetBuffer();
        downloadedData.Close();
    }

    return result;
}

private void button1_Click( object sender, EventArgs e )
{
    bool isTimeout;
    int bytesDownloaded;
    byte[] data = DownloadFile( something, 1000,500, out isTimeout, out bytesDownloaded );

    MessageBox.Show( "Downloaded " + bytesDownloaded.ToString() + " bytes, Timeout = " + isTimeout.ToString() );
}

WebClient wc = new WebClient();
wc.DownloadFileWithTimeout(url, filename, 20000);

public static class SOExtensions
{
    public static void DownloadFileWithTimeout(this WebClient wc, string url, string file, int timeout)
    {
        var tcs = new TaskCompletionSource<bool>();

        var bgTask = Task.Factory.StartNew(() =>
        {
            wc.DownloadFileTaskAsync(url, file).Wait();
            tcs.TrySetResult(true);
        });


        if (!bgTask.Wait(timeout))
        {
            wc.CancelAsync();
            throw new TimeoutException("Timed out while downloading \"" + url + "\"");
        }
    }
}