c# - 底层连接已关闭 : An unexpected error occurred on a receive

Question

我在这里是因为我在通过 ftp 协议(protocol)下载一些文件时遇到了问题。这很奇怪，因为它偶尔会发生，甚至是针对同一个文件。

只是一个精度:我正在下载非常大的文件(从 500 Mo 到 30Go)

这是我的函数返回的异常类型:(抱歉，它是法语的)

System.Net.WebException: La connexion sous-jacente a été fermée:Une erreur inattendue s'est produite lors de la réception。 à System.Net.FtpWebRequest.CheckError() à System.Net.FtpWebRequest.SyncRequestCallback(Object obj) à System.IO.Stream.Close() à System.Net.ConnectionPool.Destroy(PooledStream pooledStream) à System.Net.ConnectionPool.PutConnection(PooledStream pooledStream, Object owningObject, Int32 creationTimeout, Boolean canReuse) à System.Net.FtpWebRequest.FinishRequestStage(RequestStage阶段) à System.Net.FtpWebRequest.SyncRequestCallback(Object obj) à System.Net.CommandStream.Abort(异常 e) à System.Net.CommandStream.CheckContinuePipeline() à System.Net.FtpDataStream.System.Net.ICloseEx.CloseEx(CloseExState closeState) à System.Net.FtpDataStream.Dispose( bool 处理) à System.IO.Stream.Close() à UtilityClasses.FTP.Download(String srcDirectoryPath, String file, String destDirectoryPath)

这是用于下载的代码:

下载方法:

public Dictionary<string, object> Download(string srcDirectoryPath, string file, string destDirectoryPath, int attemptLimitNb, int delay)
    {
        int attemptNb = 0;
        bool downloadFailed;
        Dictionary<string, object> result = new Dictionary<string,object>();

        do
        { 
            attemptNb++;
            result = Download(srcDirectoryPath, file, destDirectoryPath);
            downloadFailed = result["downloadfailed"] != null;
            if (downloadFailed) Thread.Sleep((int)(1000 * delay));
        }
        while (downloadFailed && attemptNb < attemptLimitNb);
        return result;
    }

public Dictionary<string, object> Download(string srcDirectoryPath, string file, string destDirectoryPath)
    {
        Exception downloadFailed = null;
        Dictionary<string, object> result = new Dictionary<string, object>();
        bool fileFound = false;

        try
        {
            if (destDirectoryPath == null || !Directory.Exists(destDirectoryPath)) throw new Exception("Download destination path does not exist");
            if (file != null && file != "")
            {
                if (file.Contains("/"))
                {
                    throw new Exception("Invalid file name. Impossible to download");
                }

                Uri serverUri;
                if (srcDirectoryPath == null || srcDirectoryPath == "")
                {
                    serverUri = new Uri("ftp://" + this.Server + "/" + file);
                }
                else if (Regex.IsMatch(srcDirectoryPath, "^/.*$") || Regex.IsMatch(srcDirectoryPath, "^.*/$"))
                {
                    throw new Exception("Path must not start and end with '/'");
                }
                else
                {
                    serverUri = new Uri("ftp://" + this.Server + "/" + srcDirectoryPath + "/" + file);
                }

                if (serverUri.Scheme != Uri.UriSchemeFtp) throw new Exception("server URI Scheme does not match  FTP URI Scheme");

                if (Exists(srcDirectoryPath, file))
                {
                    fileFound = true;

                    FtpWebRequest downloadRequest = (FtpWebRequest)FtpWebRequest.Create(serverUri);
                    downloadRequest.Credentials = new NetworkCredential(UserName, Password);
                    downloadRequest.KeepAlive = false;
                    downloadRequest.Method = WebRequestMethods.Ftp.DownloadFile;
                    FtpWebResponse response = (FtpWebResponse)downloadRequest.GetResponse();

                    Stream responseStream = response.GetResponseStream();
                    FileStream fileStream = new FileStream(Path.Combine(destDirectoryPath, file), FileMode.Create);
                    byte[] buffer = new byte[2000];
                    int read = 0;
                    try
                    {
                        do
                        {
                            read = responseStream.Read(buffer, 0, buffer.Length);
                            fileStream.Write(buffer, 0, read);
                            fileStream.Flush();
                        }
                        while (read != 0);
                    }
                    catch (Exception e)
                    {
                        fileStream.Close();
                        responseStream.Close();
                        response.Close();
                        throw e;
                    }
                    fileStream.Close();
                    responseStream.Close();
                    response.Close();
                }
            }
        }
        catch (WebException webExcptn)
        {
            downloadFailed = webExcptn;
        }
        finally
        {
            result.Add("filefound", fileFound);
            result.Add("downloadfailed", downloadFailed);
        }

        return result;
    }

Exists 方法:

public bool Exists(string srcPath, string elementName)
    {
        if (elementName == null || elementName == "")
        {
            return false;
        }

        Uri serverUri;
        bool res = false;

        if (srcPath == null || srcPath == "")
        {
            serverUri = new Uri("ftp://" + this.Server);
        }
        else if (Regex.IsMatch(srcPath, "^/.*$") || Regex.IsMatch(srcPath, "^.*/$"))
        {
            throw new Exception("Path must not start and end with '/'");
        }
        else
        {
            serverUri = new Uri("ftp://" + this.Server + "/" + srcPath);

        }
        if (serverUri.Scheme != Uri.UriSchemeFtp) throw new Exception("server URI Scheme does not match  FTP URI Scheme");

        FtpWebRequest listingRequest = (FtpWebRequest)FtpWebRequest.Create(serverUri);
        listingRequest.Credentials = new NetworkCredential(UserName, Password);
        listingRequest.KeepAlive = false;
        listingRequest.Method = WebRequestMethods.Ftp.ListDirectory;
        FtpWebResponse response = (FtpWebResponse)listingRequest.GetResponse();

        Stream responseStream = response.GetResponseStream();
        StreamReader streamReader = new StreamReader(responseStream);
        string ftpElementName;
        do
        {
            ftpElementName = Path.GetFileName(streamReader.ReadLine());
            if (ftpElementName == null) break;
            else
            {
                string pattern = "^" + elementName.Replace("[", "\\[").Replace("]", "\\]").Replace("+", "[+]").Replace(".", "[.]") + "$";
                if (Regex.IsMatch(ftpElementName, pattern, RegexOptions.IgnoreCase))
                {
                    res = true;
                }
            }
        }
        while (ftpElementName != null && !res);
        streamReader.Close();
        responseStream.Close();
        response.Close();

        return res;
    }

也许这是一个超时问题，但我真的不知道。我搜索了很长时间的答案但没有成功。也许你们中的一些人会有解决方案。

///

编辑:一些进展:

我已经使用 VS 在 Debug模式下测试了我的代码，实际上上面的异常是前一个异常的结果。 (我不知道，因为我只写了日志文件中返回的最后一个异常)

这是原始异常:

Unable to read data from the transport connection: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond.

第二个异常是Download方法这部分代码引起的:

catch (Exception e)
{
    fileStream.Close();
    responseStream.Close();  // <<<<<<<<<<<<<<
    response.Close();
    throw e;
}

我继续调查，但似乎“超时 pb”假设是最一致的。今晚我会尝试使用较大的超时值。

Answer 1

只是想加强ScottE的诊断，并且更加具体。超时很可能是问题所在。

FtpWebRequest 的 .Net 实现错误或 the MSDN document有错别字，FtpWebRequest.Timeout 的默认值不是-1(无限)。它是 100000(100 秒)。

另外还有一个超时问题。一些测试表明，responseStream 的超时值始终为 300000(300 秒)。我不知道这个值是如何分配的。无论如何，需要修改此值以适应大文件。

总而言之，解决方案是将 FtpWebRequest.Timeout 和 Stream.Timeout 设置为足够大的值。