我在这里因为在使用FTP协议下载某些文件时遇到了问题。很奇怪，因为它偶尔发生，即使是对于同一个文件。
只是要说明一下：我正在下载非常大的文件（从500Mo到30Go）
以下是由我的函数返回的异常类型:（抱歉，是用法语写的）
System.Net.WebException: 连接已关闭：在接收时发生了意外错误。
at System.Net.FtpWebRequest.CheckError()
at System.Net.FtpWebRequest.SyncRequestCallback(Object obj)
at System.IO.Stream.Close()
at System.Net.ConnectionPool.Destroy(PooledStream pooledStream)
at System.Net.ConnectionPool.PutConnection(PooledStream pooledStream, Object owningObject, Int32 creationTimeout, Boolean canReuse)
at System.Net.FtpWebRequest.FinishRequestStage(RequestStage stage)
at System.Net.FtpWebRequest.SyncRequestCallback(Object obj)
at System.Net.CommandStream.Abort(Exception e)
at System.Net.CommandStream.CheckContinuePipeline()
at System.Net.FtpDataStream.System.Net.ICloseEx.CloseEx(CloseExState closeState)
at System.Net.FtpDataStream.Dispose(Boolean disposing)
at System.IO.Stream.Close()
at UtilityClasses.FTP.Download(String srcDirectoryPath, String file, String destDirectoryPath)
以下是用于下载的代码：
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;
}
the Exists method :
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，但我真的不确定。我搜索了很久，但没有找到答案。也许你们中的一些人会有解决方案。
///
编辑：有一些进展：
我已经在VS的调试模式下测试了我的代码，实际上上面的异常是先前异常的结果。（我不知道这一点，因为我只把最后一个返回的异常写入了日志文件）
这是原始的异常：
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.
第二个异常是由Download方法代码中的这部分引起的：
catch (Exception e)
{
fileStream.Close();
responseStream.Close(); // <<<<<<<<<<<<<<
response.Close();
throw e;
}
我继续进行调查，但似乎“超时问题”假设是最一致的。今晚我会尝试使用更长的超时时间。