C＃ - FtpWebRequest - 通过同一连接/登录的多个请求

Question

I want to loop on a FTP folder for check if a file has arrived

I do:

FtpWebRequest request = (FtpWebRequest)WebRequest.Create("ftp://localhost:8080");
request.Credentials = new NetworkCredential("anonymous", "");
request.Method = WebRequestMethods.Ftp.ListDirectoryDetails;

while(true)
{
    using (FtpWebResponse response = (FtpWebResponse)request.GetResponse())
    using (Stream responseStream = response.GetResponseStream())
    using (StreamReader reader = new StreamReader(responseStream))
    {
        Console.WriteLine(reader.ReadToEnd());

        reader.Close();
        response.Close();
    }
}

But at the second iteration I get an exception:

The stream cannot be read

Answer 1

Sorry, I missed it, you're only issuing one request and trying to get a response multiple times. Try the code below:

while(true)
{
    FtpWebRequest request =     (FtpWebRequest)WebRequest.Create("ftp://localhost:8080");
    request.Credentials = new NetworkCredential("anonymous", "");
    request.Method = WebRequestMethods.Ftp.ListDirectoryDetails;

    using (FtpWebResponse response = (FtpWebResponse)request.GetResponse())
    using (Stream responseStream = response.GetResponseStream())
    using (StreamReader reader = new StreamReader(responseStream))
    {
        Console.WriteLine(reader.ReadToEnd());

        reader.Close();
        response.Close();
    }
}

You should add a pause of some sort at the end of each loop though. You don't want to bombard the server.

Answer 2

You cannot reuse the FtpWebRequest instance for multiple requests.

But as the FtpWebRequest works on top of a connection pool, it actually can reuse an underlying FTP connection. As long as the FtpWebRequest.KeepAlive is set to its default value of true .

When the KeepAlive is set to true , the underlying FTP connection is not closed, when the request finishes. When you create another instance of the FtpWebRequest with the same URL, the connection is reused.

while (true)
{
    FtpWebRequest request = (FtpWebRequest)WebRequest.Create("ftp://localhost:8080");
    request.Credentials = new NetworkCredential("anonymous", "");
    request.Method = WebRequestMethods.Ftp.ListDirectoryDetails;
    // reuse the connection (not necessary, as the true is the default)
    request.KeepAlive = true;

    using (FtpWebResponse response = (FtpWebResponse)request.GetResponse())
    using (Stream responseStream = response.GetResponseStream())
    using (StreamReader reader = new StreamReader(responseStream))
    {
        Console.WriteLine(reader.ReadToEnd());

        reader.Close();
        response.Close();
    }
}