How to Efficiently Upload and Download Files to/from an FTP Server in C#?

Uploading and downloading FTP server files in C#/.NET

Question 1: Streaming file upload

To avoid loading large files into memory before uploading, use FileStream and Stream.CopyTo to transfer files directly. The modified code is as follows:

<code class="language-csharp">using (Stream ftpStream = request.GetRequestStream())
using (Stream fileStream = File.OpenRead(@"/local/path/to/file.zip"))
{
    fileStream.CopyTo(ftpStream);
}</code>

Problem 2: The ZIP file is invalid after downloading

Confirm whether the FTP server supports pasv mode (passive mode data transfer) by enabling request.UsePassive = true. Additionally, set request.UseBinary = true to transfer files in binary mode. The modified code is as follows:

<code class="language-csharp">FtpWebRequest request =
    (FtpWebRequest)WebRequest.Create("ftp://ftp.example.com/remote/path/file.zip");
request.Credentials = new NetworkCredential("username", "password");
request.Method = WebRequestMethods.Ftp.DownloadFile;
request.UsePassive = true;
request.UseBinary = true;

using (Stream ftpStream = request.GetResponse().GetResponseStream())
using (Stream fileStream = File.Create(@"/local/path/to/file.zip"))
{
    ftpStream.CopyTo(fileStream);
}</code>

With the above modifications, you can successfully upload and download files to the FTP server, ensuring the integrity of the ZIP file after downloading.

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