How can I recursively download files and subdirectories from an FTP server using C#?

Use C# to recursively download files and subdirectories on an FTP server

Question:

The current code only lists and downloads files in the specified FTP directory, but cannot download subdirectories and subfiles. Additionally, when trying to download the folder as a file, the server returns a 550 error.

Solution:

Implement recursive directory listing and download operations:

Recursive directory listing:

1. List remote directories using protocol-specific commands such as LIST or MLSD.
2. Parse directory listings to identify files and directories.
3. If the entry is a file, use the DownloadFile method to download it.
4. If the entry is a directory, recursively list and download its contents.

Identify files from subdirectories:

Since FtpWebRequest has no explicit way to achieve this, the alternative is:

• Attempt an operation that is valid for files but not for directories (e.g., DownloadFile).
• Identifies files based on filename patterns (e.g. all files have an extension).
• Use server-specific directory listing format (e.g. look for a directory with a "d" at the beginning of the line in a Unix-style listing).

Example recursive download code:

<code class="language-csharp">void DownloadFtpDirectory(string url, NetworkCredential credentials, string localPath)
{
    // 列出目录详细信息
    FtpWebRequest listRequest = (FtpWebRequest)WebRequest.Create(url);
    listRequest.Method = WebRequestMethods.Ftp.ListDirectoryDetails;
    listRequest.Credentials = credentials;

    var lines = new List<string>();
    using (var listResponse = (FtpWebResponse)listRequest.GetResponse())
    using (var listStream = listResponse.GetResponseStream())
    using (var listReader = new StreamReader(listStream))
    {
        while (!listReader.EndOfStream)
        {
            lines.Add(listReader.ReadLine());
        }
    }

    // 迭代目录条目
    foreach (var line in lines)
    {
        var tokens = line.Split(' ', 9, StringSplitOptions.RemoveEmptyEntries);
        var name = tokens[8];
        var permissions = tokens[0];

        var localFilePath = Path.Combine(localPath, name);
        var fileUrl = url + name + "/";

        // 如果是目录，则递归
        if (permissions[0] == 'd')
        {
            if (!Directory.Exists(localFilePath))
            {
                Directory.CreateDirectory(localFilePath);
            }

            DownloadFtpDirectory(fileUrl, credentials, localFilePath);
        }
        // 如果是文件，则下载
        else
        {
            var downloadRequest = (FtpWebRequest)WebRequest.Create(fileUrl);
            downloadRequest.Method = WebRequestMethods.Ftp.DownloadFile;
            downloadRequest.Credentials = credentials;

            using (FtpWebResponse downloadResponse = (FtpWebResponse)downloadRequest.GetResponse())
            using (var sourceStream = downloadResponse.GetResponseStream())
            using (var targetStream = File.Create(localFilePath))
            {
                // 传输文件数据
                byte[] buffer = new byte[10240];
                int read;
                while ((read = sourceStream.Read(buffer, 0, buffer.Length)) > 0)
                {
                    targetStream.Write(buffer, 0, read);
                }
            }
        }
    }
}</code>

Usage:

<code class="language-csharp">var credentials = new NetworkCredential("user", "password");
var url = "ftp://ftp.example.com/directory/to/download/";
var localPath = @"C:\target\directory";
DownloadFtpDirectory(url, credentials, localPath);</code>

Alternatively, consider using a third-party library like WinSCP, which supports recursive directory operations and can handle various FTP server formats.

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