在C#中从FTP读取文件到内存

Question

我想从FTP服务器读取文件而不将其下载到本地文件.我写了一个函数,但它不起作用:

private string GetServerVersion()
{
    WebClient request = new WebClient();

    string url = FtpPath + FileName;
    string version = "";

    request.Credentials = new NetworkCredential(ftp_user, ftp_pas);

    try
    {
        byte[] newFileData = request.DownloadData(new Uri(FtpPath)+FileName);
        string fileString = System.Text.Encoding.UTF8.GetString(newFileData);
    }
    catch (WebException e)
    {
    }
    return version;
}

Answer 1

这是一个简单的工作示例,使用您的代码从Microsoft公共FTP服务器获取文件:

WebClient request = new WebClient();
string url = "ftp://ftp.microsoft.com/developr/fortran/" +"README.TXT";
request.Credentials = new NetworkCredential("anonymous", "anonymous@example.com");

try
{
  byte[] newFileData = request.DownloadData(url);
  string fileString = System.Text.Encoding.UTF8.GetString(newFileData);
  Console.WriteLine(fileString);
}
catch (WebException e)
{
  // Do something such as log error, but this is based on OP's original code
  // so for now we do nothing.
}

我想你在代码中错过了这一行的斜杠:

string url = FtpPath + FileName;

也许在FtpPath和之间FileName？

Answer 2

小二进制文件

如果文件很小,最简单的方法是使用WebClient.DownloadData:

WebClient client = new WebClient();
string url = "ftp://ftp.example.com/remote/path/file.zip";
client.Credentials = new NetworkCredential("username", "password");
byte[] contents = client.DownloadData(url);

小文本文件

如果小文件是文本文件,请使用WebClient.DownloadString:

string contents = client.DownloadString(url);

它假定文件内容采用UTF-8编码(普通的ASCII文件也是如此).如果需要使用其他编码,请使用WebClient.Encodingproperty.

大二进制文件

如果文件很大,那么您需要以块的形式处理它,而不是将其加载到整个内存中,使用FtpWebRequest:

FtpWebRequest request =
    (FtpWebRequest)WebRequest.Create("ftp://ftp.example.com/remote/path/file.zip");
request.Credentials = new NetworkCredential("username", "password");
request.Method = WebRequestMethods.Ftp.DownloadFile;

using (Stream stream = request.GetResponse().GetResponseStream())
{
    byte[] buffer = new byte[10240];
    int read;
    while ((read = stream.Read(buffer, 0, buffer.Length)) > 0)
    {
        // process the chunk in "buffer"
    }
}

大文本文件

如果大文件是文本文件,并且您希望按行处理它,而不是按固定大小的块处理它,请使用StreamReader:

FtpWebRequest request =
    (FtpWebRequest)WebRequest.Create("ftp://ftp.example.com/remote/path/file.txt");
request.Credentials = new NetworkCredential("username", "password");
request.Method = WebRequestMethods.Ftp.DownloadFile;

using (Stream stream = request.GetResponse().GetResponseStream())
using (StreamReader reader = new StreamReader(stream))
{
    while (!reader.EndOfStream)
    {
        string line = reader.ReadLine();
        // process the line
        Console.WriteLine(line);
    }
}

同样,这假定UTF-8编码.如果要使用其他编码,请使用也需要的StreamReader构造函数重载Encoding.