从 ftp 服务器下载文件到浏览器

Question

我正在创建一个 ASP.NET (VB.NET) 应用程序，该应用程序必须检索已知的远程文件并通过浏览器将其返回给访问者。我正在尝试使用位于此处的 Microsoft 示例：http://support.microsoft.com/?kbid=812406 并遇到错误“此流不支持查找操作”。我不确定如何继续。

这是标有错误行的代码。

Dim ftpWebReq As Net.FtpWebRequest = CType(Net.WebRequest.Create(path), Net.FtpWebRequest)
ftpWebReq.Method = Net.WebRequestMethods.Ftp.DownloadFile
ftpWebReq.KeepAlive = False
ftpWebReq.UsePassive = False
ftpWebReq.Credentials = New Net.NetworkCredential(System.Web.Configuration.WebConfigurationManager.AppSettings("FtpId"), System.Web.Configuration.WebConfigurationManager.AppSettings("FtpPwd"))
Dim ftpWebResp As Net.FtpWebResponse = CType(ftpWebReq.GetResponse(), Net.FtpWebResponse)
Dim streamer As Stream = ftpWebResp.GetResponseStream()

Dim buffer(10000) As Byte   ' Buffer to read 10K bytes in chunk:
Dim length As Integer       ' Length of the file:
Dim dataToRead As Long      ' Total bytes to read:
dataToRead = streamer.Length    ' *** This is the error line ***
Response.ContentType = "application/octet-stream"
Response.AddHeader("Content-Disposition", "attachment; filename=foo.txt")
While dataToRead > 0    ' Read the bytes.
If Response.IsClientConnected Then    ' Verify that the client is connected.
   length = streamer.Read(buffer, 0, 10000) ' Read the data in buffer
   Response.OutputStream.Write(buffer, 0, length)  ' Write the data to the current output stream.
   Response.Flush()        ' Flush the data to the HTML output.
   ReDim buffer(10000) ' Clear the buffer
   dataToRead = dataToRead - length
Else
   dataToRead = -1 'prevent infinite loop if user disconnects
End If
End While

Answer 1

不要打扰dataToRead。继续阅读直到 length 为 0（即 streamer.Read() 返回 0）。这意味着您已到达信息流的末尾。

我的 VB 有点生疏了，但我认为循环应该是这样的：

finished = False
While Not finished    ' Read the bytes.
    If Response.IsClientConnected Then    ' Verify that the client is connected.
        length = streamer.Read(buffer, 0, 10000) ' Read the data in buffer
        If length > 0 Then
            Response.OutputStream.Write(buffer, 0, length)  ' Write the data to the current output stream.
            Response.Flush()        ' Flush the data to the HTML output.
            ReDim buffer(10000) ' Clear the buffer
        Else
            finished = True
        End If
    Else
        finished = True
    End If
End While