Zero size files uploaded with FTP FileUpload

问题:

I've been reading gobs of articles on FTP upload in ASP.NET recently and they all seem to make sense, but every time I've tried implementing them I either get an empty file uploaded, or no file at all. Here are some of the articles I've been reading:

• Managing FTP Transfers from an ASP.NET Web Page By John Peterson
• FileUpload Control Doesn’t Give Full Path….HELP!!!!
• How to: Upload Files with the FileUpload Web Server Control

They're all great articles, but like I said, having issues :(

I know exactly what the problem is but I don't know how to fix it. I can pass the file name from the FileUpload control, but the path does not exist for security concerns. However, the StreamReader object requires the fully qualified path of the file to be uploaded, so how the heck do I get that? I'm at my wits end! >.<

Let's use the example by John Peterson that I linked above. Here's the code:

Protected Sub btnUploadFile_Click(ByVal sender As Object, ByVal e As System.EventArgs)
    Dim myFtpWebRequest As FtpWebRequest
    Dim myFtpWebResponse As FtpWebResponse
    Dim myStreamWriter As StreamWriter

    myFtpWebRequest = WebRequest.Create("ftp://ftp_server_name/filename.ext")
    myFtpWebRequest.Method = WebRequestMethods.Ftp.UploadFile
    myFtpWebRequest.UseBinary = True

    myStreamWriter = New StreamWriter(myFtpWebRequest.GetRequestStream())

    'IT BREAKS HERE BECAUSE THE CLIENT PATH IS WRONG!!
    myStreamWriter.Write(New StreamReader(Server.MapPath("filename.ext")).ReadToEnd)
    myStreamWriter.Close()

    myFtpWebResponse = myFtpWebRequest.GetResponse()
    myFtpWebResponse.Close()
End Sub

See? No data in the uploaded file :(

Now my latest implementation looks like this, but the uploaded file is much larger than the source, and corrupted. Seriously, what the heck am I doing wrong? I've been two LONG days at this, grrr...

Protected Sub btnUploadFile2_Click(ByVal sender As Object, ByVal e As System.EventArgs)
    Dim myFtpWebRequest As FtpWebRequest
    Dim myFtpWebResponse As FtpWebResponse

    filename = Path.GetFileName(FileUpload1.FileName)

    myFtpWebRequest = CType(WebRequest.Create(ftpServer + ftpPath + filename), FtpWebRequest)
    myFtpWebRequest.Method = WebRequestMethods.Ftp.UploadFile
    myFtpWebRequest.UseBinary = True

    'NEW APPROACH USING THE STREAM OF THE FILE FROM THE FileUpload Control
    'CORRECT BYTE LENGTH - in sourceStream.BaseStream
    Dim sourceStream As New StreamReader(FileUpload1.FileContent)
    'WRONG BYTE LENGTH - in sourceStream.ReadToEnd()
    Dim fileContents As Byte() = Encoding.UTF8.GetBytes(sourceStream.ReadToEnd())
    sourceStream.Close()
    myFtpWebRequest.ContentLength = fileContents.Length

    Dim requestStream As Stream = myFtpWebRequest.GetRequestStream()
    requestStream.Write(fileContents, 0, fileContents.Length)
    requestStream.Close()

    myFtpWebResponse = CType(myFtpWebRequest.GetResponse(), FtpWebResponse)
    myFtpWebResponse.Close()
End Sub

Thanks ever so much to Adam Maras for the amazing answer. I'll leave my blunders here for others to benefit who find this thread ;)

回答1:

First of all, you must upload through the web server if you're going to use ASP.NET like this. Without installing a plugin on the client's browser or using an ActiveX control (or similar) you absolutely cannot upload directly from the client machine to the FTP server.

I assume you're uploading binary files; if that's the case, the way you're using StreamReaders and StreamWriters could be corrupting the binary contents of the file. Instead, we can use the Stream.CopyTo method to move the data verbatim from one stream to the other.

I've modified your method to use this pattern instead:

Protected Sub btnUploadFile2_Click(ByVal sender As Object, ByVal e As System.EventArgs)
    Dim myFtpWebRequest As FtpWebRequest
    Dim myFtpWebResponse As FtpWebResponse

    filename = Path.GetFileName(FileUpload1.FileName)

    myFtpWebRequest = CType(WebRequest.Create(ftpServer + ftpPath + filename), FtpWebRequest)
    myFtpWebRequest.Method = WebRequestMethods.Ftp.UploadFile
    myFtpWebRequest.UseBinary = True

    Dim myFileStream As Stream = FileUpload1.FileContent
    myFtpWebRequest.ContentLength = myFileStream.Length

    Dim requestStream As Stream = myFtpWebRequest.GetRequestStream()
    myFileStream.CopyTo(requestStream)
    requestStream.Close()

    myFtpWebResponse = CType(myFtpWebRequest.GetResponse(), FtpWebResponse)
    myFtpWebResponse.Close()
End Sub

回答2:

The FileUpload.SaveAs() method saves to the Web server's local file system, and can't write to a URI or FTP site. To do that, you'll need to create a WebRequest.

See the MSDN reference for the FileUpload control here: http://msdn.microsoft.com/en-us/library/system.web.ui.webcontrols.fileupload.saveas.aspx

and for the FTP use of a WebRequest here: http://msdn.microsoft.com/en-us/library/ms229715.aspx

---

Note the example given in the FileUpload documentation saves to c:\temp\uploadedfiles. I'd suggest you use Path.GetTempFileName() instead as this is guaranteed to give you a file that can always be written no matter what environment you're under.

回答3:

The data gets corrupted because you are reading the file as if it was text, but it's not.

Use a BinaryReader instead of a StreamReader so that you can read the data as bytes directly:

Dim fileContents As Byte()
Using sourceStream As New StreamReader(FileUpload1.FileContent)
  fileContents = sourceStream.ReadBytes(Int32.MaxValue)
End Using