WebClient将图像从URL下载到服务器C＃

Question

I have a dropbox public link that a user enters it in a textbox. Once the user clicks on a link the file should transfer to the location in the server. I ask the Dropbox forums and they mentioned that the Dropbox API is not necessary since is a public file.

https://www.dropbox.com/s/5y100bsknq7swdw/TestDoc.pdf?dl=1

Client Site

    <div id="testarea"></div>
     <div>
     @Html.TextBoxFor(x => x.HTML_text, new { id = "tbURL" })
     <input id="btnSubmit" type="button" value="Submit" onclick="btnSubmitClick()"/>
     </div>

     <script>

      function btnSubmitClick()
      {
        $.ajax({
        url: "/Home/SaveDocument",
        datatype: "text",
        data: { 'returnUrl': $('#tbURL').val() },
        type: "POST",
        success: function (data) {
            $('#testarea').html(data);
        },
        error: function () {
            $("#testarea").html("ERROR");
        }
       });

      }
      </script>

Server Side

        public string SaveDocument(string returnUrl)
        {
            using (var client = new WebClient())
            {
            //Not Working
              client.DownloadFile(returnUrl, "Test.pdf");
            }             
             return String.Format("Test03: String1={0};", returnUrl);
         }

Answer 1

The DownloadFile method will work so long as you specify a fully-qualified file name, which you have not. As an example, replacing "Test.pdf" with "C:\\\\Test.pdf" will download and save the file correctly. You, of course, need to make sure that the user context executing the server-side code has permission to write to the specified path.

If you want to write the file to a folder relative to your application's virtual directory, you can use the Server.MapPath method to get the folder path and then concatenate your file name to the end.