Why does getting FileByte of uploaded file break StreamReader?

StackOverflow https://stackoverflow.com/questions/22568170

  •  19-06-2023
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Pergunta

I am working with a project in which I need to compare the byte representation of the file being uploaded to go ahead and check it against an accepted file size.

However, when the compiler executes byte[ ] filebyte = fileUpload.FileBytes the StreamReader stops functioning correctly.

Why is this behavior being caused, and is there a better way to accomplish what I am trying to do?

Below is a sample mockup of the issue.

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="FileUpload.aspx.cs" Inherits="TestASP.FileUpload" %>
<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="ajax" %>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
          <ajax:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server"></ajax:ToolkitScriptManager>
          <ajax:AsyncFileUpload  runat="server" ID="fileUpload" Width="300px" UploaderStyle="Modern" 
           BackColor="LightCoral" UploadingBackColor="#CCFFFF" ThrobberID="fileLoader" />
          <asp:Button ID="btUpload" runat="server" Text="Upload" OnClick="btUpload_Clicked" />
          <br />
          <asp:Label ID="lblMessage" runat="server" ForeColor="Green"></asp:Label>
          <br />
          <asp:Label ID="lblError" runat="server" ForeColor="Red"></asp:Label>
    </div>
    </form>
</body>
</html>



protected void Page_Load(object sender, EventArgs e)
{
    Page.Form.Attributes.Add("enctype", "multipart/form-data");
}
protected void btUpload_Clicked(object sender, EventArgs e)
{
    if(fileUpload.HasFile)
    {
        byte[] fileByte = fileUpload.FileBytes;
        StreamReader sr = new StreamReader(fileUpload.FileContent);
        TextReader tr = sr;
        String fileContent = tr.ReadToEnd();
        String fileName = Path.GetFileName(fileUpload.FileName);   
        this.lblMessage.Text = (fileContent);
    }
    else
    {
        this.lblError.Text = "File Not Uploaded";
    }
}
Foi útil?

Solução

You should decide for one way or the other, either use FileBytes or open the Stream using the FileContent property. I assume that FileBytes also reads the content of the Stream, so the StreamReader will start reading at the end - hence the empty output.

If you only want to check the size, you can do this using the PostedFile.ContentLength property:

if(fileUpload.HasFile)
{
    var sizeLimit = 1024 * 1024; // Limit to a megabyte
    if (fileUpload.PostedFile.ContentLength > sizeLimit)
        lblError.Tet = "File is too large";
    else
    {
        using(StreamReader sr = new StreamReader(fileUpload.FileContent))
        {
            String fileContent = sr.ReadToEnd();
            String fileName = Path.GetFileName(fileUpload.FileName);   
            this.lblMessage.Text = (fileContent);
        }
    }
}
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