asp.net - 如何防止用户重新提交表单？

Question

我正在开发一个单页应用程序。

在应用程序结束时，用户可以提交他的联系信息(姓名、电话号码等)。这将发送一封电子邮件并将页面修改为“感谢提交 [...]”页面。

问题是，客户可以按返回按钮并重新发送电子邮件。

有没有办法防止这种……垃圾邮件？

代码

Sub BT_Send(sender As Object, e As EventArgs) Handles BT_Send.Click
Try
    'Creating the Email Message
    Dim mailMessage As New MailMessage()
    mailMessage.To.Add("SomeOne@a.com")
    mailMessage.From = New MailAddress("Robot@a.com", "Robot")
    mailMessage.Subject = "Test"
    mailMessage.IsBodyHtml = True
    mailMessage.Body = LBL_Emailbody.Text & _
        "<br><br><br><div style=""font-size: 0.7em;"">Robot speaking, I will not answer if you send me a message.</div>"
    Dim smtpClient As New SmtpClient("Something.com")
    smtpClient.Send(mailMessage)


    PNL_Before.Visible = False
    PNL_After.Visible = True
Catch ex As Exception
    LBL_errorEmail.Visible = True
    'Should never happen...
End Try
End sub

Answer 1

这是一个非常简单的示例，我在页面上使用静态变量并避免使用数据库。

asp.net 页面是

<asp:Literal runat="server" ID="txtInfos"></asp:Literal><br />
<asp:TextBox runat="server" ID="txtEmail"></asp:TextBox><br />
<asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="Button" />/>

以及背后的代码。

static Dictionary<string, DateTime> cLastSubmits = new Dictionary<string, DateTime>();

private static readonly object syncLock = new object();

protected void Button1_Click(object sender, EventArgs e)
{
    DateTime cWhenLast;

    lock (syncLock)
    {
        var cNowIs = DateTime.UtcNow;
        if (cLastSubmits.TryGetValue(txtEmail.Text, out cWhenLast))
        {
            if (cWhenLast > cNowIs )
            {
                txtInfos.Text = "Please contact us again after 10 seconds";
                return;
            }
            else
            {
                // ok I let him submit the form, but note the last date time.
                cLastSubmits.Remove(txtEmail.Text);
            }
        }

        foreach(var DelMe in cLastSubmits.Where(x => cNowIs > x.Value).ToList())
            cLastSubmits.Remove(DelMe.Key);

        // if reach here, note the last datetime of submit            
        cLastSubmits.Add(txtEmail.Text, cNowIs.AddSeconds(10));
    }

    // and submit the form.
    txtInfos.Text = "thank you for submit the form";
}

一些笔记。

• 如果你有很多池(网络花园)，那么这可能会让用户同时提交到您拥有的池。

• 当然，如果用户提交虚假数据，这将无法保护您，这就是我们可以使用的原因:

  1. honey pot trick .
  2. captcha
  3. 其他控制thats understands the bots
  4. 代码 that understand the re-submit .