Length cannot be less than zero error occured at 4th and 5th line

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1 string userIP = Request.UserHostAddress;
2 string serverIP = Request.ServerVariables["LOCAL_ADDR"];
3
4 userIP = userIP.Substring(0, userIP.LastIndexOf("."));
5 serverIP = serverIP.Substring(1, serverIP.LastIndexOf("."));

C#

// only redirect to WinLogin.aspx if user is internal & IE
 if (userIP.Equals(serverIP) && Request.Browser.IsBrowser("ie"))
  {
     Server.Transfer("SecondLogin.aspx"");
  }
else
  {
     Server.Transfer("ThirdLogin.aspx"");
  }

Posted 2-Dec-14 21:52pm

Member 11270220

Updated 2-Dec-14 22:04pm

/\jmot

v2

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Badal Kumar · Answer 1 · 2014-12-02T21:57:00

Solution 1

What values coming inside userIP and serverIP.

Put a check if length is greater then 0 then only execute the substring statement.

Posted 2-Dec-14 21:57pm

Badal Kumar

Abhinav S · Answer 2 · 2014-12-02T21:57:00

Solution 2

userIP.Substring(0, userIP.LastIndexOf("."));
LastIndexOf returns -1 if text is not found.

In your case, a '.' is not being found in userIP and -1 is being returned.
As a result, Substring fails becaause Substring(0, -1) makes no sense.

Put some validation conditions to ensure there is a valid IP value before doing a sub string.

Posted 2-Dec-14 21:57pm

Abhinav S

Updated 2-Dec-14 21:59pm

v3

Comments

Member 11270220 3-Dec-14 3:59am

so what I do instead of that?

Abhinav S 3-Dec-14 4:00am

Try
int p = userIP.LastIndexOf(".");
if (p >0)
{
userIP = userIP.Substring(0, p);
}

Member 11270220 3-Dec-14 4:03am

now it shows error on that line
serverIP = serverIP.Substring(1, serverIP.LastIndexOf("."));