I've used both of the following Regular Expressions for testing for a valid email expression with ASP.NET validation controls. I was wondering which is the better expression from a performance standpoint, or if someone has better one.
- \w+([-+.']\w+)*#\w+([-.]\w+)*\.\w+([-.]\w+)*
- ^([0-9a-zA-Z]([-\.\w]*[0-9a-zA-Z])*#([0-9a-zA-Z][-\w]*[0-9a-zA-Z]\.)+[a-zA-Z]{2,9})$
I'm trying avoid the "exponentially slow expression" problem described on the BCL Team Blog.
UPDATE
Based on feedback I ended up creating a function to test if an email is valid:
Public Function IsValidEmail(ByVal emailString As String, Optional ByVal isRequired As Boolean = False) As Boolean
Dim emailSplit As String()
Dim isValid As Boolean = True
Dim localPart As String = String.Empty
Dim domainPart As String = String.Empty
Dim domainSplit As String()
Dim tld As String
If emailString.Length >= 80 Then
isValid = False
ElseIf emailString.Length > 0 And emailString.Length < 6 Then
'Email is too short
isValid = False
ElseIf emailString.Length > 0 Then
'Email is optional, only test value if provided
emailSplit = emailString.Split(CChar("#"))
If emailSplit.Count <> 2 Then
'Only 1 # should exist
isValid = False
Else
localPart = emailSplit(0)
domainPart = emailSplit(1)
End If
If isValid = False OrElse domainPart.Contains(".") = False Then
'Needs at least 1 period after #
isValid = False
Else
'Test Local-Part Length and Characters
If localPart.Length > 64 OrElse ValidateString(localPart, ValidateTests.EmailLocalPartSafeChars) = False OrElse _
localPart.StartsWith(".") OrElse localPart.EndsWith(".") OrElse localPart.Contains("..") Then
isValid = False
End If
'Validate Domain Name Portion of email address
If isValid = False OrElse _
ValidateString(domainPart, ValidateTests.HostNameChars) = False OrElse _
domainPart.StartsWith("-") OrElse domainPart.StartsWith(".") OrElse domainPart.Contains("..") Then
isValid = False
Else
domainSplit = domainPart.Split(CChar("."))
tld = domainSplit(UBound(domainSplit))
' Top Level Domains must be at least two characters
If tld.Length < 2 Then
isValid = False
End If
End If
End If
Else
'If no value is passed review if required
If isRequired = True Then
isValid = False
Else
isValid = True
End If
End If
Return isValid
End Function
Notes:
IsValidEmail is more restrictive about characters allowed then the RFC, but it doesn't test for all possible invalid uses of those characters
If you're wondering why this question is generating so little activity, it's because there are so many other issues that should be dealt with before you start thinking about performance. Foremost among those is whether you should be using regexes to validate email addresses at all--and the consensus is that you should not. It's much trickier than most people expect, and probably pointless anyway.
Another problem is that your two regexes vary hugely in the kinds of strings they can match. For example, the second one is anchored at both ends, but the first isn't; it would match ">>>>foo#bar.com<<<<" because there's something that looks like an email address embedded in it. Maybe the framework forces the regex to match the whole string, but if that's the case, why is the second one anchored?
Another difference is that the first regex uses \w throughout, while the second uses [0-9a-zA-Z] in many places. In most regex flavors, \w matches the underscore in addition to letters and digits, but in some (including .NET) it also matches letters and digits from every writing system known to Unicode.
There are many other differences, but that's academic; neither of those regexes is very good. See here for a good discussion of the topic, and a much better regex.
Getting back to the original question, I don't see a performance problem with either of those regexes. Aside from the nested-quantifiers anti-pattern cited in that BCL blog entry, you should also watch out for situations where two or more adjacent parts of the regex can match the same set of characters--for example,
([A-Za-z]+|\w+)#
There's nothing like that in either of the regexes you posted. Parts that are controlled by quantifiers are always broken up by other parts that aren't quantified. Both regexes will experience some avoidable backtracking, but there are many better reasons than performance to reject them.
EDIT: So the second regex is subject to catastrophic backtracking; I should have tested it thoroughly before shooting my mouth off. Taking a closer look at that regex, I don't see why you need the outer asterisk in the first part:
[0-9a-zA-Z]([-.\w]*[0-9a-zA-Z])*
All that bit does is make sure the first and last characters are alphanumeric while allowing some additional characters in between. This version does the same thing, but it fails much more quickly when no match is possible:
[0-9a-zA-Z][-.\w]*[0-9a-zA-Z]
That would probably suffice to eliminate the backtracking problem, but you could also make the part after the "#" more efficient by using an atomic group:
(?>(?:[0-9a-zA-Z][-\w]*[0-9a-zA-Z]\.)+)[a-zA-Z]{2,9}
In other words, if you've matched all you can of substrings that look like domain components with trailing dots, and the next part doesn't look like a TLD, don't bother backtracking. The first character you would have to give up is the final dot, and you know [a-zA-Z]{2,9} won't match that.
We use this RegEx which has been tested in-house against 1.5 million addresses. It correctly identifies better than 98% of ours, but there are some formats that I'm aware of that it would error on.
^([\w-]+(?:\.[\w-]+)*)#((?:[\w-]+\.)*\w[\w-]{0,66})\.([a-z]{2,6}(?:\.[a-z]{2})?)$
We also make sure that there are no EOL characters in the data since an EOL can fake out this RegEx. Our Function:
Public Function IsValidEmail(ByVal strEmail As String) As Boolean
' Check An eMail Address To Ensure That It Is Valid
Const cValidEmail = "^([\w-]+(?:\.[\w-]+)*)#((?:[\w-]+\.)*\w[\w-]{0,66})\.([a-z]{2,6}(?:\.[a-z]{2})?)$" ' 98% Of All Valid eMail Addresses
IsValidEmail = False
' Take Care Of Blanks, Nulls & EOLs
strEmail = Replace(Replace(Trim$(strEmail & " "), vbCr, ""), vbLf, "")
' Blank eMail Is Invalid
If strEmail = "" Then Exit Function
' RegEx Test The eMail Address
Dim regEx As New System.Text.RegularExpressions.Regex(cValidEmail)
IsValidEmail = regEx.IsMatch(strEmail)
End Function
I am a newbie, but I tried the following and it seemed to have limited the ".xxx" to only two occurrences or less, after the symbol '#'.
^([a-zA-Z0-9]+[a-zA-Z0-9._%-]*#(?:[a-zA-Z0-9-])+(\.+[a-zA-Z]{2,4}){1,2})$
Note: I had to substitute single '\' with double '\\' as I am using this reg expr in R.
These don't check for all allowable email addresses according to the email address RFC.
I let MS to do the work for me:
Public Function IsValidEmail(ByVal emailString As String) As Boolean
Dim retval As Boolean = True
Try
Dim address As New System.Net.Mail.MailAddress(emailString)
Catch ex As Exception
retval = False
End Try
Return retval
End Function
For server side validation, I found Phil Haack's solution to be one of the better ones. His attempt was to stick to the RFC:
string pattern = #"^(?!\.)(""([^""\r\\]|\\[""\r\\])*""|"
+ #"([-a-z0-9!#$%&'*+/=?^_`{|}~]|(?<!\.)\.)*)(?<!\.)"
+ #"#[a-z0-9][\w\.-]*[a-z0-9]\.[a-z][a-z\.]*[a-z]$";
Regex regex = new Regex(pattern, RegexOptions.IgnoreCase);
return regex.IsMatch(emailAddress);
Details:
http://blog.degree.no/2013/01/email-validation-finally-a-net-regular-expression-that-works/
Just to contribute, I am using this regex.
^([a-zA-Z0-9]+[a-zA-Z0-9._%-]*#(?:[a-zA-Z0-9-]+\.)+[a-zA-Z]{2,4})$
The thing about it is the specifications are changing with each domain extension that is introduced.
You sit here mod your regex, test, test, test, and more testing. You finally get what you "think" is accurate then the specification changes... You update your regex to account for what the new requirements are..
Then someone enters aa#aa.aa and you've done all that work for what? It walks through your fancy regex.. bummer!
You may as well just check for a single #, and a "." and move on. I assure you, you will not get someones email if they do not want to give it up. You'll get garbage or their hotmail account they never check and couldn't care less about.
I've seen in many cases this goes horribly wrong and a client calls up because their own email address is rejected because of a poorly crafted regex check. Which as mentioned shouldn't have even been attempted.
TextBox :-
<asp:TextBox ID="txtemail" runat="server" CssClass="form-control pantxt" Placeholder="Enter Email Address"></asp:TextBox>
Required Filed validator:
<asp:RequiredFieldValidator ID="RequiredFieldValidator9" runat="server" ControlToValidate="txtemail" ErrorMessage="Required"></asp:RequiredFieldValidator>
Regular Expression for email validation :
<asp:RegularExpressionValidator ID="validateemail" runat="server" ControlToValidate="txtemail" ValidationExpression="\w+([-+.']\w+)*#\w+([-.]\w+)*\.\w+([-.]\w+)*" ErrorMessage="Invalid Email"></asp:RegularExpressionValidator>
Use this regular expression for email validation in asp.net
Related
i want to allow only alphanumeric password i have written following code to match the same
but the same is not working
Regex.IsMatch(txtpassword.Text, "^[a-zA-Z0-9_]*$") never return false
even if i type password test(which do not contain any number).
ElseIf Regex.IsMatch(txtpassword.Text, "^[a-zA-Z0-9_]*$") = False Then
div_msg.Attributes.Add("class", "err-msg")
lblmsg.Text = "password is incorrect"
I have tried this also
Dim r As New Regex("^[a-zA-Z0-9]+$")
Dim bool As Boolean
bool = r.IsMatch(txtpassword.Text) and for txtpassword.Text = '4444' , bool is coming true i dont know what is wrong.
First of all, the '_' is not a valid alpha-numeric character.
See http://en.wikipedia.org/wiki/Alphanumeric
And, second, take another look at your regular expression.
[a-zA-Z0-9_]*
This can match 0 OR more alpha-numeric characters or 0 OR more '_' characters.
Using this pattern, a password '&#&#^$' would return TRUE.
You probably want to test for 1 OR more characters that ARE NOT an alpha-numeric. If that test returns TRUE, then throw the error.
Hope this helps.
Try the following Expression:
([^a-zA-Z0-9]+)
This will match if your Password contains any character that is not alphanumeric.
If you get a match, do your error handling.
So based on the Regex that you have in the question, it appears you want a password with one lower-case and upper-case letter, one number, and an _; so here is a Regex that will do that:
(?=.*\d)(?=.*[a-z])(?=.*[A-Z])(?=.*_).{4,8}
Debuggex Demo
The {4,8} indicates the length of the password; you can set that accordingly.
I want to convert the below string into classic asp code can any one help
email has some value but it is not going inside the Loop
Can any one help me.
If (IsEmpty(email) And IsNull(email)) Then
EndIf
The code looks like its VBScript already so there is no "conversion" needed, however the code is faulty. Should be:
If IsEmpty(email) Or IsNull(email) Then
End If
a variable cannot both be empty and contain a Null at the same time hence the orginal conditional expression was always false.
You could always try:
If IsEmpty(email) = True Then
'uninitialized
ElseIf IsNull(email) = True Then
'contains null value
ElseIf email = ""
'contains zero length string
Else
'Response.Write email
'MsgBox email
End If
In most cases I try to code so that the variable is guaranteed to be initialized so you don't need to run the IsEmpty check.
Option Explicit
Dim email
email = ""
Why don't you just check the length of the email variable:
If Len(Trim(email)) > 0 Then
Else
YOUR CODE HERE
End If
How can I check if the user has input a null or empty string in classic-asp? Right now I am have this code.
If Request.Form("productId") == "" Then
'my code here
End If
But its not working.
Classic ASP/VBScript uses one = to check for equality, not two. Another thing you may want to try is
If Request.Form("productid") = "" Then
Code here
End If
It is a mess. Here's what I have found ...
(1) To look for existence in the QS, use if IsEmpty(x)=false (ie, URL?x)
(2) To look for a value in the QS, look for if x <> "" (ie, URL?x=anything)
Good luck!
If IsEmpty(Request.Form("inputPhoneNo")) = False Then
response.Write"<script language=javaScript>alert('Blank Phone Number');</script>"
response.Write"<script language=javascript>history.back()</script>"
Else
End If
So I just got my site kicked off the server today and I think this function is the culprit. Can anyone tell me what the problem is? I can't seem to figure it out:
Public Function CleanText(ByVal str As String) As String
'removes HTML tags and other characters that title tags and descriptions don't like
If Not String.IsNullOrEmpty(str) Then
'mini db of extended tags to get rid of
Dim indexChars() As String = {"<a", "<img", "<input type=""hidden"" name=""tax""", "<input type=""hidden"" name=""handling""", "<span", "<p", "<ul", "<div", "<embed", "<object", "<param"}
For i As Integer = 0 To indexChars.GetUpperBound(0) 'loop through indexchars array
Dim indexOfInput As Integer = 0
Do 'get rid of links
indexOfInput = str.IndexOf(indexChars(i)) 'find instance of indexChar
If indexOfInput <> -1 Then
Dim indexNextLeftBracket As Integer = str.IndexOf("<", indexOfInput) + 1
Dim indexRightBracket As Integer = str.IndexOf(">", indexOfInput) + 1
'check to make sure a right bracket hasn't been left off a tag
If indexNextLeftBracket > indexRightBracket Then 'normal case
str = str.Remove(indexOfInput, indexRightBracket - indexOfInput)
Else
'add the right bracket right before the next left bracket, just remove everything
'in the bad tag
str = str.Insert(indexNextLeftBracket - 1, ">")
indexRightBracket = str.IndexOf(">", indexOfInput) + 1
str = str.Remove(indexOfInput, indexRightBracket - indexOfInput)
End If
End If
Loop Until indexOfInput = -1
Next
End If
Return str
End Function
Wouldn't something like this be simpler? (OK, I know it's not identical to posted code):
public string StripHTMLTags(string text)
{
return Regex.Replace(text, #"<(.|\n)*?>", string.Empty);
}
(Conversion to VB.NET should be trivial!)
Note: if you are running this often, there are two performance improvements you can make to the Regex.
One is to use a pre-compiled expression which requires re-writing slightly.
The second is to use a non-capturing form of the regular expression; .NET regular expressions implement the (?:) syntax, which allows for grouping to be done without incurring the performance penalty of captured text being remembered as a backreference. Using this syntax, the above regular expression could be changed to:
#"<(?:.|\n)*?>"
This line is also wrong:
Dim indexNextLeftBracket As Integer = str.IndexOf("<", indexOfInput) + 1
It's guaranteed to always set indexNextLeftBracket equal to indexOfInput, because at this point the character at the position referred to by indexOfInput is already always a '<'. Do this instead:
Dim indexNextLeftBracket As Integer = str.IndexOf("<", indexOfInput+1) + 1
And also add a clause to the if statement to make sure your string is long enough for that expression.
Finally, as others have said this code will be a beast to maintain, if you can get it working at all. Best to look for another solution, like a regex or even just replacing all '<' with <.
In addition to other good answers, you might read up a little on loop invariants a little bit. The pulling out and putting back stuff to the string you check to terminate your loop should set off all manner of alarm bells. :)
Just a guess, but is this like the culprit?
indexOfInput = str.IndexOf(indexChars(i)) 'find instance of indexChar
Per the Microsoft docs, Return Value -
The index position of value if that string is found, or -1 if it is not. If value is Empty, the return value is 0.
So perhaps indexOfInput is being set to 0?
What happens if your code tries to clean the string <a?
As I read it, it finds the indexChar at position 0, but then indexNextLeftBracket and indexRightBracket both equal 0, you fall into the else condition, and then you insert a ">" at position -1, which will presumably insert at the beginning, giving you the string ><a. The new indexRightBracket then becomes 0, so you delete from position 0 for 0 characters, leaving you with ><a. Then the code finds the <a in the code again, and you're off to the races with an infinite memory-consuming loop.
Even if I'm wrong, you need to get yourself some unit tests to reassure yourself that these edge cases work properly. That should also help you find the actual looping code if I'm off-base.
Generally speaking though, even if you fix this particular bug, it's never going to be very robust. Parsing HTML is hard, and HTML blacklists are always going to have holes. For instance, if I really want to get a <input type="hidden" name="tax" tag in, I'll just write it as <input name="tax" type="hidden" and your code will ignore it. Your better bet is to get an actual HTML parser involved, and to only allow the (very small) subset of tags that you actually want. Or even better, use some other form of markup, and strip all HTML tags (again using a real HTML parser of some description).
I'd have to run it through a real compiler but the mindpiler tells me that the str = str.Remove(indexOfInput, indexRightBracket - indexOfInput) line is re-generating an invalid tag such that when you loop through again it finds the same mistake "fixes" it, tries again, finds the mistake "fixes" it, etc.
FWIW heres a snippet of code that removes unwanted HTML tags from a string (It's in C# but the concept translates)
public static string RemoveTags( string html, params string[] allowList )
{
if( html == null ) return null;
Regex regex = new Regex( #"(?<Tag><(?<TagName>[a-z/]+)\S*?[^<]*?>)",
RegexOptions.Compiled |
RegexOptions.IgnoreCase |
RegexOptions.Multiline );
return regex.Replace(
html,
new MatchEvaluator(
new TagMatchEvaluator( allowList ).Replace ) );
}
MatchEvaluator class
private class TagMatchEvaluator
{
private readonly ArrayList _allowed = null;
public TagMatchEvaluator( string[] allowList )
{
_allowed = new ArrayList( allowList );
}
public string Replace( Match match )
{
if( _allowed.Contains( match.Groups[ "TagName" ].Value ) )
return match.Value;
return "";
}
}
That doesn't seem to work for a simplistic <a<a<a case, or even <a>Test</a>. Did you test this at all?
Personally, I hate string parsing like this - so I'm not going to even try figuring out where your error is. It'd require a debugger, and more headache than I'm willing to put in.
I'm pretty sure the answer to this is no. I know that I can write
if lcase(strFoo) = lcase(request.querystring("x")) then...
or use inStr, but I just want to check there isn't some undocumented setting buried in the registry or somewhere that makes the content of VBScript strings behave consistently with the rest of the scripting language!
Thanks
Dan
There is a StrComp function which allows performing a case-insensitive comparison of two strings by passing vbTextCompare as the third argument. The main documentation doesn't make that obvious, but it is discussed in this Hey, Scripting Guy article.
For example:
If StrComp(strFoo, Request.QueryString("x"), vbTextCompare) = 0 Then ...
However, in practice, I use LCase or UCase way more than StrComp for case-insensitive string comparisons because it's more obvious to me.
No. Depending on the function the option may be there (InStr for example) as an optional parameter, but for just straight comparison, there is no global option.
One little known option that can be handy is if you have a list of strings and you want to see if a string is in that list:
Dim dicList : Set dicList = CreateObject("Scripting.Dictionary")
Dim strTest
dicList.CompareMode = 0 ' Binary ie case sensitive
dicList.Add "FOO", ""
dicList.Add "BAR", ""
dicList.Add "Wombat", ""
strTest = "foo"
WScript.Echo CStr(dicList.Exists(strTest))
Set dicList = CreateObject("Scripting.Dictionary")
dicList.CompareMode = 1 ' Text ie case insensitive
dicList.Add "FOO", ""
dicList.Add "BAR", ""
dicList.Add "Wombat", ""
strTest = "foo"
WScript.Echo CStr(dicList.Exists(strTest))
I doubt the existence of such an option since if there were something like that and you use it, you'll lose the ability to compare strings in a case sensitive manner.