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Why does EmailAddressAttribute.IsValid and MailAddress think that emails which contain "ª" are valid? [duplicate]

This question already has answers here:
Can an email address contain international (non-english) characters?
(7 answers)
Closed 1 year ago.
I have this C# code:
void Main()
{
// method 1 - using MailAddress
var email = "fooªbar#cander.com";
Console.WriteLine(IsValidEmail(email));
// method 2 - using EmailAddressAttribute
var validator = new System.ComponentModel.DataAnnotations.EmailAddressAttribute();
Console.WriteLine(validator.IsValid(email));
}
bool IsValidEmail(string email)
{
try
{
var addr = new System.Net.Mail.MailAddress(email);
return addr.Address == email;
}
catch
{
return false;
}
}
That validates the fooªbar#cander.com email address. And... It validates it althougt it has the "ª" symbol. Why? According to: What characters are allowed in an email address? it shoudn't be valid

It validates it althougt it has the "ª" symbol. Why?
Because your Regex allows "one or more \word characters" before the #, and ª is a word character:
RegexStorm uses the .net engine: you can see that the \w pattern (a single word character) has successfully matched an ª (one match)
According to: What characters are allowed in an email address? it shoudn't be valid
Alas, the regular expression you have used does not accurately implement the specification given in the linked question
When it comes to validating email addresses, genuinely I don't think you should try and control it to a very fine degree - it's a headache to form and maintain a complex Regex that considers every variation and it doesn't really bring much benefit, it just generates a pain point for users whose valid emails don't validate because of a bug in your Regex.
When we test for email validity, we basically only check that it contains an #.. what's the worst that can happen if a user types it in wrong?
(apologies if that picture appears huge; it looks reasonable on a cellphone but I recall that iPhone screenshots sometimes end up looking a bit oversized on web)

How do you get an email address within a string

I am pulling many emails from an Exchange 2003 server and from those emails, trying to determine which are bounce-backs (invalid) so I can remove them from our contacts.
What would be the most efficient method of searching the email bodies to find email addresses on the bounce backs?

You might want to look at this page, which has several variants of regexes for matching email addresses and explains the trade-offs for selecting each. You should definitely read it before picking one here.

Just use a regex.
\b[A-Z0-9._%+-]+#[A-Z0-9.-]+\.[A-Z]{2,4}\b

This is the regex that we use in a lot of our applications for email validation;
public static bool CheckEmail(string email)
{
//validate Email
Regex regex = new Regex(#"^([a-zA-Z0-9_\-\.\']+)#((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.)|(([a-zA-Z0-9\-]+\.)+))([a-zA-Z]{2,4}|[0-9]{1,3})$", RegexOptions.IgnoreCase);
Match match = regex.Match(email);
return match.Success;
}
The actual process for correctly identifying a bounced email, rather than an auto-reply or genuine message is a little more complicated, but this will at least give you the email address.

I pulled a few of the answers here into something like this. It actually returns each email address from the string (sometimes there are multiples from the mail host and target address). I can then match each of the email addresses up against the outbound addresses we sent, to verify. I used the article from #plinth to get a better understanding of the regular expression and modified the code from #Chris Bint
However, I'm still wondering if this is the fastest way to monitor 10,000+ emails? Are there any more efficient methods (while still using c#)? The live code won't recreate the Regex object every time within the loop.
public static MatchCollection CheckEmail(string email)
{
Regex regex = new Regex(#"\b[A-Z0-9._%+-]+#[A-Z0-9.-]+\.[A-Z]{2,4}\b", RegexOptions.IgnoreCase);
MatchCollection matches = regex.Matches(email);
return matches;
}

c# regex - matching optionals after a named group

I'm sure this has been quite numerous times but though i've checked all similar questions, i couldn't come up with a solution.
The problem is that i've an input urls similar to;
http://www.justin.tv/peacefuljay
http://www.justin.tv/peacefuljay#/w/778713616/3
http://de.justin.tv/peacefuljay#/w/778713616/3
I want to match the slug part of it (in above examples, it's peacefuljay).
Regex i've tried so far are;
http://.*\.justin\.tv/(?<Slug>.*)(?:#.)?
http://.*\.justin\.tv/(?<Slug>.*)(?:#.)
But i can't come with a solution. Either it fails in the first url or in others.
Help appreciated.

The easiest way of parsing a Uri is by using the Uri class:
string justin = "http://www.justin.tv/peacefuljay#/w/778713616/3";
Uri uri = new Uri(justin);
string s1 = uri.LocalPath; // "/peacefuljay"
string s2 = uri.Segments[1]; // "peacefuljay"
If you insisnt on a regex, you can try someting a bit more specific:
Match mate = Regex.Match(str, #"http://(\w+\.)*justin\.tv(?:/(?<Slug>[^#]*))?");
(\w+\.)* - Ensures you match the domain, not anywhere else in the string (eg, hash or query string).
(?:/(?<Slug>[^#]*))? - Optional group with the string you need. [^#] limits the characters you expect to see in your slug, so it should eliminate the need of the extra group after it.

As I see it there's no reason to treat to the parts after the "slug".
Therefore you only need to match all characters after the host that aren't "/" or "#".
http://.*\.justin\.tv/(?<Slug>[^/#]+)

http://.*\.justin\.tv/(?<Slug>.*)#*?
or
http://.*\.justin\.tv/(?<Slug>.*)(#|$)

C# Extracting a name from a string

I want to extract 'James\, Brown' from the string below but I don't always know what the name will be. The comma is causing me some difficuly so what would you suggest to extract James\, Brown?
OU=James\, Brown,OU=Test,DC=Internal,DC=Net
Thanks

A regex is likely your best approach
static string ParseName(string arg) {
var regex = new Regex(#"^OU=([a-zA-Z\\]+\,\s+[a-zA-Z\\]+)\,.*$");
var match = regex.Match(arg);
return match.Groups[1].Value;
}

You can use a regex:
string input = #"OU=James\, Brown,OU=Test,DC=Internal,DC=Net";
Match m = Regex.Match(input, "^OU=(.*?),OU=.*$");
Console.WriteLine(m.Groups[1].Value);

A quite brittle way to do this might be...
string name = #"OU=James\, Brown,OU=Test,DC=Internal,DC=Net";
string[] splitUp = name.Split("=".ToCharArray(),3);
string namePart = splitUp[1].Replace(",OU","");
Console.WriteLine(namePart);
I wouldn't necessarily advocate this method, but I've just come back from a departmental Christmas lyunch and my brain is not fully engaged yet.

I'd start off with a regex to split up the groups:
Regex rx = new Regex(#"(?<!\\),");
String test = "OU=James\\, Brown,OU=Test,DC=Internal,DC=Net";
String[] segments = rx.Split(test);
But from there I would split up the parameters in the array by splitting them up manually, so that you don't have to use a regex that depends on more than the separator character used. Since this looks like an LDAP query, it might not matter if you always look at params[0], but there is a chance that the name might be set as "CN=". You can cover both cases by just reading the query like this:
String name = segments[0].Split('=', 2)[1];

That looks suspiciously like an LDAP or Active Directory distinguished name formatted according to RFC 2253/4514.
Unless you're working with well known names and/or are okay with a fragile hackaround (like the regex solutions) - then you should start by reading the spec.
If you, like me, generally hate implementing code according to RFCs - then hope this guy did a better job following the spec than you would. At least he claims to be 2253 compliant.

If the slash is always there, I would look at potentially using RegEx to do the match, you can use a match group for the last and first names.
^OU=([a-zA-Z])\,\s([a-zA-Z])
That RegEx will match names that include characters only, you will need to refine it a bit for better matching for the non-standard names. Here is a RegEx tester to help you along the way if you go this route.

Replace \, with your own preferred magic string (perhaps & #44;), split on remaining commas or search til the first comma, then replace your magic string with a single comma.
i.e. Something like:
string originalStr = #"OU=James\, Brown,OU=Test,DC=Internal,DC=Net";
string replacedStr = originalStr.Replace("\,", ",");
string name = replacedStr.Substring(0, replacedStr.IndexOf(","));
Console.WriteLine(name.Replace(",", ","));

Assuming you're running in Windows, use PInvoke with DsUnquoteRdnValueW. For code, see my answer to another question: https://stackoverflow.com/a/11091804/628981

If the format is always the same:
string line = GetStringFromWherever();
int start = line.IndexOf("=") + 1;//+1 to get start of name
int end = line.IndexOf("OU=",start) -1; //-1 to remove comma
string name = line.Substring(start, end - start);
Forgive if syntax is not quite right - from memory. Obviously this is not very robust and fails if the format ever changes.

IP address parsing in .NET

I'm using IPAddress.TryParse() to parse IP addresses. However, it's a little too permissive (parsing "1" returns 0.0.0.1). I'd like to limit the input to dotted octet notation. What's the best way to do this?
(Note: I'm using .NET 2.0)
Edit
Let me clarify:
I'm writing an app that will scan a range of IPs looking for certain devices (basically a port scanner). When the user enters "192.168.0.1" for the starting address, I want to automatically fill in "192.168.0.255" as the ending address. The problem is that when they type "1", it parses as "0.0.0.1" and the ending address fills in as "0.0.0.255" - which looks goofy.

If you are interested in parsing the format, then I'd use a regular expression. Here's a good one (source):
bool IsDottedDecimalIP(string possibleIP)
{
Regex R = New Regex(#"\b(?:\d{1,3}\.){3}\d{1,3}\b");
return R.IsMatch(possibleIP) && Net.IPAddress.TryParse(possibleIP, null);
}
That regex doesn't catch invalid IPs but does enforce your pattern. The TryParse checks their validity.

An IP address is actually a 32 bit number - it is not xxx.xxx.xxx.xxx - that's just a human readable format for the same. So IP address 1 is actually 0.0.0.1.
EDIT: Given the clarification, you could either go with a regex as has been suggested, or you could format the short cuts to your liking, so if you want "1" to appears as "1.0.0.0". you could append that and still use the parse method.