Develop Reference

Parameters with + sign within the custom URL

I'm trying to reference an image like this:
<img src="/controller/method/#Model.attribute">
This works until the attribute has a plus sign. I already know that the + sign has a semantic meaning but I'd like to keep it, because some values have the plus sign.
I've tried:
<img src="/controller/method/#HttpUtility.HtmlEncode(#Model.attribute)">
And on the server side:
public method(string param)
{
string p = HttpUtility.HtmlDecode(param);
}
How can I accomplish this using ASP.NET MVC 5?

You need to use UrlEncode:
<img src="/controller/method/#HttpUtility.UrlEncode(Model.attribute)">
And do nothing in the method:
public ActionResult method(string param){
// param should already be decoded
}

Did some testing and got error page while trying to reproduce scenario you described.
Here is related question: double escape sequence inside a url : The request filtering module is configured to deny a request that contains a double escape sequence

In my designs, I'm avoiding any direct use of model fields as part of the URL. It's not only the question of URL-encoding them - which you can always do - but also the question of readability.
What I do instead is to add another field to the model, which is the URL-ready representation of an attribute. That field can be calculated from the original field by only accepting letters and numbers and replacing spaces or any other character with a dash.
For example, if you had the attribute set to someone's pencil + one, the auto-created URL version of this attribute would be someone-s-pencil-one.
You can customize this process, make it recognize some domain-specific words, etc. But that is the general idea I'm always following in my designs.
As a quick solution you can use a regular expression to isolate acceptable words and then separate them with dashes for better readability:
string encoded = string.Join("-",
Regex.Matches(attributeValue, #"[a-zA-z0-9]+")
.Cast<Match>()
.Select(match => match.Value)
.ToArray());
When done this way, you must account for possible duplicates. Part of the information is lost with this encoding.
If you fear that two models could clash with the same URL, then you have to do something to break the clash. Some websites append a GUID to the generated URL to make it unique.
Another possibility is to generate a short random string, like 3-5 letters only, and store it in the database so that you can control its uniqueness. Everything in this solution is subordinated to readability, keep that in mind.

RegEx to Validate URL with optional Scheme

I want to validate a URL using regular expression. Following are my conditions to validate the URL:
Scheme is optional
Subdomains should be allowed
Port number should be allowed
Path should be allowed.
I was trying the following pattern:
((http|https)://)?([\w-]+\.)+[\w-]+(/[\w- ./?%&=]*)?
But I am not getting the desired results. Even an invalid URL like '*.example.com' is getting matched.
What is wrong with it?

are you matching the entire string? you don't say what language you are using, but in python it looks like you may be using search instead of match.
one way to fix this is to start you regexp with ^ and end it with $.

While parsing URL's is best left to a library (since I know perl best, I would suggest something like http://search.cpan.org/dist/URI/), if you want some help debugging that statement, it might be best to try it in a debugger, something like: http://www.debuggex.com/.
I think one of the main reasons it is matching, is because you don't use beginning and ending string match markers. Meaning, no part of that string might be matching what you put in explicitly, but because you haven't marked it with beginning and end markers for the string, your regex could just be matching 'example.com' in your string, not the entire input.

Found the regular expression for my condition with help from your inputs
^(http(s)?://)?[0-9a-zA-Z]([-.\w]*[0-9a-zA-Z])*(:(0-9)*)*(\/?)([a-zA-Z0-9\-‌​\.\?\,\'\/\\\+&%\$#_]*)?$

Following code works for me in c#
private static bool IsValidUrl(string url)
{
return new Regex(#"^(http|http(s)?://)?([\w-]+\.)+[\w-]+[.\w]+(\[\?%&=]*)?").IsMatch(url) &&!new Regex(#"[^a-zA-Z0-9]+$").IsMatch(url);
}
it allows "something.anything (at least 2 later after period) with or without http(s) and www.

how to replace the exact word by another in a list?

I have a list like :
george fg
michel fgu
yasser fguh
I would like to replace fg, fgu, and fguh by "fguhCool" I already tried something like this :
foreach (var ignore in NameToPoulate)
{
tempo = ignore.Replace("fg", "fguhCool");
NameToPoulate_t.Add(tempo);
}
But then "fgu" become "fguhCoolu" and "fguh" become "fguhCooluh" is there are a better idea ?
Thanks for your help.

I assume that this is a homework assignment and that you are being tested for the specific algorihm rather than any code that does the job.
This is probably what your teacher has in mind:
Students will realize that the code should check for "fguh" first, then "fgu" then "fg". The order is important because replacing "fg" will, as you have noticed, destroy a "fguh".
This will by some students be implemented as a loop with if-else conditions in them. So that you will not replace a "fg" that is within an already replaced "fguhCool".
But then you will find that the algorithm breaks down if "fg" and "fgu" are both within the same string. You cannot then allow the presence of "fgu" prevent you to check for "fg" at a different part of the string.
The answer that your teacher is looking for is probably that you should first locate "fguh", "fgu" and "fg" (in that order) and replace them with an intermediary string that doesn't contain "fg". Then after you have done that, you can search for that intermediary string and replace it with "fguhCool".

You could use regular expressions:
Regex.Replace(#"\bfg\b", "fguhCool");
The \b matches a so-called word boundary which means it matches the beginnnig or end of a word (roughly, but for this purpose enough).

Use a regular expression:
Regex.Replace("fg(uh?)?", "fguhCool");
An alternative would be replacing the long words for the short ones first, then replacing the short for the end value (I'm assuming all words - "fg", "fgu" and "fguh" - would map to the same value "fguhCool", right?)
tempo = ignore
.Replace("fguh", "fg")
.Replace("fgu", "fg")
.Replace("fg", "fguhCool");
Obs.: That assumes those words can appear anywhere in the string. If you're worried about whole words (i.e. cases where those words are not substrings of a bigger word), then see #Joey's answer (in this case, simple substitutions won't do, regexes are really the best option).

What's the best way to parse a string for "bad" words in C#?

I'm thinking of something like:
foreach (var word in paragraph.split(' ')) {
if (badWordArray.Contains(word) {
// do something about it
}
}
but I'm sure there's a better way.
Thanks in advance!
UPDATE
I'm not looking to remove obscenities automatically... for my web app, I want to be notified if a word I deem "bad" is used. Then I'll review it myself to make sure it's legit. An auto flagging system of sorts.

While your way works, it may be a bit time consuming. There is a wonderful response here for a previous SO question. Though the question talks about PHP instead of C#, I think it can be easily ported.
Edit to add sample code:
public string FilterWords(string inputWords) {
Regex wordFilter = new Regex("(puppies|kittens|dolphins|crabs)");
return wordFilter.Replace(inputWords, "<3");
}
That should work for you, more or less.
Edit to answer OP clarification:
I'm not looking to remove obscenities automatically... for my web app, I want to be notified if a word I deem "bad" is used.
Much as the replacement portion above, you can see if something matches like so:
public bool HasBadWords(string inputWords) {
Regex wordFilter = new Regex("(puppies|kittens|dolphins|crabs)");
return wordFilter.IsMatch(inputWords);
}
It will return true if the string you passed to it contains any words in the list.

At my job we put some automatic bad word filtering into our software (it's kind of shocking to be browsing the source and suddenly run across the array containing several pages of obscenity).
One tip is to pre-process the user input before testing against your list, in that case that someone is trying to sneak something by you. So by way of preprocessing, we
uppercase everything in the input
remove most non-alphanumerics (that is, just splice out any spaces, or punctuation, etc.)
and then assuming someone is trying to pass off digits for letters, do the something like this: replace zero with O, 9 with G, 5 with S, etc. (get creative)
And then get some friends to try to break it. It's fun.

You could consider using the HashKey objects or Dictionary<T1, T2> instead of the array as using a Dictionary for example can make code more efficient, because the .Contains() method becomes .Keys.Contains() which is way more efficient. This is especially true if you have a large list of profanities (not sure how many there are! :)

How to split a user-generated string which may contain the delimitter?

I'd like to String.Split() the following string using a comma as the delimitter:
John,Smith,123 Main Street,212-555-1212
The above content is entered by a user. If they enter a comma in their address, the resulting string would cause problems to String.Split() since you now have 5 fields instead of 4:
John,Smith,123 Main Street, Apt 101,212-555-1212
I can use String.Replace() on all user input to replace commas with something else, and then use String.Replace() again to convert things back to commas:
value = value.Replace(",", "*");
However, this can still be fooled if a user happens to use the placeholder delimitter "*" in their input. Then you'd end up with extra commas and no asterisks in the result.
I see solutions online for dealing with escaped delimitters, but I haven't found a solution for this seemingly common situation. What am I missing?
EDIT: This is called delimitter collision.

This is a common scenario — you have some arbitrary string values that you would like to compose into a structure, which is itself a string, but without allowing the values to interfere with the delimiters in structure around them.
You have several options:
Input restriction: If it is acceptable for your scenario, the simplest solution is to restrict the use of delimiters in the values. In your specific case, this means disallow commas.
Encoding: If input restriction is not appropriate, the next easiest option would be to encode the entire input value. Choose an encoding that does not have delimiters in its range of possible outputs (e.g. Base64 does not feature commas in its encoded output)
Escaping delimiters: A slightly more complex option is to come up with a convention for escaping delimiters. If you're working with something mainstream like CSV it is likely that the problem of escaping is already solved, and there's a standard library that you can use. If not, then it will take some thought to come up with a complete escaping system, and implement it.
If you have the flexibility to not use CSV for your data representation this would open up a host of other options. (e.g. Consider the way in which parameterised SQL queries sidestep the complexity of input escaping by storing the parameter values separately from the query string.)

This may not be an option for you but would is it not be easier to use a very uncommon character, say a pipe |, as your delimiter and not allow this character to be entered in the first instance?

If this is CSV, the address should be surrounded by quotes. CSV parsers are widely available that take this into account when parsing the text.
John,Smith,"123 Main Street, Apt. 6",212-555-1212

One foolproof solution would be to convert the user input to base64 and then delimit with a comma. It will mean that you will have to convert back after parsing.

You could try putting quotes, or some other begin and end delimiters, around each of the user inputs, and ignore any special character between a set of quotes.
This really comes down to a situation of cleansing user inputs. You should only allow desired characters in the user input and reject/strip invalid inputs from the user. This way you could use your asterisk delimiter.
The best solution is to define valid characters, and reject non valid characters somehow, then use the nonvalid character (which will not appear in the input since they are "banned") as you delimiters

Dont allow the user to enter that character which you are using as a Delimiter. I personally feel this is best way.

Funny solution (works if the address is the only field with coma):
Split the string by coma. First two pieces will be name and last name; the last piece is the telephone - take those away. Combine the rest by coma back - that would be address ;)

In a sense, the user is already "escaping" the comma with the space afterward.
So, try this:
string[] values = RegEx.Split(value, ",(?![ ])");
The user can still break this if they don't put a space, and there is a more foolproof method (using the standard CSV method of quoting values that contain commas), but this will do the trick for the use case you've presented.
One more solution: provide an "Address 2" field, which is where things like apartment numbers would traditionally go. User can still break it if they are lazy, though what they'll actually break the fields after address2.

Politely remind your users that properly-formed street addresses in the United States and Canada should NEVER contain any punctuation whatsoever, perhaps?
The process of automatically converting corrupted data into useful data is non-trivial without heuristic logic. You could try to outsource the parsing by calling a third-party address-formatting library to apply the USPS formatting rules.
Even USPS requires the user to perform much of the work, by having components of the address entered into distinct fields on their address "canonicalizer" page (http://zip4.usps.com/zip4/welcome.jsp).