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How to find and replace href values on links using AngleSharp?

I have a snippet of some HTML that contains some links with hrefs that start with a hashtag like the following
Getting Started
I'm new to AngleSharp and am trying to use it to find these links and replace the hrefs to new values and then return the updated HTML markup back.

The beauty of AngleSharp is that you can essentially fall back to any JS solution - as AngleSharp exposes the W3C DOM API (which is also used by JS). All you'd need to do is replace certain camelCase with PascalCase and use standard .NET tools instead of things from JS.
Let's take for instance How to Change All Links with javascript (sorry, was the first hit on my Google search) and use this as a starting point.
var context = BrowsingContext.New(Configuration.Default);
var document = await context.OpenAsync(res => res.Content(""));
var anchors = document.GetElementsByTagName("a");
for (var i = 0; i < anchors.Length; i++)
{
var anchor = anchors[i] as IHtmlAnchorElement;
anchor.Href = "http://example.com/?redirect=" + anchor.Href;
}
So in our case we are not interested in the same transformation, but quite a similar one. We could do:
for (var i = 0; i < anchors.Length; i++)
{
var anchor = anchors[i] as IHtmlAnchorElement;
if (anchor.GetAttribute("href")?.StartsWith("#") ?? false)
{
anchor.Href = "your-new-value";
}
}
Reason is that Href is always normalized (i.e., a full URL) such that an attribute value of "#foo" may be look like "http://example.com/path#foo". By looking at the raw value we can just assume that the value still starts with the hash symbol.

How can I get a part/subdomain of my URL in C#?

I have a URL like the following
http://yellowcpd.testpace.net
How can I get yellowcpd from this? I know I can do that with string parsing, but is there a builtin way in C#?

Assuming your URLs will always be testpace.net, try this:
var subdomain = Request.Url.Host.Replace("testpace.net", "").TrimEnd('.');
It'll just give you the non-testpace.net part of the Host. If you don't have Request.Url.Host, you can do new Uri(myString).Host instead.

try this
string url = Request.Url.AbsolutePath;
var myvalues= url.Split('.');

How can I get yellowcpd from this? I know I can do that with string
parsing, but is there a builtin way in C#?
.Net doesn't provide a built-in feature to extract specific parts from Uri.Host. You will have to use string manipulation or a regular expression yourself.
The only constant part of the domain string is the TLD. The TLD is the very last bit of the domain string, eg .com, .net, .uk etc. Everything else under that depends on the particular TLD for its position (so you can't assume the next to last part is the "domain name" as, for .co.uk it would be .co

This fits the bill.
Split over two lines:
string rawURL = Request.Url.Host;
string domainName = rawURL .Split(new char[] { '.', '.' })[1];
Or over one:
string rawURL = Request.Url.Host.Split(new char[] { '.', '.' })[1];

The simple answer to your question is no there isn't a built in method to extract JUST the sub-domain. With that said this is the solution that I use...
public enum GetSubDomainOption
{
ExcludeWWW,
IncludeWWW
};
public static class Extentions
{
public static string GetSubDomain(this Uri uri,
GetSubDomainOption getSubDomainOption = GetSubDomainOption.IncludeWWW)
{
var subdomain = new StringBuilder();
for (var i = 0; i < uri.Host.Split(new char[]{'.'}).Length - 2; i++)
{
//Ignore any www values of ExcludeWWW option is set
if(getSubDomainOption == GetSubDomainOption.ExcludeWWW && uri.Host.Split(new char[]{'.'})[i].ToLowerInvariant() == "www") continue;
//I use a ternary operator here...this could easily be converted to an if/else if you are of the ternary operators are evil crowd
subdomain.Append((i < uri.Host.Split(new char[]{'.'}).Length - 3 &&
uri.Host.Split(new char[]{'.'})[i+1].ToLowerInvariant() != "www") ?
uri.Host.Split(new char[]{'.'})[i] + "." :
uri.Host.Split(new char[]{'.'})[i]);
}
return subdomain.ToString();
}
}
USAGE:
var subDomain = Request.Url.GetSubDomain(GetSubDomainOption.ExcludeWWW);
or
var subDomain = Request.Url.GetSubDomain();
I currently have the default set to include the WWW. You could easilly reverse this by switching the optional parameter value in the GetSubDomain() method.
In my opinion this allows for an option that looks nice in code and without digging in appears to be 'built-in' to c#. Just to confirm your expectations...I tested three values and this method will always return just the "yellowcpd" if the exclude flag is used.
www.yellowcpd.testpace.net
yellowcpd.testpace.net
www.yellowcpd.www.testpace.net
One assumption that I use is that...splitting the hostname on a . will always result in the last two values being the domain (i.e. something.com)

As others have pointed out, you can do something like this:
var req = new HttpRequest(filename: "search", url: "http://www.yellowcpd.testpace.net", queryString: "q=alaska");
var host = req.Url.Host;
var yellow = host.Split('.')[1];
The portion of the URL you want is part of the hostname. You may hope to find some method that directly addresses that portion of the name, e.g. "the subdomain (yellowcpd) within TestSpace", but this is probably not possible, because the rules for valid host names allow for any number of labels (see Valid Host Names). The host name can have any number of labels, separated by periods. You will have to add additional restrictions to get what you want, e.g. "Separate the host name into labels, discard www if present and take the next label".

Find/parse server-side <?abc?>-like tags in html document

I guess I need some regex help. I want to find all tags like <?abc?> so that I can replace it with whatever the results are for the code ran inside. I just need help regexing the tag/code string, not parsing the code inside :p.
<b><?abc print 'test' ?></b> would result in <b>test</b>
Edit: Not specifically but in general, matching (<?[chars] (code group) ?>)

This will build up a new copy of the string source, replacing <?abc code?> with the result of process(code)
Regex abcTagRegex = new Regex(#"\<\?abc(?<code>.*?)\?>");
StringBuilder newSource = new StringBuilder();
int curPos = 0;
foreach (Match abcTagMatch in abcTagRegex.Matches(source)) {
string code = abcTagMatch.Groups["code"].Value;
string result = process(code);
newSource.Append(source.Substring(curPos, abcTagMatch.Index));
newSource.Append(result);
curPos = abcTagMatch.Index + abcTagMatch.Length;
}
newSource.Append(source.Substring(curPos));
source = newSource.ToString();
N.B. I've not been able to test this code, so some of the functions may be slightly the wrong name, or there may be some off-by-one errors.

var new Regex(#"<\?(\w+) (\w+) (.+?)\?>")
This will take this source
<b><?abc print 'test' ?></b>
and break it up like this:
Value: <?abc print 'test' ?>
SubMatch: abc
SubMatch: print
SubMatch: 'test'
These can then be sent to a method that can handle it differently depending on what the parts are.
If you need more advanced syntax handling you need to go beyond regex I believe.
I designed a template engine using Antlr but thats way more complex ;)

exp = new Regex(#"<\?abc print'(.+)' \?>");
str = exp.Replace(str, "$1")
Something like this should do the trick. Change the regexes how you see fit

How to prevent entry of HTML into ASP.NET Web form text box

I have several text boxes in an ASP.NET Web Form. I want to ensure that users are not entering HTML into those text boxes. However, I'm not sure how to prevent HTML from being entered. Because of this, I decided that I want to only allow alphanumeric characters, spaces, exclamation point, sharp sign, dollar signs, percentage signs, carets, stars, and left and right parenthesis. I'm omitting the ampersand because I do not want them entering something like "<script&rt;..."
How do I do this? Am I doing it the right way?
Thank you!

Have a look here
http://msdn.microsoft.com/en-us/library/ff649310.aspx
You can put a blanket statement in the web config ValidateRequest = true will check all user input and throw an error if a user inserts something with bad characters.
If you need to allow some html tags then you will need to roll your own.

The page will, by default, prevent users from posting HTML or script in textboxes or textareas. See MSDN

I've used:
HttpUtility.HtmlEncode();
More info here.

You can use a method to clean HTML codes from entry like:
public static string ClearHTML(string Str, Nullable<int> Character)
{
string MetinTxtRegex = Regex.Replace(Str, "<(.|\n)+?>", " ");
string MetinTxtSubStr = string.Empty;
if (Character.HasValue)
{
if (MetinTxtRegex.Length > Character)
{
MetinTxtSubStr = MetinTxtRegex.Substring(0, Character.Value);
MetinTxtSubStr = MetinTxtSubStr.Substring(0, MetinTxtSubStr.LastIndexOf(" ")) + "...";
}
else
{
MetinTxtSubStr = MetinTxtRegex;
}
}
else
{
MetinTxtSubStr = MetinTxtRegex;
}
return MetinTxtSubStr;
}

Adding Control based on info in txt file

Following code, credit: Guffa.
Hello All,
I'm trying to add controls to a Form at runtime based on the information found in a Plain Text File. The structure? of the text file is always the same, and will not change. Example:
File.txt:
Label
"This is a label"
320, 240
Explanation:
Control
Text
Location
The following code, provided to me by Guffa, doesn't cause any errors or anything, but at the same time, nothing happens at all. And I'm not sure why... Can somebody please explain why the label doesn't get created and added to the form with the right info attached to it?
MatchCollection lines = Regex.Matches(File.ReadAllText(fileName), #"(.+?)\r\n""([^""]+)""\r\n(\d+), (\d+)\r\n");
foreach (Match match in lines) {
string control = match.Groups[1].Value;
string text = match.Groups[2].Value;
int x = Int32.Parse(match.Groups[3].Value);
int y = Int32.Parse(match.Groups[4].Value);
Console.WriteLine("{0}, \"{1}\", {2}, {3}", control, text, x, y);
if(control == "Label")
{
Label label = new Label();
label.Text = text;
canvas.Controls.Add(label); // canvas is a Panel Control.
label.Location = new Point(x, y);
}
}
I hope that I have clearly explained my situation. Any help at all would be greatly appreciated.
Thanks for taking the time to read.
jase

My guess is that your file doesn't have quite the right format. If you step into the code, does it match anything?
If so, what gets printed to the console?
Have you tried it with the exact sample shown in the question? While I haven't tried it in a form, I've tried the rest of the code above with the sample file, and it works fine.
Personally I don't think I'd use a regex to match all of the lines like this - it makes it harder to diagnose issues - but it should work okay if the file is correct. You say you don't understand the regex provided - that's another good reason not to use it, to be honest. Even if it's entirely correct, it's not a good idea to use code that you don't understand - you won't be able to maintain it.
I would personally just read the lines three at a time and then deal with them that way. Something like this:
private static readonly Regex LocationPattern = new Regex(#"^(\d+), (\d+)$");
...
using (TextReader reader = File.OpenText(filename))
{
while (true)
{
string control = reader.ReadLine();
string text = reader.ReadLine();
string location = reader.ReadLine();
if (control == null)
{
break;
}
if (text == null || location == null)
{
// Or however you want to handle this...
throw new InvalidConfigurationFileException
("Incorrect number of lines");
}
if (text.Length < 2 || !text.StartsWith("\"") || !text.EndsWith("\""))
{
// Or however you want to handle this...
throw new InvalidConfigurationFileException
("Text is not in quotes");
}
text = text.Substring(1, text.Length - 2);
Match locationMatch = LocationPattern.Match(location);
if (!locationMatch.Success)
{
// Or however you want to handle this...
throw new InvalidConfigurationFileException
("Invalid location: " + location);
}
// You could use int.TryParse if you want to handle this differently
Point parsedLocation = new Point(int.Parse(match.Groups[1].Value),
int.Parse(match.Groups[2].Value));
// Now the rest of the code before
}
}
As you can tell, it's a lot more code - but each part of it is relatively simple. Regular expressions are powerful if you're happy to handle them, but unless something is complicated to express "longhand" I often find it easier to maintain the longer way. Just a personal preference though.

Blind guess: I see the last \r\n in the regex is not optional. Possible that your input file is missing a return character after the last line?
Additional note about sucking at regular expressions: there are some tools that will help you experiment with regular expressions, which might be useful, for example, to understand what's going on in this particular case. I always use Expresso, which among other things analyzes the structure of the regular expression you provide and explains what it does.

Another possibility is that you forgot to add canvas (Panel control) to another control so the chain of controls inside canvas is not displayed and you would maybe not see that the canvas itself doesn't display. Which guess is the best? :-)