Develop Reference

How to decode HTML into string?

I need to decode HTML into plain text. I know that there are a lot of questions like this but I noticed one problem with those solutions and don't know how to solve it.
For example we have this piece of HTML:
<h1><strong>Some text</strong></h1><p><br></p><p>Some more text</p>
Tried regex solutions, HttpUtility.HtmlDecode method. And all of them give this output: Some textSome more text. Words get connected where they should be separate. Is there a way to decode string without merging words?

It's not clear what separator you wan between things that were not separated in the first place. So I used NewLine \n.
Where(x=>!string.IsNullOrWhiteSpace(x) will remove the empty element that will result in a lot of \n\n in more complex html doc
var input = "<h1><strong>Some text</strong></h1><p><br></p><p>Some more text</p>";
var htmlDocument = new HtmlDocument();
htmlDocument.LoadHtml(input);
var result = string.Join(
"\n",
htmlDocument
.DocumentNode
.ChildNodes
.Select(x=> x.InnerText)
.Where(x=>!string.IsNullOrWhiteSpace(x))
);
Result:
"Some text\nSome more text"

easy way to do it is to use HTML Agility pack:
HtmlDocument htmlDocument= new HtmlDocument();
htmlDocument.Load(htmlString);
string res=htmlDocument.DocumentNode.SelectSingleNode("YOUR XPATH TO THE INTRESTING ELEMENT").InnerText

You can use something as follows. In this sample i have used new line to separate inner text, hope you can adapt this to suite your scenario.
public static string GetPlainTextFromHTML(string inputText)
{
// Extracted plain text
var plainText = string.Empty;
if(string.IsNullOrWhiteSpace(inputText))
{
return plainText;
}
var htmlNote = new HtmlDocument();
htmlNote.LoadHtml(inputText);
var nodes = htmlNote.DocumentNode.ChildNodes;
if(nodes == null)
{
return plainText;
}
StringBuilder innerString = new StringBuilder();
// Replace <p> with new lines
foreach (HtmlNode node in nodes)
{
innerString.Append(node.InnerText);
innerString.Append("\\n");
}
plainText = innerString.ToString();
return plainText;
}

You can use a regex : <(div|/div|br|p|/p)[^>]{0,}>

How to extract an url from a String in C#

I have this string :
"<figure><img
src='http://myphotos.net/image.ashx?type=2&image=Images\\2\\9\\11\\12\\3\\8\\4\\7\\685621455625.jpg'
href='JavaScript:void(0);' onclick='return takeImg(this)'
tabindex='1' class='myclass' width='55' height='66' alt=\"myalt\"></figure>"
How can I retrieve this link :
http://myphotos.net/image.ashx?type=2&image=Images\\2\\9\\11\\12\\3\\8\\4\\7\\685621455625.jpg
All string are the same type so somehow I need to get substring between src= and href. But I don't know how to do that. Thanks.

If you parse HTML don't not use string methods but a real HTML parser like HtmlAgilityPack:
var doc = new HtmlAgilityPack.HtmlDocument();
doc.LoadHtml(html); // html is your string
var linksAndImages = doc.DocumentNode.SelectNodes("//a/#href | //img/#src");
var allSrcList = linksAndImages
.Select(node => node.GetAttributeValue("src", "[src not found]"))
.ToList();

You can use regex:
var src = Regex.Match("the string", "<img.+?src=[\"'](.+?)[\"'].*?>", RegexOptions.IgnoreCase).Groups[1].Value;

In general, you should use an HTML/XML parser when parsing a value from HTML code, but with a limited string like this, Regex would be fine.
string url = Regex.Match(htmlString, #"src='(.*?)'").Groups[1].Value;

If your string is always in same format, you can easily do this like so :
string input = "<figure><img src='http://myphotos.net/image.ashx?type=2&image=Images\\2\\9\\11\\12\\3\\8\\4\\7\\685621455625.jpg' href='JavaScript:void(0);' onclick='return takeImg(this)' tabindex='1' class='myclass' width='55' height='66' alt=\"myalt\"></figure>";
// link is between ' signs starting from the first ' sign so you can do :
input = input.Substring(input.IndexOf("'")).Substring(input.IndexOf("'"));
// now your string looks like : "http://myphotos.net/image.ashx?type=2&image=Images\\2\\9\\11\\12\\3\\8\\4\\7\\685621455625.jpg"
return input;

string str = "<figure><imgsrc = 'http://myphotos.net/image.ashx?type=2&image=Images\\2\\9\\11\\12\\3\\8\\4\\7\\685621455625.jpg'href = 'JavaScript:void(0);' onclick = 'return takeImg(this)'tabindex = '1' class='myclass' width='55' height='66' alt=\"myalt\"></figure>";
int pFrom = str.IndexOf("src = '") + "src = '".Length;
int pTo = str.LastIndexOf("'href");
string url = str.Substring(pFrom, pTo - pFrom);
Source :
Get string between two strings in a string

Q is your string in this case, i look for the index of the attribute you want (src = ') then I remove the first few characters (7 including spaces) and after that you look for when the text ends by looking for '.
With removing the first few characters you could use .IndexOf to look for how many to delete so its not hard coded.
string q =
"<figure><img src = 'http://myphotos.net/image.ashx?type=2&image=Images\\2\\9\\11\\12\\3\\8\\4\\7\\685621455625.jpg' href = 'JavaScript:void(0);' onclick = 'return takeImg(this)'" +
"tabindex = '1' class='myclass' width='55' height='66' alt=\"myalt\"></figure>";
string z = q.Substring(q.IndexOf("src = '"));
z = z.Substring(7);
z = z.Substring(0, z.IndexOf("'"));
MessageBox.Show(z);
This is certainly not the most elegant way (look at the other answers for that :)).

Find & Replace Multiple Instagram Urls In A String Using C#

I want to find all the instagram urls within a string, and replace them with the embed url.
But I'm keen on performance, as this could be 5 to 20 posts each anything up to 6000 characters with an unknown amount of instagram urls in which need converting.
Url examples (Could be any of these in each string, so would need to match all)
http://instagram.com/p/xPnQ1ZIY2W/?modal=true
http://instagram.com/p/xPnQ1ZIY2W/
http://instagr.am/p/xPnQ1ZIY2W/
And this is what I need to replace them with (An embedded version)
<img src="http://instagram.com/p/xPnQ1ZIY2W/media/?size=l" class="instagramimage" />
I was thinking about going for regex? But is this the quickest and most performant way of doing this?
Any examples greatly appreciated.

Something like:
Regex reg = new Regex(#"http://instagr\.?am(?:\.com)?/\S*");
Edited regex. However i would combine this with a stringreader and do it line by line. Then put the string (modified or not) into a stringbuilder:
string original = #"someotherText http://instagram.com/p/xPnQ1ZIY2W/?modal=true some other text
some other text http://instagram.com/p/xPnQ1ZIY2W/ some other text
some other text http://instagr.am/p/xPnQ1ZIY2W/ some other text";
StringBuilder result = new StringBuilder();
using (StringReader reader = new StringReader(original))
{
while (reader.Peek() > 0)
{
string line = reader.ReadLine();
if (reg.IsMatch(line))
{
string url = reg.Match(line).ToString();
result.AppendLine(reg.Replace(line,string.Format("<img src=\"{0}\" class=\"instagramimage\" />",url)));
}
else
{
result.AppendLine(line);
}
}
}
Console.WriteLine(result.ToString());
You mean like this?
class Program
{
private static Regex reg = new Regex(#"http://instagr\.?am(?:\.com)?/\S*", RegexOptions.Compiled);
private static Regex idRegex = new Regex(#"(?<=p/).*?(?=/)",RegexOptions.Compiled);
static void Main(string[] args)
{
string original = #"someotherText http://instagram.com/p/xPnQ1ZIY2W/?modal=true some other text
some other text http://instagram.com/p/xPnQ1ZIY2W/ some other text
some other text http://instagr.am/p/xPnQ1ZIY2W/ some other text";
StringBuilder result = new StringBuilder();
using (StringReader reader = new StringReader(original))
{
while (reader.Peek() > 0)
{
string line = reader.ReadLine();
if (reg.IsMatch(line))
{
string url = reg.Match(line).ToString();
result.AppendLine(reg.Replace(line, string.Format("<img src=\"http://instagram.com/p/{0}/media/?size=1\" class=\"instagramimage\" />", idRegex.Match(url).ToString())));
}
else
{
result.AppendLine(line);
}
}
}
Console.WriteLine(result.ToString());
}
}

A well-crafted and compiled regular expression is hard to beat, especially since you're doing replacements, not just searching, but you should test to be sure.
If the Instagram URLs are only within HTML attributes, here's my first stab at a pattern to look for:
(?<=")(https?://instagr[^">]+)
(I added a check for https as well, which you didn't mention but I believe is supported by Instagram.)
Some false positives are theoretically possible, but it will perform better than pedantically matching every legal variation of an Instagram URL. (The ">" check is just in case the HTML is missing the end quote for some reason.)

is it possible to fix the problem in HtmlAgilityPack when there is a not closed html tag?

well i have the following problem.
the html i have is malformed and i have problems with selecting nodes using html agility pack when this is the case.
the code is below:
string strHtml = #"
<html>
<div>
<p><strong>Elem_A</strong>String_A1_2 String_A1_2</p>
<p><strong>Elem_B</strong>String_B1_2 String_B1_2</p>
</div>
<div>
<p><strong>Elem_A</strong>String_A2_2 <String_A2_2> asdas</p>
<p><strong>Elem_B</strong>String_B2_2 String_B2_2</p>
</div>
</html>";
HtmlAgilityPack.HtmlDocument objHtmlDocument = new HtmlAgilityPack.HtmlDocument();
objHtmlDocument.LoadHtml(strHtml);
HtmlAgilityPack.HtmlNodeCollection colnodePs = objHtmlDocument.DocumentNode.SelectNodes("//p");
List<string> lststrText = new List<string>();
foreach (HtmlAgilityPack.HtmlNode nodeP in colnodePs)
{
lststrText.Add(nodeP.InnerHtml);
}
the problem is that String_A2_2 is enclosed in brackets.
so htmlagility pack returns 5 strings instead of 4 in the lststrText.
so is it possible to let htmlagility pack return element 3 as
"<strong>Elem_A</strong>String_A2_2 <String_A2_2> asdas"?
or maybe i can do some preprocessing to close the element?
the current content of lststrText is
lststrText[0] = "<strong>Elem_A</strong>String_A1_2 String_A1_2"
lststrText[1] = "<strong>Elem_B</strong>String_B1_2 String_B1_2"
lststrText[2] = ""
lststrText[3] = ""
lststrText[4] = "<strong>Elem_B</strong>String_B2_2 String_B2_2"

Most html parsers try to build a working DOM, meaning dangling tags are not accepted. They will be converted, or closed in some way.
If only selecting the nodes is of importance to you, and speed and huge amounts of data is not an issue, you could grab all your <p> tags with a regular expression instead:
Regex reMatchP = new Regex(#"<(p)>.*?</\1>");
foreach (Match m in reMatchP.Matches(strHtml))
{
Console.WriteLine(m.Value);
}
This regular expression assumes the <p> tags are well formed and closed.
If you are to run this Regex a lot in your program you should declare it as:
static Regex reMatchP = new Regex(#"<(p)>.*?</\1>", RegexOptions.Compiled);
[Edit: Agility pack change]
If you want to use HtmlAgility pack you can modify the PushNodeEnd function in HtmlDocument.cs:
if (HtmlNode.IsCDataElement(CurrentNodeName()))
{
_state = ParseState.PcData;
return true;
}
// new code start
if ( !AllowedTags.Contains(_currentnode.Name) )
{
close = true;
}
// new code end
where AllowedTags would be a list of all known tags: b, p, br, span, div, etc.
the output is not 100% what you want, but maybe close enough?
<strong>Elem_A</strong>String_A1_2 String_A1_2
<strong>Elem_B</strong>String_B1_2 String_B1_2
<strong>Elem_A</strong>String_A2_2 <ignorestring_a2_2></ignorestring_a2_2> asdas
<strong>Elem_B</strong>String_B2_2 String_B2_2

You could use TidyNet to do the pre/postprocessing you allude to. Can you edit your answer to explain why that wouldnt be applicable in your case?

How can I strip HTML tags from a string in ASP.NET?

Using ASP.NET, how can I strip the HTML tags from a given string reliably (i.e. not using regex)? I am looking for something like PHP's strip_tags.
Example:
<ul><li>Hello</li></ul>
Output:
"Hello"
I am trying not to reinvent the wheel, but I have not found anything that meets my needs so far.

If it is just stripping all HTML tags from a string, this works reliably with regex as well. Replace:
<[^>]*(>|$)
with the empty string, globally. Don't forget to normalize the string afterwards, replacing:
[\s\r\n]+
with a single space, and trimming the result. Optionally replace any HTML character entities back to the actual characters.
Note:
There is a limitation: HTML and XML allow > in attribute values. This solution will return broken markup when encountering such values.
The solution is technically safe, as in: The result will never contain anything that could be used to do cross site scripting or to break a page layout. It is just not very clean.
As with all things HTML and regex:
Use a proper parser if you must get it right under all circumstances.

Go download HTMLAgilityPack, now! ;) Download LInk
This allows you to load and parse HTML. Then you can navigate the DOM and extract the inner values of all attributes. Seriously, it will take you about 10 lines of code at the maximum. It is one of the greatest free .net libraries out there.
Here is a sample:
string htmlContents = new System.IO.StreamReader(resultsStream,Encoding.UTF8,true).ReadToEnd();
HtmlAgilityPack.HtmlDocument doc = new HtmlAgilityPack.HtmlDocument();
doc.LoadHtml(htmlContents);
if (doc == null) return null;
string output = "";
foreach (var node in doc.DocumentNode.ChildNodes)
{
output += node.InnerText;
}

Regex.Replace(htmlText, "<.*?>", string.Empty);

protected string StripHtml(string Txt)
{
return Regex.Replace(Txt, "<(.|\\n)*?>", string.Empty);
}
Protected Function StripHtml(Txt as String) as String
Return Regex.Replace(Txt, "<(.|\n)*?>", String.Empty)
End Function

I've posted this on the asp.net forums, and it still seems to be one of the easiest solutions out there. I won't guarantee it's the fastest or most efficient, but it's pretty reliable.
In .NET you can use the HTML Web Control objects themselves. All you really need to do is insert your string into a temporary HTML object such as a DIV, then use the built-in 'InnerText' to grab all text that is not contained within tags. See below for a simple C# example:
System.Web.UI.HtmlControls.HtmlGenericControl htmlDiv = new System.Web.UI.HtmlControls.HtmlGenericControl("div");
htmlDiv.InnerHtml = htmlString;
String plainText = htmlDiv.InnerText;

I have written a pretty fast method in c# which beats the hell out of the Regex. It is hosted in an article on CodeProject.
Its advantages are, among better performance the ability to replace named and numbered HTML entities (those like & and &203;) and comment blocks replacement and more.
Please read the related article on CodeProject.
Thank you.

For those of you who can't use the HtmlAgilityPack, .NETs XML reader is an option. This can fail on well formatted HTML though so always add a catch with regx as a backup. Note this is NOT fast, but it does provide a nice opportunity for old school step through debugging.
public static string RemoveHTMLTags(string content)
{
var cleaned = string.Empty;
try
{
StringBuilder textOnly = new StringBuilder();
using (var reader = XmlNodeReader.Create(new System.IO.StringReader("<xml>" + content + "</xml>")))
{
while (reader.Read())
{
if (reader.NodeType == XmlNodeType.Text)
textOnly.Append(reader.ReadContentAsString());
}
}
cleaned = textOnly.ToString();
}
catch
{
//A tag is probably not closed. fallback to regex string clean.
string textOnly = string.Empty;
Regex tagRemove = new Regex(#"<[^>]*(>|$)");
Regex compressSpaces = new Regex(#"[\s\r\n]+");
textOnly = tagRemove.Replace(content, string.Empty);
textOnly = compressSpaces.Replace(textOnly, " ");
cleaned = textOnly;
}
return cleaned;
}

string result = Regex.Replace(anytext, #"<(.|\n)*?>", string.Empty);

I've looked at the Regex based solutions suggested here, and they don't fill me with any confidence except in the most trivial cases. An angle bracket in an attribute is all it would take to break, let alone mal-formmed HTML from the wild. And what about entities like &? If you want to convert HTML into plain text, you need to decode entities too.
So I propose the method below.
Using HtmlAgilityPack, this extension method efficiently strips all HTML tags from an html fragment. Also decodes HTML entities like &. Returns just the inner text items, with a new line between each text item.
public static string RemoveHtmlTags(this string html)
{
if (String.IsNullOrEmpty(html))
return html;
var doc = new HtmlAgilityPack.HtmlDocument();
doc.LoadHtml(html);
if (doc.DocumentNode == null || doc.DocumentNode.ChildNodes == null)
{
return WebUtility.HtmlDecode(html);
}
var sb = new StringBuilder();
var i = 0;
foreach (var node in doc.DocumentNode.ChildNodes)
{
var text = node.InnerText.SafeTrim();
if (!String.IsNullOrEmpty(text))
{
sb.Append(text);
if (i < doc.DocumentNode.ChildNodes.Count - 1)
{
sb.Append(Environment.NewLine);
}
}
i++;
}
var result = sb.ToString();
return WebUtility.HtmlDecode(result);
}
public static string SafeTrim(this string str)
{
if (str == null)
return null;
return str.Trim();
}
If you are really serious, you'd want to ignore the contents of certain HTML tags too (<script>, <style>, <svg>, <head>, <object> come to mind!) because they probably don't contain readable content in the sense we are after. What you do there will depend on your circumstances and how far you want to go, but using HtmlAgilityPack it would be pretty trivial to whitelist or blacklist selected tags.
If you are rendering the content back to an HTML page, make sure you understand XSS vulnerability & how to prevent it - i.e. always encode any user-entered text that gets rendered back onto an HTML page (> becomes > etc).

For those who are complining about Michael Tiptop's solution not working, here is the .Net4+ way of doing it:
public static string StripTags(this string markup)
{
try
{
StringReader sr = new StringReader(markup);
XPathDocument doc;
using (XmlReader xr = XmlReader.Create(sr,
new XmlReaderSettings()
{
ConformanceLevel = ConformanceLevel.Fragment
// for multiple roots
}))
{
doc = new XPathDocument(xr);
}
return doc.CreateNavigator().Value; // .Value is similar to .InnerText of
// XmlDocument or JavaScript's innerText
}
catch
{
return string.Empty;
}
}

using System.Text.RegularExpressions;
string str = Regex.Replace(HttpUtility.HtmlDecode(HTMLString), "<.*?>", string.Empty);

You can also do this with AngleSharp which is an alternative to HtmlAgilityPack (not that HAP is bad). It is easier to use than HAP to get the text out of a HTML source.
var parser = new HtmlParser();
var htmlDocument = parser.ParseDocument(source);
var text = htmlDocument.Body.Text();
You can take a look at the key features section where they make a case at being "better" than HAP. I think for the most part, it is probably overkill for the current question but still, it is an interesting alternative.

For the second parameter,i.e. keep some tags, you may need some code like this by using HTMLagilityPack:
public string StripTags(HtmlNode documentNode, IList keepTags)
{
var result = new StringBuilder();
foreach (var childNode in documentNode.ChildNodes)
{
if (childNode.Name.ToLower() == "#text")
{
result.Append(childNode.InnerText);
}
else
{
if (!keepTags.Contains(childNode.Name.ToLower()))
{
result.Append(StripTags(childNode, keepTags));
}
else
{
result.Append(childNode.OuterHtml.Replace(childNode.InnerHtml, StripTags(childNode, keepTags)));
}
}
}
return result.ToString();
}
More explanation on this page: http://nalgorithm.com/2015/11/20/strip-html-tags-of-an-html-in-c-strip_html-php-equivalent/

Simply use string.StripHTML();