c# Truncate HTML safely for article summary
- by WickedW
Hi All,
Does anyone have a c# variation of this?
This is so I can take some html and display it without breaking as a summary lead in to an article?
http://stackoverflow.com/questions/1193500/php-truncate-html-ignoring-tags
Save me from reinventing the wheel!
Thank you very much
---------- edit ------------------
Sorry, new here, and your right, should have phrased the question better, heres a bit more info
I wish to take a html string and truncate it to a set number of words (or even char length) so I can then show the start of it as a summary (which then leads to the main article). I wish to preserve the html so I can show the links etc in preview.
The main issue I have to solve is the fact that we may well end up with unclosed html tags if we truncate in the middle of 1 or more tags!
The idea I have for solution is to
a) truncate the html to N words (words better but chars ok) first (be sure not to stop in the middle of a tag and truncate a require attribute)
b) work through the opened html tags in this truncated string (maybe stick them on stack as I go?)
c) then work through the closing tags and ensure they match the ones on stack as I pop them off?
d) if any open tags left on stack after this, then write them to end of truncated string and html should be good to go!!!!
-- edit 12112009
Here is what I have bumbled together so far as a unittest file in VS2008, this 'may' help someone in future
My hack attempts based on Jan code are at top for char version + word version (DISCLAIMER: this is dirty rough code!! on my part)
I assume working with 'well-formed' HTML in all cases (but not necessarily a full document with a root node as per XML version)
Abels XML version is at bottom, but not yet got round to fully getting tests to run on this yet (plus need to understand the code) ...
I will update when I get chance to refine
having trouble with posting code? is there no upload facility on stack?
Thanks for all comments :)
using System;
using System.Collections.Generic;
using System.Text.RegularExpressions;
using System.Xml;
using System.Xml.XPath;
using Microsoft.VisualStudio.TestTools.UnitTesting;
namespace PINET40TestProject
{
[TestClass]
public class UtilityUnitTest
{
public static string TruncateHTMLSafeishChar(string text, int charCount)
{
bool inTag = false;
int cntr = 0;
int cntrContent = 0;
// loop through html, counting only viewable content
foreach (Char c in text)
{
if (cntrContent == charCount) break;
cntr++;
if (c == '<')
{
inTag = true;
continue;
}
if (c == '>')
{
inTag = false;
continue;
}
if (!inTag) cntrContent++;
}
string substr = text.Substring(0, cntr);
//search for nonclosed tags
MatchCollection openedTags = new Regex("<[^/](.|\n)*?>").Matches(substr);
MatchCollection closedTags = new Regex("<[/](.|\n)*?>").Matches(substr);
// create stack
Stack<string> opentagsStack = new Stack<string>();
Stack<string> closedtagsStack = new Stack<string>();
// to be honest, this seemed like a good idea then I got lost along the way
// so logic is probably hanging by a thread!!
foreach (Match tag in openedTags)
{
string openedtag = tag.Value.Substring(1, tag.Value.Length - 2);
// strip any attributes, sure we can use regex for this!
if (openedtag.IndexOf(" ") >= 0)
{
openedtag = openedtag.Substring(0, openedtag.IndexOf(" "));
}
// ignore brs as self-closed
if (openedtag.Trim() != "br")
{
opentagsStack.Push(openedtag);
}
}
foreach (Match tag in closedTags)
{
string closedtag = tag.Value.Substring(2, tag.Value.Length - 3);
closedtagsStack.Push(closedtag);
}
if (closedtagsStack.Count < opentagsStack.Count)
{
while (opentagsStack.Count > 0)
{
string tagstr = opentagsStack.Pop();
if (closedtagsStack.Count == 0 || tagstr != closedtagsStack.Peek())
{
substr += "</" + tagstr + ">";
}
else
{
closedtagsStack.Pop();
}
}
}
return substr;
}
public static string TruncateHTMLSafeishWord(string text, int wordCount)
{
bool inTag = false;
int cntr = 0;
int cntrWords = 0;
Char lastc = ' ';
// loop through html, counting only viewable content
foreach (Char c in text)
{
if (cntrWords == wordCount) break;
cntr++;
if (c == '<')
{
inTag = true;
continue;
}
if (c == '>')
{
inTag = false;
continue;
}
if (!inTag)
{
// do not count double spaces, and a space not in a tag counts as a word
if (c == 32 && lastc != 32)
cntrWords++;
}
}
string substr = text.Substring(0, cntr) + " ...";
//search for nonclosed tags
MatchCollection openedTags = new Regex("<[^/](.|\n)*?>").Matches(substr);
MatchCollection closedTags = new Regex("<[/](.|\n)*?>").Matches(substr);
// create stack
Stack<string> opentagsStack = new Stack<string>();
Stack<string> closedtagsStack = new Stack<string>();
foreach (Match tag in openedTags)
{
string openedtag = tag.Value.Substring(1, tag.Value.Length - 2);
// strip any attributes, sure we can use regex for this!
if (openedtag.IndexOf(" ") >= 0)
{
openedtag = openedtag.Substring(0, openedtag.IndexOf(" "));
}
// ignore brs as self-closed
if (openedtag.Trim() != "br")
{
opentagsStack.Push(openedtag);
}
}
foreach (Match tag in closedTags)
{
string closedtag = tag.Value.Substring(2, tag.Value.Length - 3);
closedtagsStack.Push(closedtag);
}
if (closedtagsStack.Count < opentagsStack.Count)
{
while (opentagsStack.Count > 0)
{
string tagstr = opentagsStack.Pop();
if (closedtagsStack.Count == 0 || tagstr != closedtagsStack.Peek())
{
substr += "</" + tagstr + ">";
}
else
{
closedtagsStack.Pop();
}
}
}
return substr;
}
public static string TruncateHTMLSafeishCharXML(string text, int charCount)
{
// your data, probably comes from somewhere, or as params to a methodint
XmlDocument xml = new XmlDocument();
xml.LoadXml(text);
// create a navigator, this is our primary tool
XPathNavigator navigator = xml.CreateNavigator();
XPathNavigator breakPoint = null;
// find the text node we need:
while (navigator.MoveToFollowing(XPathNodeType.Text))
{
string lastText = navigator.Value.Substring(0, Math.Min(charCount, navigator.Value.Length));
charCount -= navigator.Value.Length;
if (charCount <= 0)
{
// truncate the last text. Here goes your "search word boundary" code:
navigator.SetValue(lastText);
breakPoint = navigator.Clone();
break;
}
}
// first remove text nodes, because Microsoft unfortunately merges them without asking
while (navigator.MoveToFollowing(XPathNodeType.Text))
{
if (navigator.ComparePosition(breakPoint) == XmlNodeOrder.After)
{
navigator.DeleteSelf();
}
}
// moves to parent, then move the rest
navigator.MoveTo(breakPoint);
while (navigator.MoveToFollowing(XPathNodeType.Element))
{
if (navigator.ComparePosition(breakPoint) == XmlNodeOrder.After)
{
navigator.DeleteSelf();
}
}
// moves to parent
// then remove *all* empty nodes to clean up (not necessary):
// TODO, add empty elements like <br />, <img /> as exclusion
navigator.MoveToRoot();
while (navigator.MoveToFollowing(XPathNodeType.Element))
{
while (!navigator.HasChildren && (navigator.Value ?? "").Trim() == "")
{
navigator.DeleteSelf();
}
}
// moves to parent
navigator.MoveToRoot();
return navigator.InnerXml;
}
[TestMethod]
public void TestTruncateHTMLSafeish()
{
// Case where we just make it to start of HREF (so effectively an empty link)
// 'simple' nested none attributed tags
Assert.AreEqual(@"<h1>1234</h1><b><i>56789</i>012</b>",
TruncateHTMLSafeishChar(
@"<h1>1234</h1><b><i>56789</i>012345</b>",
12));
// In middle of a!
Assert.AreEqual(@"<h1>1234</h1><a href=""testurl""><b>567</b></a>",
TruncateHTMLSafeishChar(
@"<h1>1234</h1><a href=""testurl""><b>5678</b></a><i><strong>some italic nested in string</strong></i>",
7));
// more
Assert.AreEqual(@"<div><b><i><strong>1</strong></i></b></div>",
TruncateHTMLSafeishChar(
@"<div><b><i><strong>12</strong></i></b></div>",
1));
// br
Assert.AreEqual(@"<h1>1 3 5</h1><br />6",
TruncateHTMLSafeishChar(
@"<h1>1 3 5</h1><br />678<br />",
6));
}
[TestMethod]
public void TestTruncateHTMLSafeishWord()
{
// zero case
Assert.AreEqual(@" ...",
TruncateHTMLSafeishWord(
@"",
5));
// 'simple' nested none attributed tags
Assert.AreEqual(@"<h1>one two <br /></h1><b><i>three ...</i></b>",
TruncateHTMLSafeishWord(
@"<h1>one two <br /></h1><b><i>three </i>four</b>",
3), "we have added ' ...' to end of summary");
// In middle of a!
Assert.AreEqual(@"<h1>one two three </h1><a href=""testurl""><b class=""mrclass"">four ...</b></a>",
TruncateHTMLSafeishWord(
@"<h1>one two three </h1><a href=""testurl""><b class=""mrclass"">four five </b></a><i><strong>some italic nested in string</strong></i>",
4));
// start of h1
Assert.AreEqual(@"<h1>one two three ...</h1>",
TruncateHTMLSafeishWord(
@"<h1>one two three </h1><a href=""testurl""><b>four five </b></a><i><strong>some italic nested in string</strong></i>",
3));
// more than words available
Assert.AreEqual(@"<h1>one two three </h1><a href=""testurl""><b>four five </b></a><i><strong>some italic nested in string</strong></i> ...",
TruncateHTMLSafeishWord(
@"<h1>one two three </h1><a href=""testurl""><b>four five </b></a><i><strong>some italic nested in string</strong></i>",
99));
}
[TestMethod]
public void TestTruncateHTMLSafeishWordXML()
{
// zero case
Assert.AreEqual(@" ...",
TruncateHTMLSafeishWord(
@"",
5));
// 'simple' nested none attributed tags
string output = TruncateHTMLSafeishCharXML(
@"<body><h1>one two </h1><b><i>three </i>four</b></body>",
13);
Assert.AreEqual(@"<body>\r\n <h1>one two </h1>\r\n <b>\r\n <i>three</i>\r\n </b>\r\n</body>", output,
"XML version, no ... yet and addeds '\r\n + spaces?' to format document");
// In middle of a!
Assert.AreEqual(@"<h1>one two three </h1><a href=""testurl""><b class=""mrclass"">four ...</b></a>",
TruncateHTMLSafeishCharXML(
@"<body><h1>one two three </h1><a href=""testurl""><b class=""mrclass"">four five </b></a><i><strong>some italic nested in string</strong></i></body>",
4));
// start of h1
Assert.AreEqual(@"<h1>one two three ...</h1>",
TruncateHTMLSafeishCharXML(
@"<h1>one two three </h1><a href=""testurl""><b>four five </b></a><i><strong>some italic nested in string</strong></i>",
3));
// more than words available
Assert.AreEqual(@"<h1>one two three </h1><a href=""testurl""><b>four five </b></a><i><strong>some italic nested in string</strong></i> ...",
TruncateHTMLSafeishCharXML(
@"<h1>one two three </h1><a href=""testurl""><b>four five </b></a><i><strong>some italic nested in string</strong></i>",
99));
}
}
}
