Inlining CSS in C#

CaffGeek picture CaffGeek · Sep 9, 2010 · Viewed 17k times · Source

I need to inline css from a stylesheet in c#.

Like how this works.

http://www.mailchimp.com/labs/inlinecss.php

The css is simple, just classes, no fancy selectors.

I was contemplating using a regex (?<rule>(?<selector>[^{}]+){(?<style>[^{}]+)})+ to strip the rules from the css, and then attempting to do simple string replaces where the classes are called, but some of the html elements already have a style tag, so I'd have to account for that as well.

Is there a simpler approach? Or something already written in c#?

UPDATE - Sep 16, 2010

I've been able to come up with a simple CSS inliner provided your html is also valid xml. It uses a regex to get all the styles in your <style /> element. Then converts the css selectors to xpath expressions, and adds the style inline to the matching elements, before any pre-existing inline style.

Note, that the CssToXpath is not fully implemented, there are some things it just can't do... yet.

CssInliner.cs

using System.Collections.Generic;
using System.Text.RegularExpressions;
using System.Xml.Linq;
using System.Xml.XPath;

namespace CssInliner
{
    public class CssInliner
    {
        private static Regex _matchStyles = new Regex("\\s*(?<rule>(?<selector>[^{}]+){(?<style>[^{}]+)})",
                                                RegexOptions.IgnoreCase
                                                | RegexOptions.CultureInvariant
                                                | RegexOptions.IgnorePatternWhitespace
                                                | RegexOptions.Compiled
                                            );

        public List<Match> Styles { get; private set; }
        public string InlinedXhtml { get; private set; }

        private XElement XhtmlDocument { get; set; }

        public CssInliner(string xhtml)
        {
            XhtmlDocument = ParseXhtml(xhtml);
            Styles = GetStyleMatches();

            foreach (var style in Styles)
            {
                if (!style.Success)
                    return;

                var cssSelector = style.Groups["selector"].Value.Trim();
                var xpathSelector = CssToXpath.Transform(cssSelector);
                var cssStyle = style.Groups["style"].Value.Trim();

                foreach (var element in XhtmlDocument.XPathSelectElements(xpathSelector))
                {
                    var inlineStyle = element.Attribute("style");

                    var newInlineStyle = cssStyle + ";";
                    if (inlineStyle != null && !string.IsNullOrEmpty(inlineStyle.Value))
                    {
                        newInlineStyle += inlineStyle.Value;
                    }

                    element.SetAttributeValue("style", newInlineStyle.Trim().NormalizeCharacter(';').NormalizeSpace());
                }
            }

            XhtmlDocument.Descendants("style").Remove();
            InlinedXhtml = XhtmlDocument.ToString();
        }

        private List<Match> GetStyleMatches()
        {
            var styles = new List<Match>();

            var styleElements = XhtmlDocument.Descendants("style");
            foreach (var styleElement in styleElements)
            {
                var matches = _matchStyles.Matches(styleElement.Value);

                foreach (Match match in matches)
                {
                    styles.Add(match);
                }
            }

            return styles;
        }

        private static XElement ParseXhtml(string xhtml)
        {
            return XElement.Parse(xhtml);
        }
    }
}

CssToXpath.cs

using System.Text.RegularExpressions;

namespace CssInliner
{
    public static class CssToXpath
    {
        public static string Transform(string css)
        {
            #region Translation Rules
            // References:  http://ejohn.org/blog/xpath-css-selectors/
            //              http://code.google.com/p/css2xpath/source/browse/trunk/src/css2xpath.js
            var regexReplaces = new[] {
                                          // add @ for attribs
                                          new RegexReplace {
                                              Regex = new Regex(@"\[([^\]~\$\*\^\|\!]+)(=[^\]]+)?\]", RegexOptions.Multiline),
                                              Replace = @"[@$1$2]"
                                          },
                                          //  multiple queries
                                          new RegexReplace {
                                              Regex = new Regex(@"\s*,\s*", RegexOptions.Multiline),
                                              Replace = @"|"
                                          },
                                          // , + ~ >
                                          new RegexReplace {
                                              Regex = new Regex(@"\s*(\+|~|>)\s*", RegexOptions.Multiline),
                                              Replace = @"$1"
                                          },
                                          //* ~ + >
                                          new RegexReplace {
                                              Regex = new Regex(@"([a-zA-Z0-9_\-\*])~([a-zA-Z0-9_\-\*])", RegexOptions.Multiline),
                                              Replace = @"$1/following-sibling::$2"
                                          },
                                          new RegexReplace {
                                              Regex = new Regex(@"([a-zA-Z0-9_\-\*])\+([a-zA-Z0-9_\-\*])", RegexOptions.Multiline),
                                              Replace = @"$1/following-sibling::*[1]/self::$2"
                                          },
                                          new RegexReplace {
                                              Regex = new Regex(@"([a-zA-Z0-9_\-\*])>([a-zA-Z0-9_\-\*])", RegexOptions.Multiline),
                                              Replace = @"$1/$2"
                                          },
                                          // all unescaped stuff escaped
                                          new RegexReplace {
                                              Regex = new Regex(@"\[([^=]+)=([^'|""][^\]]*)\]", RegexOptions.Multiline),
                                              Replace = @"[$1='$2']"
                                          },
                                          // all descendant or self to //
                                          new RegexReplace {
                                              Regex = new Regex(@"(^|[^a-zA-Z0-9_\-\*])(#|\.)([a-zA-Z0-9_\-]+)", RegexOptions.Multiline),
                                              Replace = @"$1*$2$3"
                                          },
                                          new RegexReplace {
                                              Regex = new Regex(@"([\>\+\|\~\,\s])([a-zA-Z\*]+)", RegexOptions.Multiline),
                                              Replace = @"$1//$2"
                                          },
                                          new RegexReplace {
                                              Regex = new Regex(@"\s+\/\/", RegexOptions.Multiline),
                                              Replace = @"//"
                                          },
                                          // :first-child
                                          new RegexReplace {
                                              Regex = new Regex(@"([a-zA-Z0-9_\-\*]+):first-child", RegexOptions.Multiline),
                                              Replace = @"*[1]/self::$1"
                                          },
                                          // :last-child
                                          new RegexReplace {
                                              Regex = new Regex(@"([a-zA-Z0-9_\-\*]+):last-child", RegexOptions.Multiline),
                                              Replace = @"$1[not(following-sibling::*)]"
                                          },
                                          // :only-child
                                          new RegexReplace {
                                              Regex = new Regex(@"([a-zA-Z0-9_\-\*]+):only-child", RegexOptions.Multiline),
                                              Replace = @"*[last()=1]/self::$1"
                                          },
                                          // :empty
                                          new RegexReplace {
                                              Regex = new Regex(@"([a-zA-Z0-9_\-\*]+):empty", RegexOptions.Multiline),
                                              Replace = @"$1[not(*) and not(normalize-space())]"
                                          },
                                          // |= attrib
                                          new RegexReplace {
                                              Regex = new Regex(@"\[([a-zA-Z0-9_\-]+)\|=([^\]]+)\]", RegexOptions.Multiline),
                                              Replace = @"[@$1=$2 or starts-with(@$1,concat($2,'-'))]"
                                          },
                                          // *= attrib
                                          new RegexReplace {
                                              Regex = new Regex(@"\[([a-zA-Z0-9_\-]+)\*=([^\]]+)\]", RegexOptions.Multiline),
                                              Replace = @"[contains(@$1,$2)]"
                                          },
                                          // ~= attrib
                                          new RegexReplace {
                                              Regex = new Regex(@"\[([a-zA-Z0-9_\-]+)~=([^\]]+)\]", RegexOptions.Multiline),
                                              Replace = @"[contains(concat(' ',normalize-space(@$1),' '),concat(' ',$2,' '))]"
                                          },
                                          // ^= attrib
                                          new RegexReplace {
                                              Regex = new Regex(@"\[([a-zA-Z0-9_\-]+)\^=([^\]]+)\]", RegexOptions.Multiline),
                                              Replace = @"[starts-with(@$1,$2)]"
                                          },
                                          // != attrib
                                          new RegexReplace {
                                              Regex = new Regex(@"\[([a-zA-Z0-9_\-]+)\!=([^\]]+)\]", RegexOptions.Multiline),
                                              Replace = @"[not(@$1) or @$1!=$2]"
                                          },
                                          // ids
                                          new RegexReplace {
                                              Regex = new Regex(@"#([a-zA-Z0-9_\-]+)", RegexOptions.Multiline),
                                              Replace = @"[@id='$1']"
                                          },
                                          // classes
                                          new RegexReplace {
                                              Regex = new Regex(@"\.([a-zA-Z0-9_\-]+)", RegexOptions.Multiline),
                                              Replace = @"[contains(concat(' ',normalize-space(@class),' '),' $1 ')]"
                                          },
                                          // normalize multiple filters
                                          new RegexReplace {
                                              Regex = new Regex(@"\]\[([^\]]+)", RegexOptions.Multiline),
                                              Replace = @" and ($1)"
                                          },

                                      };
            #endregion

            foreach (var regexReplace in regexReplaces)
            {
                css = regexReplace.Regex.Replace(css, regexReplace.Replace);
            }

            return "//" + css;
        }
    }

    struct RegexReplace
    {
        public Regex Regex;
        public string Replace;
    }
}

And some tests

    [TestMethod]
    public void TestCssToXpathRules()
    {
        var translations = new Dictionary<string, string>
                               {
                                   { "*", "//*" }, 
                                   { "p", "//p" }, 
                                   { "p > *", "//p/*" }, 
                                   { "#foo", "//*[@id='foo']" }, 
                                   { "*[title]", "//*[@title]" }, 
                                   { ".bar", "//*[contains(concat(' ',normalize-space(@class),' '),' bar ')]" }, 
                                   { "div#test .note span:first-child", "//div[@id='test']//*[contains(concat(' ',normalize-space(@class),' '),' note ')]//*[1]/self::span" }
                               };

        foreach (var translation in translations)
        {
            var expected = translation.Value;
            var result = CssInliner.CssToXpath.Transform(translation.Key);

            Assert.AreEqual(expected, result);
        }
    }

    [TestMethod]
    public void HtmlWithMultiLineClassStyleReturnsInline()
    {
        #region var html = ...
        var html = XElement.Parse(@"<html>
                                        <head>
                                            <title>Hello, World Page!</title>
                                            <style>
                                                .redClass { 
                                                    background: red; 
                                                    color: purple; 
                                                }
                                            </style>
                                        </head>
                                        <body>
                                            <div class=""redClass"">Hello, World!</div>
                                        </body>
                                    </html>").ToString();
        #endregion

        #region const string expected ...
        var expected = XElement.Parse(@"<html>
                                            <head>
                                                <title>Hello, World Page!</title>
                                            </head>
                                            <body>
                                                <div class=""redClass"" style=""background: red; color: purple;"">Hello, World!</div>
                                            </body>
                                        </html>").ToString();
        #endregion

        var result = new CssInliner.CssInliner(html);

        Assert.AreEqual(expected, result.InlinedXhtml);
    }

There are more tests, but, they import html files for the input and expected output and I'm not posting all that!

But I should post the Normalize extension methods!

private static readonly Regex NormalizeSpaceRegex = new Regex(@"\s{2,}", RegexOptions.None);
public static string NormalizeSpace(this string data)
{
    return NormalizeSpaceRegex.Replace(data, @" ");
}

public static string NormalizeCharacter(this string data, char character)
{
    var normalizeCharacterRegex = new Regex(character + "{2,}", RegexOptions.None);
    return normalizeCharacterRegex.Replace(data, character.ToString());
}

Answer

MartinHN picture MartinHN · Jun 10, 2011

I have a project on Github that makes CSS inline. It's very simple, and support mobile styles. Read more on my blog: http://martinnormark.com/move-css-inline-premailer-net