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Merged
FlorianRappl merged 1 commit into from
Mar 30, 2026
Merged

Optimize CSS parser performance #212

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2 changes: 1 addition & 1 deletion src/AngleSharp.Css/Converters/DictionaryValueConverter.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -25,7 +25,7 @@ public ICssValue Convert(StringSource source)

if (ident != null && _values.TryGetValue(ident, out mode))
{
return new CssConstantValue<T>(ident.ToLowerInvariant(), mode);
return new CssConstantValue<T>(ident.ToLowerFast(), mode);
}

source.BackTo(pos);
Expand Down
5 changes: 5 additions & 0 deletions src/AngleSharp.Css/Converters/PeriodicValueConverter.cs
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Expand Up @@ -34,6 +34,11 @@ public ICssValue Convert(StringSource source)

if (length > 0)
{
if (length == 4)
{
return new CssPeriodicValue(options);
}

var values = new ICssValue[length];
Array.Copy(options, values, length);
return new CssPeriodicValue(values);
Expand Down
2 changes: 1 addition & 1 deletion src/AngleSharp.Css/Dom/Internal/CssProperty.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -29,7 +29,7 @@ internal class CssProperty : ICssProperty

internal CssProperty(String name, IValueConverter converter, PropertyFlags flags = PropertyFlags.None, ICssValue value = null, Boolean important = false)
{
_name = name.StartsWith("--") ? name : name.ToLowerInvariant();
_name = name.StartsWith("--") ? name : name.ToLowerFast();
_converter = converter;
_flags = flags;
_value = value;
Expand Down
92 changes: 68 additions & 24 deletions src/AngleSharp.Css/Dom/Internal/CssStyleDeclaration.cs
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Expand Up @@ -19,6 +19,7 @@ sealed class CssStyleDeclaration : ICssStyleDeclaration
#region Fields

private readonly List<ICssProperty> _declarations;
private readonly Dictionary<String, Int32> _declarationIndex;
private readonly IBrowsingContext _context;
private ICssRule _parent;
private Boolean _updating;
Expand All @@ -36,6 +37,7 @@ sealed class CssStyleDeclaration : ICssStyleDeclaration
public CssStyleDeclaration(IBrowsingContext context)
{
_declarations = new List<ICssProperty>();
_declarationIndex = new Dictionary<String, Int32>(StringComparer.OrdinalIgnoreCase);
_context = context;
}

Expand Down Expand Up @@ -77,9 +79,9 @@ public String CssText

public ICssProperty GetProperty(String name)
{
for (var i = 0; i < _declarations.Count; i++)
if (_declarationIndex.TryGetValue(name, out var index) && index < _declarations.Count)
{
var declaration = _declarations[i];
var declaration = _declarations[index];

if (declaration.Name.Isi(name))
{
Expand All @@ -100,6 +102,7 @@ public void Update(String value)
if (!_updating)
{
_declarations.Clear();
_declarationIndex.Clear();

if (!String.IsNullOrEmpty(value))
{
Expand All @@ -109,6 +112,7 @@ public void Update(String value)
if (decl != null)
{
_declarations.AddRange(decl);
RebuildIndex();
}
}
}
Expand Down Expand Up @@ -304,12 +308,14 @@ public void SetProperty(String propertyName, String propertyValue, String priori

public void AddProperty(ICssProperty declaration)
{
_declarationIndex[declaration.Name] = _declarations.Count;
_declarations.Add(declaration);
}

public void RemoveProperty(ICssProperty declaration)
{
_declarations.Remove(declaration);
RebuildIndex();
}

#endregion
Expand Down Expand Up @@ -359,14 +365,24 @@ private void RemovePropertyByName(String propertyName)
var info = _context.GetDeclarationInfo(propertyName);
var longhands = info.Longhands;

for (var i = 0; i < _declarations.Count; i++)
if (_declarationIndex.TryGetValue(propertyName, out var index) && index < _declarations.Count &&
_declarations[index].Name.Is(propertyName))
{
var declaration = _declarations[i];

if (declaration.Name.Is(propertyName))
_declarations.RemoveAt(index);
RebuildIndex();
}
else
{
for (var i = 0; i < _declarations.Count; i++)
{
_declarations.RemoveAt(i);
break;
var declaration = _declarations[i];

if (declaration.Name.Is(propertyName))
{
_declarations.RemoveAt(i);
RebuildIndex();
break;
}
}
}

Expand All @@ -389,23 +405,39 @@ private void ChangeDeclarations(IEnumerable<ICssProperty> decls, Predicate<ICssP
{
var skip = defaultSkip(newdecl);

for (var i = 0; i < _declarations.Count; i++)
if (_declarationIndex.TryGetValue(newdecl.Name, out var idx) && idx < _declarations.Count &&
_declarations[idx].Name.Is(newdecl.Name))
{
var olddecl = _declarations[i];

if (olddecl.Name.Is(newdecl.Name))
if (removeExisting.Invoke(_declarations[idx], newdecl))
{
if (removeExisting.Invoke(olddecl, newdecl))
{
_declarations.RemoveAt(i);
skip = false;
}
else
_declarations.RemoveAt(idx);
skip = false;
}
else
{
skip = true;
}
}
else
{
for (var i = 0; i < _declarations.Count; i++)
{
var olddecl = _declarations[i];

if (olddecl.Name.Is(newdecl.Name))
{
skip = true;
}
if (removeExisting.Invoke(olddecl, newdecl))
{
_declarations.RemoveAt(i);
skip = false;
}
else
{
skip = true;
}

break;
break;
}
}
}

Expand All @@ -416,13 +448,14 @@ private void ChangeDeclarations(IEnumerable<ICssProperty> decls, Predicate<ICssP
}

_declarations.AddRange(declarations);
RebuildIndex();
}

private void SetLonghand(ICssProperty property)
{
for (var i = 0; i < _declarations.Count; i++)
if (_declarationIndex.TryGetValue(property.Name, out var index) && index < _declarations.Count)
{
var declaration = _declarations[i];
var declaration = _declarations[index];

if (declaration.Name.Is(property.Name))
{
Expand All @@ -431,11 +464,12 @@ private void SetLonghand(ICssProperty property)
return;
}

_declarations[i] = property;
_declarations[index] = property;
return;
}
}

_declarationIndex[property.Name] = _declarations.Count;
_declarations.Add(property);
}

Expand All @@ -452,6 +486,16 @@ private void SetShorthand(ICssProperty shorthand)
}
}

private void RebuildIndex()
{
_declarationIndex.Clear();

for (var i = 0; i < _declarations.Count; i++)
{
_declarationIndex[_declarations[i].Name] = i;
}
}

private void RaiseChanged()
{
if (!_updating)
Expand Down
19 changes: 19 additions & 0 deletions src/AngleSharp.Css/Extensions/StringExtensions.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -87,5 +87,24 @@ public static String CssUrl(this String value)
var argument = value.CssString();
return Keywords.Url.CssFunction(argument);
}

/// <summary>
/// Converts to lowercase, returning the original string if it is already lowercase.
/// Avoids allocation for the common case of already-lowercase CSS identifiers.
/// </summary>
internal static String ToLowerFast(this String value)
{
for (var i = 0; i < value.Length; i++)
{
var c = value[i];

if (c >= 'A' && c <= 'Z')
{
return value.ToLowerInvariant();
}
}

return value;
}
}
}
109 changes: 47 additions & 62 deletions src/AngleSharp.Css/Parser/CssBuilder.cs
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Original file line number Diff line number Diff line change
@@ -1,11 +1,13 @@
#nullable disable
namespace AngleSharp.Css.Parser
{
using AngleSharp.Common;
using AngleSharp.Css.Dom;
using AngleSharp.Css.Parser.Tokens;
using AngleSharp.Dom;
using AngleSharp.Text;
using System;
using System.Collections.Generic;

/// <summary>
/// See http://dev.w3.org/csswg/css-syntax/#parsing for details.
Expand All @@ -14,6 +16,22 @@ sealed class CssBuilder
{
#region Fields

private static readonly Dictionary<String, Int32> AtRuleMap = new Dictionary<String, Int32>(StringComparer.OrdinalIgnoreCase)
{
{ RuleNames.Media, 1 },
{ RuleNames.FontFace, 2 },
{ RuleNames.Keyframes, 3 },
{ RuleNames.Import, 4 },
{ RuleNames.Charset, 5 },
{ RuleNames.Namespace, 6 },
{ RuleNames.Page, 7 },
{ RuleNames.Supports, 8 },
{ RuleNames.ViewPort, 9 },
{ RuleNames.Document, 10 },
{ RuleNames.CounterStyle, 11 },
{ RuleNames.FontFeatureValues, 12 },
};

private readonly CssTokenizer _tokenizer;
private readonly CssParserOptions _options;
private readonly IBrowsingContext _context;
Expand Down Expand Up @@ -67,67 +85,26 @@ private ICssRule CreateStyleRule(ICssStyleSheet sheet, CssToken token)

private ICssRule CreateAtRule(ICssStyleSheet sheet, CssToken token)
{
if (token.Data.Is(RuleNames.Media))
{
var rule = new CssMediaRule(sheet);
return CreateMedia(rule, token);
}
else if (token.Data.Is(RuleNames.FontFace))
{
var rule = new CssFontFaceRule(sheet);
return CreateFontFace(rule, token);
}
else if (token.Data.Is(RuleNames.Keyframes))
{
var rule = new CssKeyframesRule(sheet);
return CreateKeyframes(rule, token);
}
else if (token.Data.Is(RuleNames.Import))
{
var rule = new CssImportRule(sheet);
return CreateImport(rule, token);
}
else if (token.Data.Is(RuleNames.Charset))
{
var rule = new CssCharsetRule(sheet);
return CreateCharset(rule, token);
}
else if (token.Data.Is(RuleNames.Namespace))
{
var rule = new CssNamespaceRule(sheet);
return CreateNamespace(rule, token);
}
else if (token.Data.Is(RuleNames.Page))
{
var rule = new CssPageRule(sheet);
return CreatePage(rule, token);
}
else if (token.Data.Is(RuleNames.Supports))
if (AtRuleMap.TryGetValue(token.Data, out var ruleId))
{
var rule = new CssSupportsRule(sheet);
return CreateSupports(rule, token);
}
else if (token.Data.Is(RuleNames.ViewPort))
{
var rule = new CssViewportRule(sheet);
return CreateViewport(rule, token);
}
else if (token.Data.Is(RuleNames.Document))
{
var rule = new CssDocumentRule(sheet);
return CreateDocument(rule, token);
}
else if (token.Data.Is(RuleNames.CounterStyle))
{
var rule = new CssCounterStyleRule(sheet);
return CreateCounterStyle(rule, token);
}
else if (token.Data.Is(RuleNames.FontFeatureValues))
{
var rule = new CssFontFeatureValuesRule(sheet);
return CreateFontFeatureValues(rule, token);
switch (ruleId)
{
case 1: return CreateMedia(new CssMediaRule(sheet), token);
case 2: return CreateFontFace(new CssFontFaceRule(sheet), token);
case 3: return CreateKeyframes(new CssKeyframesRule(sheet), token);
case 4: return CreateImport(new CssImportRule(sheet), token);
case 5: return CreateCharset(new CssCharsetRule(sheet), token);
case 6: return CreateNamespace(new CssNamespaceRule(sheet), token);
case 7: return CreatePage(new CssPageRule(sheet), token);
case 8: return CreateSupports(new CssSupportsRule(sheet), token);
case 9: return CreateViewport(new CssViewportRule(sheet), token);
case 10: return CreateDocument(new CssDocumentRule(sheet), token);
case 11: return CreateCounterStyle(new CssCounterStyleRule(sheet), token);
case 12: return CreateFontFeatureValues(new CssFontFeatureValuesRule(sheet), token);
}
}
else if (_options.IsIncludingUnknownRules)

if (_options.IsIncludingUnknownRules)
{
return CreateUnknownAtRule(sheet, token);
}
Expand Down Expand Up @@ -556,10 +533,18 @@ public void CreateDeclarationWith(ICssProperties properties, ref CssToken token)
{
var name = token.Data;

while (token.Type == CssTokenType.Delim)
if (token.Type == CssTokenType.Delim)
{
token = NextToken();
name += token.Data;
var sb = StringBuilderPool.Obtain();
sb.Append(name);

while (token.Type == CssTokenType.Delim)
{
token = NextToken();
sb.Append(token.Data);
}

name = sb.ToPool();
}

token = NextToken();
Expand Down
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