/// <summary>
/// Returns true if it is considered valid for the given parent tag to contain the
/// given child tag. Provide the parent flags, if available, to improve performance.
/// </summary>
public static bool TagMayContain(string parentTag, string childTag, HtmlTagFlag parentFlags)
{
if (parentFlags.HasFlag(HtmlTagFlag.NoChildren))
{
return(false);
}
if (parentFlags.HasFlag(HtmlTagFlag.NoNested) && parentTag.Equals(childTag, StringComparison.OrdinalIgnoreCase))
{
return(false);
}
// Attempt to catch some obviously invalid HTML structure
if (GetTagPriority(childTag) > GetTagPriority(parentTag))
{
return(false);
}
return(true);
}
/// <summary>
/// Parses the given HTML string into a number of root nodes.
/// </summary>
/// <param name="html">The HTML text to parse.</param>
public IEnumerable <HtmlNode> ParseChildren(string html)
{
TextParser parser = new TextParser(html);
HtmlElementNode rootNode = new HtmlElementNode("[Root]");
HtmlElementNode parentNode = rootNode;
string tag;
bool selfClosing;
// Loop until end of input
while (!parser.EndOfText)
{
if (parser.Peek() == HtmlRules.TagStart)
{
// Test for CDATA segments, which we store but do not parse. This includes comments.
CDataDefinition definition = HtmlRules.CDataDefinitions.FirstOrDefault(dd => parser.MatchesCurrentPosition(dd.StartText, dd.IgnoreCase));
if (definition != null)
{
parentNode.Children.Add(ParseCDataNode(parser, definition));
continue;
}
// Closing tag
if (parser.Peek(1) == HtmlRules.ForwardSlash)
{
parser.MoveAhead(2);
tag = parser.ParseWhile(c => HtmlRules.IsTagCharacter(c));
if (tag.Length > 0)
{
if (parentNode.TagName.Equals(tag, HtmlRules.TagStringComparison))
{
// Should never have matched parent if the top-level node
Debug.Assert(!parentNode.IsTopLevelNode);
parentNode = parentNode.ParentNode;
}
else
{
// Handle mismatched closing tag
int tagPriority = HtmlRules.GetTagPriority(tag);
while (!parentNode.IsTopLevelNode && tagPriority > HtmlRules.GetTagPriority(parentNode.TagName))
{
parentNode = parentNode.ParentNode;
}
if (parentNode.TagName.Equals(tag, HtmlRules.TagStringComparison))
{
Debug.Assert(!parentNode.IsTopLevelNode);
parentNode = parentNode.ParentNode;
}
}
}
parser.MoveTo(HtmlRules.TagEnd);
parser.MoveAhead();
continue;
}
// Open tag
if (ParseTag(parser, out tag))
{
HtmlTagFlag flags = HtmlRules.GetTagFlags(tag);
if (flags.HasFlag(HtmlTagFlag.HtmlHeader))
{
parentNode.Children.Add(ParseHtmlHeader(parser));
}
else if (flags.HasFlag(HtmlTagFlag.XmlHeader))
{
parentNode.Children.Add(ParseXmlHeader(parser));
}
else
{
// Parse attributes
HtmlAttributeCollection attributes = ParseAttributes(parser);
// Parse rest of tag
if (parser.Peek() == HtmlRules.ForwardSlash)
{
parser.MoveAhead();
parser.MovePastWhitespace();
selfClosing = true;
}
else
{
selfClosing = false;
}
parser.MoveTo(HtmlRules.TagEnd);
parser.MoveAhead();
// Add node
HtmlElementNode node = new HtmlElementNode(tag, attributes);
while (!HtmlRules.TagMayContain(parentNode.TagName, tag) && !parentNode.IsTopLevelNode)
{
Debug.Assert(parentNode.ParentNode != null);
parentNode = parentNode.ParentNode;
}
parentNode.Children.Add(node);
if (flags.HasFlag(HtmlTagFlag.CData))
{
// CDATA tags are treated as elements but we store and do not parse the inner content
if (!selfClosing)
{
if (ParseToClosingTag(parser, tag, out string content) && content.Length > 0)
{
node.Children.Add(new HtmlCDataNode(string.Empty, string.Empty, content));
}
}
}
else
{
if (selfClosing && flags.HasFlag(HtmlTagFlag.NoSelfClosing))
{
selfClosing = false;
}
if (!selfClosing && !flags.HasFlag(HtmlTagFlag.NoChildren))
{
parentNode = node; // Node becomes new parent
}
}
}
continue;
}
}
// Text node
int start = parser.Index;
// Text must be at least 1 character (handle '<' that is not part of a tag)
parser.MoveAhead();
parser.MoveTo(HtmlRules.TagStart);
Debug.Assert(parser.Index > start);
parentNode.Children.Add(new HtmlTextNode(parser.Extract(start, parser.Index)));
}
//
return(rootNode.Children);
}
/// <summary>
/// Parses the given HTML string into a collection of root nodes and their
/// children.
/// </summary>
/// <param name="html">The HTML text to parse.</param>
public IEnumerable <HtmlNode> ParseChildren(string?html, bool ignoreHtmlRules = false)
{
HtmlElementNode rootNode = new("[TempContainer]");
HtmlElementNode parentNode = rootNode;
Parser.Reset(html);
bool selfClosing;
string?tag;
// Loop until end of input
while (!Parser.EndOfText)
{
if (Parser.Peek() == HtmlRules.TagStart)
{
// CDATA segments (blocks we store but don't parse--includes comments)
CDataDefinition?definition = HtmlRules.CDataDefinitions.FirstOrDefault(dd => Parser.MatchesCurrentPosition(dd.StartText, dd.StartComparison));
if (definition != null)
{
parentNode.Children.Add(ParseCDataNode(definition));
continue;
}
// Closing tag
if (Parser.Peek(1) == HtmlRules.ForwardSlash)
{
Parser.Index += 2;
tag = Parser.ParseWhile(HtmlRules.IsTagCharacter);
if (tag.Length > 0)
{
if (parentNode.TagName.Equals(tag, HtmlRules.TagStringComparison))
{
// Should never have matched parent if the top-level node
if (!parentNode.IsTopLevelNode)
{
parentNode = parentNode.ParentNode;
}
}
else
{
// Handle mismatched closing tag
int tagPriority = HtmlRules.GetTagNestLevel(tag);
while (!parentNode.IsTopLevelNode && tagPriority > HtmlRules.GetTagNestLevel(parentNode.TagName))
{
parentNode = parentNode.ParentNode;
}
if (parentNode.TagName.Equals(tag, HtmlRules.TagStringComparison))
{
if (!parentNode.IsTopLevelNode)
{
parentNode = parentNode.ParentNode;
}
}
}
}
Parser.SkipTo(HtmlRules.TagEnd);
Parser.Next();
continue;
}
// Open tag
if (ParseTag(out tag))
{
HtmlTagFlag flags = ignoreHtmlRules ? HtmlTagFlag.None : HtmlRules.GetTagFlags(tag);
if (flags.HasFlag(HtmlTagFlag.HtmlHeader))
{
parentNode.Children.Add(ParseHtmlHeader());
}
else if (flags.HasFlag(HtmlTagFlag.XmlHeader))
{
parentNode.Children.Add(ParseXmlHeader());
}
else
{
// Parse attributes
HtmlAttributeCollection attributes = ParseAttributes();
// Parse rest of tag
if (Parser.Peek() == HtmlRules.ForwardSlash)
{
Parser.Next();
Parser.SkipWhiteSpace();
selfClosing = true;
}
else
{
selfClosing = false;
}
Parser.SkipTo(HtmlRules.TagEnd);
Parser.Next();
// Add node
HtmlElementNode node = new(tag, attributes);
while (!HtmlRules.TagMayContain(parentNode.TagName, tag) && !parentNode.IsTopLevelNode)
{
parentNode = parentNode.ParentNode;
}
parentNode.Children.Add(node);
if (flags.HasFlag(HtmlTagFlag.CData))
{
// CDATA tags are treated as elements but we store and do not parse the inner content
if (!selfClosing)
{
if (ParseToClosingTag(tag, out string?content) && content.Length > 0)
{
node.Children.Add(new HtmlCDataNode(string.Empty, string.Empty, content));
}
}
}
else
{
if (selfClosing && flags.HasFlag(HtmlTagFlag.NoSelfClosing))
{
selfClosing = false;
}
if (!selfClosing && !flags.HasFlag(HtmlTagFlag.NoChildren))
{
parentNode = node; // Node becomes new parent
}
}
}
continue;
}
}
// Text node: must be at least 1 character (handles '<' that was not a tag)
string text = Parser.ParseCharacter();
text += Parser.ParseTo(HtmlRules.TagStart);
parentNode.Children.Add(new HtmlTextNode(text));
}
// Return top-level nodes from nodes just parsed
return(rootNode.Children);
}
