private RenderedMarkdownResult GetHtmlFromMarkdownCommonMark(string markdownString, int incrementHeadersBy)
{
var output = new RenderedMarkdownResult()
{
ImagesRewritten = false,
Content = "",
ImageSourceDisallowed = false
};
var readmeWithoutBom = markdownString.StartsWith("\ufeff") ? markdownString.Replace("\ufeff", "") : markdownString;
// HTML encode markdown, except for block quotes, to block inline html.
var encodedMarkdown = EncodedBlockQuotePattern.Replace(HttpUtility.HtmlEncode(readmeWithoutBom), "> ");
var settings = CommonMarkSettings.Default.Clone();
settings.RenderSoftLineBreaksAsLineBreaks = true;
// Parse executes CommonMarkConverter's ProcessStage1 and ProcessStage2.
var document = CommonMarkConverter.Parse(encodedMarkdown, settings);
foreach (var node in document.AsEnumerable())
{
if (node.IsOpening)
{
var block = node.Block;
if (block != null)
{
switch (block.Tag)
{
// Demote heading tags so they don't overpower expander headings.
case BlockTag.AtxHeading:
case BlockTag.SetextHeading:
var level = (byte)Math.Min(block.Heading.Level + incrementHeadersBy, 6);
block.Heading = new HeadingData(level);
break;
// Decode preformatted blocks to prevent double encoding.
// Skip BlockTag.BlockQuote, which are partially decoded upfront.
case BlockTag.FencedCode:
case BlockTag.IndentedCode:
if (block.StringContent != null)
{
var content = block.StringContent.TakeFromStart(block.StringContent.Length);
var unencodedContent = HttpUtility.HtmlDecode(content);
block.StringContent.Replace(unencodedContent, 0, unencodedContent.Length);
}
break;
}
}
var inline = node.Inline;
if (inline != null)
{
if (inline.Tag == InlineTag.Link)
{
// Allow only http or https links in markdown. Transform link to https for known domains.
if (!PackageHelper.TryPrepareUrlForRendering(inline.TargetUrl, out string readyUriString))
{
inline.TargetUrl = string.Empty;
}
else
{
inline.TargetUrl = readyUriString;
}
}
else if (inline.Tag == InlineTag.Image)
{
if (_features.IsImageAllowlistEnabled())
{
if (!_imageDomainValidator.TryPrepareImageUrlForRendering(inline.TargetUrl, out string readyUriString))
{
inline.TargetUrl = string.Empty;
output.ImageSourceDisallowed = true;
}
else
{
output.ImagesRewritten = output.ImagesRewritten || (inline.TargetUrl != readyUriString);
inline.TargetUrl = readyUriString;
}
}
else
{
if (!PackageHelper.TryPrepareUrlForRendering(inline.TargetUrl, out string readyUriString, rewriteAllHttp: true))
{
inline.TargetUrl = string.Empty;
}
else
{
output.ImagesRewritten = output.ImagesRewritten || (inline.TargetUrl != readyUriString);
inline.TargetUrl = readyUriString;
}
}
}
}
}