add nip23 markdown helper.

nip23/markdown.go

@@ -0,0 +1,64 @@
+package nip23
+
+import (
+	stdhtml "html"
+	"io"
+	"regexp"
+	"strings"
+
+	"github.com/gomarkdown/markdown"
+	"github.com/gomarkdown/markdown/ast"
+	"github.com/gomarkdown/markdown/html"
+	"github.com/gomarkdown/markdown/parser"
+	"github.com/microcosm-cc/bluemonday"
+)
+
+var nostrEveryMatcher = regexp.MustCompile(`nostr:((npub|note|nevent|nprofile|naddr)1[a-z0-9]+)\b`)
+
+var renderer = html.NewRenderer(html.RendererOptions{
+	Flags: html.HrefTargetBlank | html.SkipHTML,
+	RenderNodeHook: func(w io.Writer, node ast.Node, entering bool) (ast.WalkStatus, bool) {
+		switch v := node.(type) {
+		case *ast.HTMLSpan:
+			w.Write([]byte(stdhtml.EscapeString(string(v.Literal))))
+			return ast.GoToNext, true
+		case *ast.HTMLBlock:
+			w.Write([]byte(stdhtml.EscapeString(string(v.Literal))))
+			return ast.GoToNext, true
+		}
+
+		return ast.GoToNext, false
+	},
+})
+
+func MarkdownToHTML(md string) string {
+	md = strings.ReplaceAll(md, "\u00A0", " ")
+
+	// create markdown parser with extensions
+	// this parser is stateful so it must be reinitialized every time
+	doc := parser.NewWithExtensions(
+		parser.AutoHeadingIDs |
+			parser.NoIntraEmphasis |
+			parser.FencedCode |
+			parser.Autolink |
+			parser.Footnotes |
+			parser.SpaceHeadings,
+	).Parse([]byte(md))
+
+	// create HTML renderer with extensions
+	output := string(markdown.Render(doc, renderer))
+
+	// sanitize content
+	output = sanitizeXSS(output)
+
+	return output
+}
+
+func sanitizeXSS(html string) string {
+	p := bluemonday.UGCPolicy()
+	p.RequireNoFollowOnLinks(false)
+	p.AllowElements("video", "source")
+	p.AllowAttrs("controls", "width").OnElements("video")
+	p.AllowAttrs("src", "width").OnElements("source")
+	return p.Sanitize(html)
+}