1 files changed, 186 insertions, 0 deletions
diff --git a/utils/markdown/html.go b/utils/markdown/html.go
new file mode 100644
index 000000000..8d8e02c55
--- /dev/null
+++ b/utils/markdown/html.go
@@ -0,0 +1,186 @@
+// Copyright (c) 2017-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package markdown
+
+import (
+	"fmt"
+	"strings"
+)
+
+var htmlEscaper = strings.NewReplacer(
+	`&`, "&amp;",
+	`<`, "&lt;",
+	`>`, "&gt;",
+	`"`, "&quot;",
+)
+
+// RenderHTML produces HTML with the same behavior as the example renderer used in the CommonMark
+// reference materials except for one slight difference: for brevity, no unnecessary whitespace is
+// inserted between elements. The output is not defined by the CommonMark spec, and it exists
+// primarily as an aid in testing.
+func RenderHTML(markdown string) string {
+	return RenderBlockHTML(Parse(markdown))
+}
+
+func RenderBlockHTML(block Block, referenceDefinitions []*ReferenceDefinition) (result string) {
+	return renderBlockHTML(block, referenceDefinitions, false)
+}
+
+func renderBlockHTML(block Block, referenceDefinitions []*ReferenceDefinition, isTightList bool) (result string) {
+	switch v := block.(type) {
+	case *Document:
+		for _, block := range v.Children {
+			result += RenderBlockHTML(block, referenceDefinitions)
+		}
+	case *Paragraph:
+		if len(v.Text) == 0 {
+			return
+		}
+		if !isTightList {
+			result += "<p>"
+		}
+		for _, inline := range v.ParseInlines(referenceDefinitions) {
+			result += RenderInlineHTML(inline)
+		}
+		if !isTightList {
+			result += "</p>"
+		}
+	case *List:
+		if v.IsOrdered {
+			if v.OrderedStart != 1 {
+				result += fmt.Sprintf(`<ol start="%v">`, v.OrderedStart)
+			} else {
+				result += "<ol>"
+			}
+		} else {
+			result += "<ul>"
+		}
+		for _, block := range v.Children {
+			result += renderBlockHTML(block, referenceDefinitions, !v.IsLoose)
+		}
+		if v.IsOrdered {
+			result += "</ol>"
+		} else {
+			result += "</ul>"
+		}
+	case *ListItem:
+		result += "<li>"
+		for _, block := range v.Children {
+			result += renderBlockHTML(block, referenceDefinitions, isTightList)
+		}
+		result += "</li>"
+	case *BlockQuote:
+		result += "<blockquote>"
+		for _, block := range v.Children {
+			result += RenderBlockHTML(block, referenceDefinitions)
+		}
+		result += "</blockquote>"
+	case *FencedCode:
+		if info := v.Info(); info != "" {
+			language := strings.Fields(info)[0]
+			result += `<pre><code class="language-` + htmlEscaper.Replace(language) + `">`
+		} else {
+			result += "<pre><code>"
+		}
+		result += htmlEscaper.Replace(v.Code()) + "</code></pre>"
+	case *IndentedCode:
+		result += "<pre><code>" + htmlEscaper.Replace(v.Code()) + "</code></pre>"
+	default:
+		panic(fmt.Sprintf("missing case for type %T", v))
+	}
+	return
+}
+
+func escapeURL(url string) (result string) {
+	for i := 0; i < len(url); {
+		switch b := url[i]; b {
+		case ';', '/', '?', ':', '@', '&', '=', '+', '$', ',', '-', '_', '.', '!', '~', '*', '\'', '(', ')', '#':
+			result += string(b)
+			i++
+		default:
+			if b == '%' && i+2 < len(url) && isHexByte(url[i+1]) && isHexByte(url[i+2]) {
+				result += url[i : i+3]
+				i += 3
+			} else if (b >= 'a' && b <= 'z') || (b >= 'A' && b <= 'Z') || (b >= '0' && b <= '9') {
+				result += string(b)
+				i++
+			} else {
+				result += fmt.Sprintf("%%%0X", b)
+				i++
+			}
+		}
+	}
+	return
+}
+
+func RenderInlineHTML(inline Inline) (result string) {
+	switch v := inline.(type) {
+	case *Text:
+		return htmlEscaper.Replace(v.Text)
+	case *HardLineBreak:
+		return "<br />"
+	case *SoftLineBreak:
+		return "\n"
+	case *CodeSpan:
+		return "<code>" + htmlEscaper.Replace(v.Code) + "</code>"
+	case *InlineImage:
+		result += `<img src="` + htmlEscaper.Replace(escapeURL(v.Destination())) + `" alt="` + htmlEscaper.Replace(renderImageAltText(v.Children)) + `"`
+		if title := v.Title(); title != "" {
+			result += ` title="` + htmlEscaper.Replace(title) + `"`
+		}
+		result += ` />`
+	case *ReferenceImage:
+		result += `<img src="` + htmlEscaper.Replace(escapeURL(v.Destination())) + `" alt="` + htmlEscaper.Replace(renderImageAltText(v.Children)) + `"`
+		if title := v.Title(); title != "" {
+			result += ` title="` + htmlEscaper.Replace(title) + `"`
+		}
+		result += ` />`
+	case *InlineLink:
+		result += `<a href="` + htmlEscaper.Replace(escapeURL(v.Destination())) + `"`
+		if title := v.Title(); title != "" {
+			result += ` title="` + htmlEscaper.Replace(title) + `"`
+		}
+		result += `>`
+		for _, inline := range v.Children {
+			result += RenderInlineHTML(inline)
+		}
+		result += "</a>"
+	case *ReferenceLink:
+		result += `<a href="` + htmlEscaper.Replace(escapeURL(v.Destination())) + `"`
+		if title := v.Title(); title != "" {
+			result += ` title="` + htmlEscaper.Replace(title) + `"`
+		}
+		result += `>`
+		for _, inline := range v.Children {
+			result += RenderInlineHTML(inline)
+		}
+		result += "</a>"
+	default:
+		panic(fmt.Sprintf("missing case for type %T", v))
+	}
+	return
+}
+
+func renderImageAltText(children []Inline) (result string) {
+	for _, inline := range children {
+		result += renderImageChildAltText(inline)
+	}
+	return
+}
+
+func renderImageChildAltText(inline Inline) (result string) {
+	switch v := inline.(type) {
+	case *Text:
+		return v.Text
+	case *InlineImage:
+		for _, inline := range v.Children {
+			result += renderImageChildAltText(inline)
+		}
+	case *InlineLink:
+		for _, inline := range v.Children {
+			result += renderImageChildAltText(inline)
+		}
+	}
+	return
+}