Add support for markdown to HTML conversion (matrix). Closes #663 (#670)

This uses our own gomatrix lib with the SendHTML function which
adds HTML to formatted_body in matrix.
golang-commonmark is used to convert markdown into valid HTML.

vendor/gitlab.com/golang-commonmark/markdown/linkify.go

@@ -0,0 +1,131 @@
+// Copyright 2015 The Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package markdown
+
+import (
+	"strings"
+
+	"gitlab.com/golang-commonmark/linkify"
+)
+
+func isLinkOpen(s string) bool { return isLetter(s[1]) }
+
+func isLinkClose(s string) bool { return s[1] == '/' }
+
+func ruleLinkify(s *StateCore) {
+	blockTokens := s.Tokens
+
+	if !s.Md.Linkify {
+		return
+	}
+
+	for _, tok := range blockTokens {
+		if tok, ok := tok.(*Inline); ok {
+			tokens := tok.Children
+
+			htmlLinkLevel := 0
+
+			for i := len(tokens) - 1; i >= 0; i-- {
+				currentTok := tokens[i]
+
+				if _, ok := currentTok.(*LinkClose); ok {
+					i--
+					for tokens[i].Level() != currentTok.Level() {
+						if _, ok := tokens[i].(*LinkOpen); ok {
+							break
+						}
+						i--
+					}
+					continue
+				}
+
+				if currentTok, ok := currentTok.(*HTMLInline); ok {
+					if isLinkOpen(currentTok.Content) && htmlLinkLevel > 0 {
+						htmlLinkLevel--
+					}
+					if isLinkClose(currentTok.Content) {
+						htmlLinkLevel++
+					}
+				}
+				if htmlLinkLevel > 0 {
+					continue
+				}
+
+				if currentTok, ok := currentTok.(*Text); ok {
+					text := currentTok.Content
+					links := linkify.Links(text)
+					if len(links) == 0 {
+						continue
+					}
+
+					var nodes []Token
+					level := currentTok.Lvl
+					lastPos := 0
+
+					for _, ln := range links {
+						urlText := text[ln.Start:ln.End]
+						url := urlText
+						if ln.Scheme == "" {
+							url = "http://" + url
+						} else if ln.Scheme == "mailto:" && !strings.HasPrefix(url, "mailto:") {
+							url = "mailto:" + url
+						}
+						url = normalizeLink(url)
+						if !validateLink(url) {
+							continue
+						}
+
+						if ln.Scheme == "" {
+							urlText = strings.TrimPrefix(normalizeLinkText("http://"+urlText), "http://")
+						} else if ln.Scheme == "mailto:" && !strings.HasPrefix(urlText, "mailto:") {
+							urlText = strings.TrimPrefix(normalizeLinkText("mailto:"+urlText), "mailto:")
+						} else {
+							urlText = normalizeLinkText(urlText)
+						}
+
+						pos := ln.Start
+
+						if pos > lastPos {
+							tok := Text{
+								Content: text[lastPos:pos],
+								Lvl:     level,
+							}
+							nodes = append(nodes, &tok)
+						}
+
+						nodes = append(nodes, &LinkOpen{
+							Href: url,
+							Lvl:  level,
+						})
+						nodes = append(nodes, &Text{
+							Content: urlText,
+							Lvl:     level + 1,
+						})
+						nodes = append(nodes, &LinkClose{
+							Lvl: level,
+						})
+
+						lastPos = ln.End
+					}
+
+					if lastPos < len(text) {
+						tok := Text{
+							Content: text[lastPos:],
+							Lvl:     level,
+						}
+						nodes = append(nodes, &tok)
+					}
+
+					children := make([]Token, len(tokens)+len(nodes)-1)
+					copy(children, tokens[:i])
+					copy(children[i:], nodes)
+					copy(children[i+len(nodes):], tokens[i+1:])
+					tok.Children = children
+					tokens = children
+				}
+			}
+		}
+	}
+}