[chore/bugfix] Switch markdown from blackfriday to goldmark (#1267)

Co-authored-by: Autumn! <autumnull@posteo.net>

1 files changed, 215 insertions, 0 deletions

diff --git a/internal/text/markdownextension.go b/internal/text/markdownextension.go
new file mode 100644
index 000000000..1be1e99d6
--- /dev/null
+++ b/internal/text/markdownextension.go
@@ -0,0 +1,215 @@
+/*
+   GoToSocial
+   Copyright (C) 2021-2022 GoToSocial Authors admin@gotosocial.org
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Affero General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU Affero General Public License for more details.
+   You should have received a copy of the GNU Affero General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+package text
+
+import (
+	"context"
+	"unicode"
+
+	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
+	"github.com/superseriousbusiness/gotosocial/internal/log"
+	"github.com/superseriousbusiness/gotosocial/internal/regexes"
+	"github.com/superseriousbusiness/gotosocial/internal/util"
+	"github.com/yuin/goldmark"
+	"github.com/yuin/goldmark/ast"
+	"github.com/yuin/goldmark/parser"
+	"github.com/yuin/goldmark/renderer"
+	"github.com/yuin/goldmark/text"
+	mdutil "github.com/yuin/goldmark/util"
+)
+
+// A goldmark extension that parses potential mentions and hashtags separately from regular
+// text, so that they stay as one contiguous text fragment in the AST, and then renders
+// them separately too, to avoid scanning normal text for mentions and tags.
+
+// mention and hashtag fulfil the goldmark ast.Node interface.
+type mention struct {
+	ast.BaseInline
+	Segment text.Segment
+}
+
+type hashtag struct {
+	ast.BaseInline
+	Segment text.Segment
+}
+
+var kindMention = ast.NewNodeKind("Mention")
+var kindHashtag = ast.NewNodeKind("Hashtag")
+
+func (n *mention) Kind() ast.NodeKind {
+	return kindMention
+}
+
+func (n *hashtag) Kind() ast.NodeKind {
+	return kindHashtag
+}
+
+// Dump is used by goldmark for debugging. It is implemented only minimally because
+// it is not used in our code.
+func (n *mention) Dump(source []byte, level int) {
+	ast.DumpHelper(n, source, level, nil, nil)
+}
+
+func (n *hashtag) Dump(source []byte, level int) {
+	ast.DumpHelper(n, source, level, nil, nil)
+}
+
+// newMention and newHashtag create a goldmark ast.Node from a goldmark text.Segment.
+// The contained segment is used in rendering.
+func newMention(s text.Segment) *mention {
+	return &mention{
+		BaseInline: ast.BaseInline{},
+		Segment:    s,
+	}
+}
+
+func newHashtag(s text.Segment) *hashtag {
+	return &hashtag{
+		BaseInline: ast.BaseInline{},
+		Segment:    s,
+	}
+}
+
+// mentionParser and hashtagParser fulfil the goldmark parser.InlineParser interface.
+type mentionParser struct {
+}
+
+type hashtagParser struct {
+}
+
+func (p *mentionParser) Trigger() []byte {
+	return []byte{'@'}
+}
+
+func (p *hashtagParser) Trigger() []byte {
+	return []byte{'#'}
+}
+
+func (p *mentionParser) Parse(parent ast.Node, block text.Reader, pc parser.Context) ast.Node {
+	before := block.PrecendingCharacter()
+	line, segment := block.PeekLine()
+
+	if !unicode.IsSpace(before) {
+		return nil
+	}
+
+	// unideal for performance but makes use of existing regex
+	loc := regexes.MentionFinder.FindIndex(line)
+	switch {
+	case loc == nil:
+		fallthrough
+	case loc[0] != 0: // fail if not found at start
+		return nil
+	default:
+		block.Advance(loc[1])
+		return newMention(segment.WithStop(segment.Start + loc[1]))
+	}
+}
+
+func (p *hashtagParser) Parse(parent ast.Node, block text.Reader, pc parser.Context) ast.Node {
+	before := block.PrecendingCharacter()
+	line, segment := block.PeekLine()
+	s := string(line)
+
+	if !util.IsHashtagBoundary(before) {
+		return nil
+	}
+
+	for i, r := range s {
+		switch {
+		case r == '#' && i == 0:
+			continue
+		case !util.IsPermittedInHashtag(r) && !util.IsHashtagBoundary(r):
+			// Fake hashtag, don't trust it
+			return nil
+		case util.IsHashtagBoundary(r):
+			// End of hashtag
+			block.Advance(i)
+			return newHashtag(segment.WithStop(segment.Start + i))
+		}
+	}
+	// If we don't find invalid characters before the end of the line then it's good
+	block.Advance(len(s))
+	return newHashtag(segment)
+}
+
+// customRenderer fulfils both the renderer.NodeRenderer and goldmark.Extender interfaces.
+// It is created in FromMarkdown to be used a goldmark extension, and the fields are used
+// when rendering mentions and tags.
+type customRenderer struct {
+	f        *formatter
+	ctx      context.Context
+	mentions []*gtsmodel.Mention
+	tags     []*gtsmodel.Tag
+}
+
+func (r *customRenderer) RegisterFuncs(reg renderer.NodeRendererFuncRegisterer) {
+	reg.Register(kindMention, r.renderMention)
+	reg.Register(kindHashtag, r.renderHashtag)
+}
+
+func (r *customRenderer) Extend(m goldmark.Markdown) {
+	m.Parser().AddOptions(parser.WithInlineParsers(
+		// 500 is pretty arbitrary here, it was copied from example goldmark extension code.
+		// https://github.com/yuin/goldmark/blob/75d8cce5b78c7e1d5d9c4ca32c1164f0a1e57b53/extension/strikethrough.go#L111
+		mdutil.Prioritized(&mentionParser{}, 500),
+		mdutil.Prioritized(&hashtagParser{}, 500),
+	))
+	m.Renderer().AddOptions(renderer.WithNodeRenderers(
+		mdutil.Prioritized(r, 500),
+	))
+}
+
+// renderMention and renderHashtag take a mention or a hashtag ast.Node and render it as HTML.
+func (r *customRenderer) renderMention(w mdutil.BufWriter, source []byte, node ast.Node, entering bool) (ast.WalkStatus, error) {
+	if !entering {
+		return ast.WalkContinue, nil
+	}
+
+	n, ok := node.(*mention) // this function is only registered for kindMention
+	if !ok {
+		log.Errorf("type assertion failed")
+	}
+	text := string(n.Segment.Value(source))
+
+	html := r.f.ReplaceMentions(r.ctx, text, r.mentions)
+
+	// we don't have much recourse if this fails
+	if _, err := w.WriteString(html); err != nil {
+		log.Errorf("error outputting markdown text: %s", err)
+	}
+	return ast.WalkContinue, nil
+}
+
+func (r *customRenderer) renderHashtag(w mdutil.BufWriter, source []byte, node ast.Node, entering bool) (ast.WalkStatus, error) {
+	if !entering {
+		return ast.WalkContinue, nil
+	}
+
+	n, ok := node.(*hashtag) // this function is only registered for kindHashtag
+	if !ok {
+		log.Errorf("type assertion failed")
+	}
+	text := string(n.Segment.Value(source))
+
+	html := r.f.ReplaceTags(r.ctx, text, r.tags)
+
+	// we don't have much recourse if this fails
+	if _, err := w.WriteString(html); err != nil {
+		log.Errorf("error outputting markdown text: %s", err)
+	}
+	return ast.WalkContinue, nil
+}