Fix html conversion of soft line breaks + rel attr for _blank link targets

Signed-off-by: Émile Ré <emile@getprobo.com>

pkg/prosemirror/html.go

@@ -198,8 +198,9 @@ func openMark(buf *bytes.Buffer, m Mark) error {
 		if attrs.Target != nil {
 			writeAttr(buf, "target", *attrs.Target)
 		}
-		if attrs.Rel != nil {
-			writeAttr(buf, "rel", *attrs.Rel)
+		rel := linkRelToEmit(attrs)
+		if rel != "" {
+			writeAttr(buf, "rel", rel)
 		}
 		if attrs.Class != nil {
 			writeAttr(buf, "class", *attrs.Class)
@@ -261,6 +262,27 @@ func renderTableCell(buf *bytes.Buffer, n Node, tag string) error {
 	return nil
 }
 
+const linkRelBlankTargetDefault = "noopener noreferrer"
+
+// linkRelToEmit returns the rel attribute value for a link mark, or empty when
+// the attribute should be omitted. When target opens a new browsing context
+// (_blank) and the document provides no rel, browsers would grant the opened
+// page access to window.opener unless noopener is set.
+func linkRelToEmit(attrs LinkAttrs) string {
+	if attrs.Rel != nil {
+		if s := strings.TrimSpace(*attrs.Rel); s != "" {
+			return s
+		}
+	}
+	if attrs.Target == nil {
+		return ""
+	}
+	if !strings.EqualFold(strings.TrimSpace(*attrs.Target), "_blank") {
+		return ""
+	}
+	return linkRelBlankTargetDefault
+}
+
 func writeAttr(buf *bytes.Buffer, name, value string) {
 	buf.WriteByte(' ')
 	buf.WriteString(name)

pkg/prosemirror/html_block.go

@@ -26,12 +26,10 @@ import (
 
 // htmlBlockSanitizePolicy matches tags and attributes we can represent as
 // ProseMirror/Tiptap JSON and strips scripts, event handlers, and unsafe URLs.
-func htmlBlockSanitizePolicy() *bluemonday.Policy {
-	return bluemonday.UGCPolicy()
-}
+var htmlBlockSanitizePolicy = bluemonday.UGCPolicy()
 
 func sanitizeHTMLBlockContent(s string) string {
-	return htmlBlockSanitizePolicy().Sanitize(s)
+	return htmlBlockSanitizePolicy.Sanitize(s)
 }
 
 // convertProseMirrorFromInlineHTML sanitizes inline raw HTML and maps it to

pkg/prosemirror/html_test.go

@@ -187,6 +187,45 @@ func TestRenderHTML_LinkMinimalAttrs(t *testing.T) {
 	assert.Equal(t, `<a href="https://example.com">hi</a>`, got)
 }
 
+func TestRenderHTML_LinkBlankTargetDefaultRel(t *testing.T) {
+	t.Parallel()
+
+	for _, tc := range []struct {
+		name string
+		raw  string
+		want string
+	}{
+		{
+			name: "no rel",
+			raw:  `{"type":"text","marks":[{"type":"link","attrs":{"href":"https://example.com","target":"_blank","rel":null}}],"text":"hi"}`,
+			want: `<a href="https://example.com" target="_blank" rel="noopener noreferrer">hi</a>`,
+		},
+		{
+			name: "case insensitive target",
+			raw:  `{"type":"text","marks":[{"type":"link","attrs":{"href":"https://example.com","target":"_BLANK"}}],"text":"hi"}`,
+			want: `<a href="https://example.com" target="_BLANK" rel="noopener noreferrer">hi</a>`,
+		},
+		{
+			name: "whitespace rel treated as absent",
+			raw:  `{"type":"text","marks":[{"type":"link","attrs":{"href":"https://example.com","target":" _blank ","rel":"  "}}],"text":"hi"}`,
+			want: `<a href="https://example.com" target=" _blank " rel="noopener noreferrer">hi</a>`,
+		},
+	} {
+		t.Run(
+			tc.name,
+			func(t *testing.T) {
+				t.Parallel()
+				var n Node
+				require.NoError(t, json.Unmarshal([]byte(tc.raw), &n))
+
+				got, err := RenderHTML(n)
+				require.NoError(t, err)
+				assert.Equal(t, tc.want, got)
+			},
+		)
+	}
+}
+
 func TestRenderHTML_LinkSanitizesDangerousHrefs(t *testing.T) {
 	t.Parallel()
 

pkg/prosemirror/markdown.go

@@ -117,6 +117,9 @@ func (c *converter) collectRawHTMLRun(start ast.Node) (run string, next ast.Node
 		case ast.KindText:
 			t := ch.(*ast.Text)
 			buf.Write(t.Segment.Value(c.source))
+			if t.SoftLineBreak() {
+				buf.WriteByte(' ')
+			}
 		case ast.KindString:
 			buf.Write(ch.(*ast.String).Value)
 		default:
@@ -352,6 +355,9 @@ func (c *converter) convertImage(n *ast.Image) ([]Node, error) {
 
 func (c *converter) convertText(n *ast.Text) ([]Node, error) {
 	content := string(n.Segment.Value(c.source))
+	if n.SoftLineBreak() {
+		content += " "
+	}
 	if content == "" {
 		return nil, nil
 	}

pkg/prosemirror/markdown_test.go

@@ -16,6 +16,7 @@ package prosemirror
 
 import (
 	"encoding/json"
+	"strings"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -351,6 +352,25 @@ func TestParseMarkdown_HardBreak(t *testing.T) {
 	assert.True(t, hasHardBreak, "expected hard break node")
 }
 
+func TestParseMarkdown_SoftLineBreak(t *testing.T) {
+	t.Parallel()
+
+	doc, err := ParseMarkdown("line one\nand line two")
+	require.NoError(t, err)
+	require.Len(t, doc.Content, 1)
+
+	p := doc.Content[0]
+	require.Equal(t, NodeParagraph, p.Type)
+
+	var joined strings.Builder
+	for _, child := range p.Content {
+		if child.Type == NodeText && child.Text != nil {
+			joined.WriteString(*child.Text)
+		}
+	}
+	assert.Equal(t, "line one and line two", joined.String())
+}
+
 func TestParseMarkdown_NestedMarks(t *testing.T) {
 	t.Parallel()