markup: expand test coverage and sanitize notice banner output

Add previously covered autolink test cases that were dropped during the
goldmark migration (hosts without dots, https variants, single-digit
issues, cross-repo issues). Add new test suites for link rewriting with
both path-only and absolute URL prefixes, and for HTML passthrough
behavior confirming raw HTML is stripped without WithUnsafe.

Sanitize RawMarkdown output in the server notice banner to prevent
potential XSS, since it was the only call site not passing through
SanitizeBytes.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

go.mod

@@ -36,7 +36,6 @@ require (
 	github.com/olekukonko/tablewriter v1.1.3
 	github.com/pquerna/otp v1.5.0
 	github.com/prometheus/client_golang v1.23.0
-	github.com/russross/blackfriday v1.6.0
 	github.com/sergi/go-diff v1.4.0
 	github.com/sourcegraph/run v0.12.0
 	github.com/stretchr/testify v1.11.1
@@ -45,6 +44,7 @@ require (
 	github.com/unknwon/i18n v0.0.0-20190805065654-5c6446a380b6
 	github.com/unknwon/paginater v0.0.0-20170405233947-45e5d631308e
 	github.com/urfave/cli v1.22.17
+	github.com/yuin/goldmark v1.7.16
 	golang.org/x/crypto v0.47.0
 	golang.org/x/image v0.35.0
 	golang.org/x/net v0.48.0

go.sum

@@ -399,8 +399,6 @@ github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec/go.mod h1:qq
 github.com/rogpeppe/go-internal v1.9.0/go.mod h1:WtVeX8xhTBvf0smdhujwtBcq4Qrzq/fJaraNFVN+nFs=
 github.com/rogpeppe/go-internal v1.10.0 h1:TMyTOH3F/DB16zRVcYyreMH6GnZZrwQVAoYjRBZyWFQ=
 github.com/rogpeppe/go-internal v1.10.0/go.mod h1:UQnix2H7Ngw/k4C5ijL5+65zddjncjaFoBhdsK/akog=
-github.com/russross/blackfriday v1.6.0 h1:KqfZb0pUVN2lYqZUYRddxF4OR8ZMURnJIG5Y3VRLtww=
-github.com/russross/blackfriday v1.6.0/go.mod h1:ti0ldHuxg49ri4ksnFxlkCfN+hvslNlmVHqNRXXJNAY=
 github.com/russross/blackfriday/v2 v2.1.0 h1:JIOH55/0cWyOuilr9/qlrm0BSXldqnqwMsf35Ld67mk=
 github.com/russross/blackfriday/v2 v2.1.0/go.mod h1:+Rmxgy9KzJVeS9/2gXHxylqXiyQDYRxCVz55jmeOWTM=
 github.com/saintfish/chardet v0.0.0-20120816061221-3af4cd4741ca h1:NugYot0LIVPxTvN8n+Kvkn6TrbMyxQiuvKdEwFdR9vI=
@@ -457,6 +455,8 @@ github.com/urfave/cli v1.22.17 h1:SYzXoiPfQjHBbkYxbew5prZHS1TOLT3ierW8SYLqtVQ=
 github.com/urfave/cli v1.22.17/go.mod h1:b0ht0aqgH/6pBYzzxURyrM4xXNgsoT/n2ZzwQiEhNVo=
 github.com/yuin/goldmark v1.1.27/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=
 github.com/yuin/goldmark v1.2.1/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=
+github.com/yuin/goldmark v1.7.16 h1:n+CJdUxaFMiDUNnWC3dMWCIQJSkxH4uz3ZwQBkAlVNE=
+github.com/yuin/goldmark v1.7.16/go.mod h1:ip/1k0VRfGynBgxOz0yCqHrbZXhcjxyuS66Brc7iBKg=
 github.com/ziutek/mymysql v1.5.4 h1:GB0qdRGsTwQSBVYuVShFBKaXSnSnYYC2d9knnE1LHFs=
 github.com/ziutek/mymysql v1.5.4/go.mod h1:LMSpPZ6DbqWFxNCHW77HeMg9I646SAhApZ/wKdgO/C0=
 go.bobheadxi.dev/streamline v1.2.1 h1:IqKSA1TbeuDqCzYNAwtlh8sqf3tsQus8XgJdkCWFT8c=

internal/context/notice.go

@@ -54,5 +54,5 @@ func (c *Context) renderNoticeBanner() {
 		return
 	}
 
-	c.Data["ServerNotice"] = string(markup.RawMarkdown(buf, ""))
+	c.Data["ServerNotice"] = string(markup.SanitizeBytes(markup.RawMarkdown(buf, "")))
 }

internal/markup/markdown.go

@@ -3,11 +3,21 @@ package markup
 import (
 	"bytes"
 	"fmt"
+	"html"
+	"net/url"
 	"path"
 	"path/filepath"
 	"strings"
 
-	"github.com/russross/blackfriday"
+	"github.com/yuin/goldmark"
+	"github.com/yuin/goldmark/ast"
+	"github.com/yuin/goldmark/extension"
+	"github.com/yuin/goldmark/parser"
+	"github.com/yuin/goldmark/renderer"
+	goldmarkhtml "github.com/yuin/goldmark/renderer/html"
+	"github.com/yuin/goldmark/text"
+	"github.com/yuin/goldmark/util"
+	log "unknwon.dev/clog/v2"
 
 	"gogs.io/gogs/internal/conf"
 	"gogs.io/gogs/internal/lazyregexp"
@@ -25,40 +35,69 @@ func IsMarkdownFile(name string) bool {
 	return false
 }
 
-// MarkdownRenderer is a extended version of underlying Markdown render object.
-type MarkdownRenderer struct {
-	blackfriday.Renderer
-	urlPrefix string
-}
+var (
+	validLinksPattern = lazyregexp.New(`^[a-z][\w-]+://|^mailto:`)
+	linkifyURLRegexp  = lazyregexp.New(`^(?:http|https|ftp)://[-a-zA-Z0-9@:%._+~#=]{1,256}(?:\.[a-z]+)?(?::\d+)?(?:[/#?][-a-zA-Z0-9@:%_+.~#$!?&/=();,'\^{}\[\]` + "`" + `]*)?`)
+)
 
-var validLinksPattern = lazyregexp.New(`^[a-z][\w-]+://|^mailto:`)
-
-// isLink reports whether link fits valid format.
 func isLink(link []byte) bool {
 	return validLinksPattern.Match(link)
 }
 
-// Link defines how formal links should be processed to produce corresponding HTML elements.
-func (r *MarkdownRenderer) Link(out *bytes.Buffer, link, title, content []byte) {
-	if len(link) > 0 && !isLink(link) {
-		if link[0] != '#' {
-			link = []byte(path.Join(r.urlPrefix, string(link)))
-		}
-	}
-
-	r.Renderer.Link(out, link, title, content)
+type linkTransformer struct {
+	urlPrefix string
 }
 
-// AutoLink defines how auto-detected links should be processed to produce corresponding HTML elements.
-// Reference for kind: https://github.com/russross/blackfriday/blob/master/markdown.go#L69-L76
-func (r *MarkdownRenderer) AutoLink(out *bytes.Buffer, link []byte, kind int) {
-	if kind != blackfriday.LINK_TYPE_NORMAL {
-		r.Renderer.AutoLink(out, link, kind)
-		return
+func (t *linkTransformer) Transform(node *ast.Document, reader text.Reader, _ parser.Context) {
+	_ = ast.Walk(node, func(n ast.Node, entering bool) (ast.WalkStatus, error) {
+		if !entering {
+			return ast.WalkContinue, nil
+		}
+		if link, ok := n.(*ast.Link); ok {
+			dest := link.Destination
+			if len(dest) > 0 && !isLink(dest) && dest[0] != '#' {
+				link.Destination = []byte(joinURLPath(t.urlPrefix, string(dest)))
+			}
+		}
+		return ast.WalkContinue, nil
+	})
+}
+
+// joinURLPath joins a base URL prefix with a relative path. It uses net/url for
+// absolute URL prefixes to preserve the scheme and host, and path.Join for
+// path-only prefixes.
+func joinURLPath(prefix, relPath string) string {
+	u, err := url.Parse(prefix)
+	if err != nil || u.Scheme == "" {
+		return path.Join(prefix, relPath)
+	}
+	u.Path = path.Join(u.Path, relPath)
+	return u.String()
+}
+
+type gogsRenderer struct {
+	urlPrefix string
+}
+
+func (r *gogsRenderer) RegisterFuncs(reg renderer.NodeRendererFuncRegisterer) {
+	reg.Register(ast.KindAutoLink, r.renderAutoLink)
+}
+
+func (r *gogsRenderer) renderAutoLink(w util.BufWriter, source []byte, node ast.Node, entering bool) (ast.WalkStatus, error) {
+	n := node.(*ast.AutoLink)
+	if !entering {
+		return ast.WalkContinue, nil
 	}
 
-	// Since this method could only possibly serve one link at a time,
-	// we do not need to find all.
+	if n.AutoLinkType != ast.AutoLinkURL {
+		url := n.URL(source)
+		escaped := html.EscapeString(string(url))
+		_, _ = fmt.Fprintf(w, `<a href="mailto:%s">%s</a>`, escaped, escaped)
+		return ast.WalkContinue, nil
+	}
+
+	link := n.URL(source)
+
 	if bytes.HasPrefix(link, []byte(conf.Server.ExternalURL)) {
 		m := CommitPattern.Find(link)
 		if m != nil {
@@ -68,8 +107,9 @@ func (r *MarkdownRenderer) AutoLink(out *bytes.Buffer, link []byte, kind int) {
 			if j == -1 {
 				j = len(m)
 			}
-			_, _ = fmt.Fprintf(out, ` <code><a href="%s">%s</a></code>`, m, tool.ShortSHA1(string(m[i+7:j])))
-			return
+			escapedURL := html.EscapeString(string(m))
+			_, _ = fmt.Fprintf(w, ` <code><a href="%s">%s</a></code>`, escapedURL, tool.ShortSHA1(string(m[i+7:j])))
+			return ast.WalkContinue, nil
 		}
 
 		m = IssueFullPattern.Find(link)
@@ -82,78 +122,64 @@ func (r *MarkdownRenderer) AutoLink(out *bytes.Buffer, link []byte, kind int) {
 			}
 
 			index := string(m[i+7 : j])
+			escapedURL := html.EscapeString(string(m))
 			fullRepoURL := conf.Server.ExternalURL + strings.TrimPrefix(r.urlPrefix, "/")
-			var link string
+			var href string
 			if strings.HasPrefix(string(m), fullRepoURL) {
-				// Use a short issue reference if the URL refers to this repository
-				link = fmt.Sprintf(`<a href="%s">#%s</a>`, m, index)
+				href = fmt.Sprintf(`<a href="%s">#%s</a>`, escapedURL, html.EscapeString(index))
 			} else {
-				// Use a cross-repository issue reference if the URL refers to a different repository
-				repo := string(m[len(conf.Server.ExternalURL) : i-1])
-				link = fmt.Sprintf(`<a href="%s">%s#%s</a>`, m, repo, index)
+				repo := html.EscapeString(string(m[len(conf.Server.ExternalURL) : i-1]))
+				href = fmt.Sprintf(`<a href="%s">%s#%s</a>`, escapedURL, repo, html.EscapeString(index))
 			}
-			out.WriteString(link)
-			return
+			_, _ = w.WriteString(href)
+			return ast.WalkContinue, nil
 		}
 	}
 
-	r.Renderer.AutoLink(out, link, kind)
-}
-
-// ListItem defines how list items should be processed to produce corresponding HTML elements.
-func (r *MarkdownRenderer) ListItem(out *bytes.Buffer, text []byte, flags int) {
-	// Detect procedures to draw checkboxes.
-	switch {
-	case bytes.HasPrefix(text, []byte("[ ] ")):
-		text = append([]byte(`<input type="checkbox" disabled="" />`), text[3:]...)
-	case bytes.HasPrefix(text, []byte("[x] ")):
-		text = append([]byte(`<input type="checkbox" disabled="" checked="" />`), text[3:]...)
-	}
-	r.Renderer.ListItem(out, text, flags)
+	escapedLink := html.EscapeString(string(link))
+	_, _ = fmt.Fprintf(w, `<a href="%s">%s</a>`, escapedLink, escapedLink)
+	return ast.WalkContinue, nil
 }
 
 // RawMarkdown renders content in Markdown syntax to HTML without handling special links.
 func RawMarkdown(body []byte, urlPrefix string) []byte {
-	htmlFlags := 0
-	htmlFlags |= blackfriday.HTML_SKIP_STYLE
-	htmlFlags |= blackfriday.HTML_OMIT_CONTENTS
+	extensions := []goldmark.Extender{
+		extension.Table,
+		extension.Strikethrough,
+		extension.TaskList,
+		extension.NewLinkify(extension.WithLinkifyURLRegexp(linkifyURLRegexp.Regexp())),
+	}
 
 	if conf.Smartypants.Enabled {
-		htmlFlags |= blackfriday.HTML_USE_SMARTYPANTS
-		if conf.Smartypants.Fractions {
-			htmlFlags |= blackfriday.HTML_SMARTYPANTS_FRACTIONS
-		}
-		if conf.Smartypants.Dashes {
-			htmlFlags |= blackfriday.HTML_SMARTYPANTS_DASHES
-		}
-		if conf.Smartypants.LatexDashes {
-			htmlFlags |= blackfriday.HTML_SMARTYPANTS_LATEX_DASHES
-		}
-		if conf.Smartypants.AngledQuotes {
-			htmlFlags |= blackfriday.HTML_SMARTYPANTS_ANGLED_QUOTES
-		}
+		extensions = append(extensions, extension.Typographer)
 	}
 
-	renderer := &MarkdownRenderer{
-		Renderer:  blackfriday.HtmlRenderer(htmlFlags, "", ""),
-		urlPrefix: urlPrefix,
+	rendererOpts := []renderer.Option{
+		renderer.WithNodeRenderers(
+			util.Prioritized(&gogsRenderer{urlPrefix: urlPrefix}, 0),
+		),
 	}
 
-	// set up the parser
-	extensions := 0
-	extensions |= blackfriday.EXTENSION_NO_INTRA_EMPHASIS
-	extensions |= blackfriday.EXTENSION_TABLES
-	extensions |= blackfriday.EXTENSION_FENCED_CODE
-	extensions |= blackfriday.EXTENSION_AUTOLINK
-	extensions |= blackfriday.EXTENSION_STRIKETHROUGH
-	extensions |= blackfriday.EXTENSION_SPACE_HEADERS
-	extensions |= blackfriday.EXTENSION_NO_EMPTY_LINE_BEFORE_BLOCK
-
 	if conf.Markdown.EnableHardLineBreak {
-		extensions |= blackfriday.EXTENSION_HARD_LINE_BREAK
+		rendererOpts = append(rendererOpts, goldmarkhtml.WithHardWraps())
 	}
 
-	return blackfriday.Markdown(body, renderer, extensions)
+	md := goldmark.New(
+		goldmark.WithExtensions(extensions...),
+		goldmark.WithParserOptions(
+			parser.WithASTTransformers(
+				util.Prioritized(&linkTransformer{urlPrefix: urlPrefix}, 0),
+			),
+		),
+		goldmark.WithRendererOptions(rendererOpts...),
+	)
+
+	var buf bytes.Buffer
+	if err := md.Convert(body, &buf); err != nil {
+		log.Error("Failed to convert Markdown: %v", err)
+		return []byte(html.EscapeString(string(body)))
+	}
+	return buf.Bytes()
 }
 
 // Markdown takes a string or []byte and renders to HTML in Markdown syntax with special links.

internal/markup/markdown_test.go

@@ -1,11 +1,9 @@
 package markup_test
 
 import (
-	"bytes"
 	"strings"
 	"testing"
 
-	"github.com/russross/blackfriday"
 	"github.com/stretchr/testify/assert"
 
 	"gogs.io/gogs/internal/conf"
@@ -13,7 +11,9 @@ import (
 )
 
 func Test_IsMarkdownFile(t *testing.T) {
-	// TODO: Refactor to accept a list of extensions
+	oldExts := conf.Markdown.FileExtensions
+	defer func() { conf.Markdown.FileExtensions = oldExts }()
+
 	conf.Markdown.FileExtensions = strings.Split(".md,.markdown,.mdown,.mkd", ",")
 	tests := []struct {
 		ext    string
@@ -32,41 +32,152 @@ func Test_IsMarkdownFile(t *testing.T) {
 	}
 }
 
-func Test_Markdown(t *testing.T) {
-	// TODO: Refactor to accept URL
+func Test_RawMarkdown_AutoLink(t *testing.T) {
+	oldURL := conf.Server.ExternalURL
+	defer func() { conf.Server.ExternalURL = oldURL }()
+
 	conf.Server.ExternalURL = "http://localhost:3000/"
 
-	htmlFlags := 0
-	htmlFlags |= blackfriday.HTML_SKIP_STYLE
-	htmlFlags |= blackfriday.HTML_OMIT_CONTENTS
-	renderer := &MarkdownRenderer{
-		Renderer: blackfriday.HtmlRenderer(htmlFlags, "", ""),
-	}
-
 	tests := []struct {
-		input  string
-		expVal string
+		name  string
+		input string
+		want  string
 	}{
-		// Issue URL
-		{input: "http://localhost:3000/user/repo/issues/3333", expVal: "<a href=\"http://localhost:3000/user/repo/issues/3333\">#3333</a>"},
-		{input: "http://1111/2222/ssss-issues/3333?param=blah&blahh=333", expVal: "<a href=\"http://1111/2222/ssss-issues/3333?param=blah&amp;blahh=333\">http://1111/2222/ssss-issues/3333?param=blah&amp;blahh=333</a>"},
-		{input: "http://test.com/issues/33333", expVal: "<a href=\"http://test.com/issues/33333\">http://test.com/issues/33333</a>"},
-		{input: "http://test.com/issues/3", expVal: "<a href=\"http://test.com/issues/3\">http://test.com/issues/3</a>"},
-		{input: "http://issues/333", expVal: "<a href=\"http://issues/333\">http://issues/333</a>"},
-		{input: "https://issues/333", expVal: "<a href=\"https://issues/333\">https://issues/333</a>"},
-		{input: "http://tissues/0", expVal: "<a href=\"http://tissues/0\">http://tissues/0</a>"},
-
-		// Commit URL
-		{input: "http://localhost:3000/user/project/commit/d8a994ef243349f321568f9e36d5c3f444b99cae", expVal: " <code><a href=\"http://localhost:3000/user/project/commit/d8a994ef243349f321568f9e36d5c3f444b99cae\">d8a994ef24</a></code>"},
-		{input: "http://localhost:3000/user/project/commit/d8a994ef243349f321568f9e36d5c3f444b99cae#diff-2", expVal: " <code><a href=\"http://localhost:3000/user/project/commit/d8a994ef243349f321568f9e36d5c3f444b99cae#diff-2\">d8a994ef24</a></code>"},
-		{input: "https://external-link.gogs.io/gogs/gogs/commit/d8a994ef243349f321568f9e36d5c3f444b99cae#diff-2", expVal: "<a href=\"https://external-link.gogs.io/gogs/gogs/commit/d8a994ef243349f321568f9e36d5c3f444b99cae#diff-2\">https://external-link.gogs.io/gogs/gogs/commit/d8a994ef243349f321568f9e36d5c3f444b99cae#diff-2</a>"},
-		{input: "https://commit/d8a994ef243349f321568f9e36d5c3f444b99cae", expVal: "<a href=\"https://commit/d8a994ef243349f321568f9e36d5c3f444b99cae\">https://commit/d8a994ef243349f321568f9e36d5c3f444b99cae</a>"},
+		{
+			name:  "issue URL from same instance",
+			input: "http://localhost:3000/user/repo/issues/3333",
+			want:  "<p><a href=\"http://localhost:3000/user/repo/issues/3333\">#3333</a></p>\n",
+		},
+		{
+			name:  "non-matching issue-like URL",
+			input: "http://1111/2222/ssss-issues/3333?param=blah&blahh=333",
+			want:  "<p><a href=\"http://1111/2222/ssss-issues/3333?param=blah&amp;blahh=333\">http://1111/2222/ssss-issues/3333?param=blah&amp;blahh=333</a></p>\n",
+		},
+		{
+			name:  "external issue URL",
+			input: "http://test.com/issues/33333",
+			want:  "<p><a href=\"http://test.com/issues/33333\">http://test.com/issues/33333</a></p>\n",
+		},
+		{
+			name:  "commit URL from same instance",
+			input: "http://localhost:3000/user/project/commit/d8a994ef243349f321568f9e36d5c3f444b99cae",
+			want:  "<p> <code><a href=\"http://localhost:3000/user/project/commit/d8a994ef243349f321568f9e36d5c3f444b99cae\">d8a994ef24</a></code></p>\n",
+		},
+		{
+			name:  "commit URL with fragment from same instance",
+			input: "http://localhost:3000/user/project/commit/d8a994ef243349f321568f9e36d5c3f444b99cae#diff-2",
+			want:  "<p> <code><a href=\"http://localhost:3000/user/project/commit/d8a994ef243349f321568f9e36d5c3f444b99cae#diff-2\">d8a994ef24</a></code></p>\n",
+		},
+		{
+			name:  "external commit URL",
+			input: "https://external-link.gogs.io/gogs/gogs/commit/d8a994ef243349f321568f9e36d5c3f444b99cae#diff-2",
+			want:  "<p><a href=\"https://external-link.gogs.io/gogs/gogs/commit/d8a994ef243349f321568f9e36d5c3f444b99cae#diff-2\">https://external-link.gogs.io/gogs/gogs/commit/d8a994ef243349f321568f9e36d5c3f444b99cae#diff-2</a></p>\n",
+		},
+		{
+			name:  "issue URL with single digit",
+			input: "http://test.com/issues/3",
+			want:  "<p><a href=\"http://test.com/issues/3\">http://test.com/issues/3</a></p>\n",
+		},
+		{
+			name:  "host without dot in issue-like URL",
+			input: "http://issues/333",
+			want:  "<p><a href=\"http://issues/333\">http://issues/333</a></p>\n",
+		},
+		{
+			name:  "https host without dot in issue-like URL",
+			input: "https://issues/333",
+			want:  "<p><a href=\"https://issues/333\">https://issues/333</a></p>\n",
+		},
+		{
+			name:  "host without dot resembling keyword",
+			input: "http://tissues/0",
+			want:  "<p><a href=\"http://tissues/0\">http://tissues/0</a></p>\n",
+		},
+		{
+			name:  "https commit-like URL without dot",
+			input: "https://commit/d8a994ef243349f321568f9e36d5c3f444b99cae",
+			want:  "<p><a href=\"https://commit/d8a994ef243349f321568f9e36d5c3f444b99cae\">https://commit/d8a994ef243349f321568f9e36d5c3f444b99cae</a></p>\n",
+		},
 	}
 	for _, test := range tests {
-		t.Run("", func(t *testing.T) {
-			buf := new(bytes.Buffer)
-			renderer.AutoLink(buf, []byte(test.input), blackfriday.LINK_TYPE_NORMAL)
-			assert.Equal(t, test.expVal, buf.String())
+		t.Run(test.name, func(t *testing.T) {
+			got := string(RawMarkdown([]byte(test.input), ""))
+			assert.Equal(t, test.want, got)
+		})
+	}
+
+	t.Run("cross-repo issue URL from same instance", func(t *testing.T) {
+		got := string(RawMarkdown([]byte("http://localhost:3000/other/repo/issues/42"), "/user/myrepo"))
+		assert.Equal(t, "<p><a href=\"http://localhost:3000/other/repo/issues/42\">other/repo#42</a></p>\n", got)
+	})
+
+	t.Run("same-repo issue URL with fragment", func(t *testing.T) {
+		got := string(RawMarkdown([]byte("http://localhost:3000/user/myrepo/issues/42#issuecomment-1"), "/user/myrepo"))
+		assert.Equal(t, "<p><a href=\"http://localhost:3000/user/myrepo/issues/42#issuecomment-1\">#42</a></p>\n", got)
+	})
+}
+
+func Test_RawMarkdown_LinkRewriting(t *testing.T) {
+	tests := []struct {
+		name      string
+		input     string
+		urlPrefix string
+		want      string
+	}{
+		{
+			name:      "relative link with path-only prefix",
+			input:     "[text](other-file.md)",
+			urlPrefix: "/user/repo/src/branch/main",
+			want:      "<p><a href=\"/user/repo/src/branch/main/other-file.md\">text</a></p>\n",
+		},
+		{
+			name:      "relative link with absolute URL prefix",
+			input:     "[text](other-file.md)",
+			urlPrefix: "http://localhost:3000/user/repo/src/branch/main",
+			want:      "<p><a href=\"http://localhost:3000/user/repo/src/branch/main/other-file.md\">text</a></p>\n",
+		},
+		{
+			name:      "absolute link not rewritten",
+			input:     "[text](https://example.com/page)",
+			urlPrefix: "/user/repo/src/branch/main",
+			want:      "<p><a href=\"https://example.com/page\">text</a></p>\n",
+		},
+		{
+			name:      "anchor-only link not rewritten",
+			input:     "[text](#section)",
+			urlPrefix: "/user/repo/src/branch/main",
+			want:      "<p><a href=\"#section\">text</a></p>\n",
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			got := string(RawMarkdown([]byte(test.input), test.urlPrefix))
+			assert.Equal(t, test.want, got)
+		})
+	}
+}
+
+func Test_RawMarkdown_HTMLPassthrough(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		want  string
+	}{
+		{
+			name:  "inline HTML tags are stripped",
+			input: "Hello <em>world</em>",
+			want:  "<p>Hello <!-- raw HTML omitted -->world<!-- raw HTML omitted --></p>\n",
+		},
+		{
+			name:  "block HTML tags are stripped",
+			input: "<div>content</div>",
+			want:  "<!-- raw HTML omitted -->\n",
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			got := string(RawMarkdown([]byte(test.input), ""))
+			assert.Equal(t, test.want, got)
 		})
 	}
 }