Render README markdown in the browser

cgit had no markdown support of its own, so a readme was rendered
through an external python filter or not at all. Escaping the source
and formatting it in cgit.js keeps the work in the browser like the
blob highlighter, and the page stays readable as plain text without
scripting.

1 file changed, 39 insertions, 9 deletions

diff --git a/source/ui-summary.c b/source/ui-summary.c
index 947812a..7e533e1 100644
--- a/source/ui-summary.c
+++ b/source/ui-summary.c
@@ -99,6 +99,17 @@ static char* append_readme_path(const char *filename, const char *ref, const cha
 	return full_path;
 }
 
+static int readme_is_markdown(const char *filename)
+{
+	const char *ext = strrchr(filename, '.');
+
+	if (!ext || !ext[1])
+		return 0;
+	ext++;
+	return !strcasecmp(ext, "md") || !strcasecmp(ext, "markdown") ||
+	       !strcasecmp(ext, "mkd") || !strcasecmp(ext, "mdown");
+}
+
 void cgit_print_repo_readme(const char *path)
 {
 	char *filename, *ref, *mimetype;
@@ -128,16 +139,35 @@ void cgit_print_repo_readme(const char *path)
 			goto done;
 	}
 
-	/* Print the calculated readme, either from the git repo or from the
-	 * filesystem, while applying the about-filter.
-	 */
 	html("<div id='summary'>");
-	cgit_open_filter(ctx.repo->about_filter, filename);
-	if (ref)
-		cgit_print_file(filename, ref, 1);
-	else
-		html_include(filename);
-	cgit_close_filter(ctx.repo->about_filter);
+	if (!ctx.repo->about_filter && ctx.cfg.enable_markdown &&
+	    readme_is_markdown(filename)) {
+		/* No about-filter is set, so hand the markdown source to the
+		 * built-in client-side renderer in cgit.js. The source is
+		 * escaped here and rendered in the browser, and it degrades to
+		 * readable plain text when scripting is off.
+		 */
+		html("<div class='markdown' data-markdown>");
+		if (ref) {
+			cgit_print_file(filename, ref, 1, 1);
+		} else {
+			struct strbuf sb = STRBUF_INIT;
+			if (strbuf_read_file(&sb, filename, 0) >= 0)
+				html_txt(sb.buf);
+			strbuf_release(&sb);
+		}
+		html("</div>");
+	} else {
+		/* Otherwise print the readme through the about-filter, or raw
+		 * when none is configured.
+		 */
+		cgit_open_filter(ctx.repo->about_filter, filename);
+		if (ref)
+			cgit_print_file(filename, ref, 1, 0);
+		else
+			html_include(filename);
+		cgit_close_filter(ctx.repo->about_filter);
+	}
 
 	html("</div>");
 	if (free_filename)