Hi,

Right now gotwebd already finds README/README.md/README.txt <http://README.md/README.txt> in arepo's top-level tree (got_output_repo_tree() in got_operations.c)and shows the first match under the file listing on the tree page.The problem is that it's dumped through tp_write_htmlescape() into a<pre> block, so Markdown syntax (#, **, links, lists, etc.) shows upliterally instead of being rendered — unlike GitHub, GitLab, Gitea,or even cgit's "about" page.

This patch adds got_render_readme_markdown(), a small wrapper aroundlowdown_buf(3) from textproc/lowdown (already a port, ISC/BSDlicensed, no external dependencies, and explicitly designed to workunder pledge(2) per lowdown(3) — it doesn't need any promise beyondwhat gotwebd's fcgi process already has). Only files ending in .mdgo through this path; plain README and README.txt keep being shownexactly as before, escaped inside <pre>.

Since README content comes from repository data and not from thegotwebd operator, LOWDOWN_HTML_OWASP is enabled so any raw HTMLembedded in the Markdown gets sanitized rather than passed throughas-is.

Also adds a small .readme block to gotweb.css so headings, codeblocks, tables and blockquotes inside the rendered README don't lookout of place next to the rest of the page.

Thanks
diff --git a/gotwebd/files/htdocs/gotwebd/gotweb.css b/gotwebd/files/htdocs/gotwebd/gotweb.css
index de0fc45..4b0ae1d 100755
--- a/gotwebd/files/htdocs/gotwebd/gotweb.css
+++ b/gotwebd/files/htdocs/gotwebd/gotweb.css
@@ -382,6 +382,38 @@ header.subtitle h2 {
 	margin-bottom: 20px;
 	border-collapse: collapse;
 }
+.readme {
+	max-width: 900px;
+	line-height: 1.5;
+	padding: 1em 0;
+}
+.readme h1, .readme h2, .readme h3 {
+	border-bottom: 1px solid LightSlateGray;
+	padding-bottom: 0.2em;
+}
+.readme pre {
+	background-color: #f6f6f6;
+	padding: 0.5em;
+	overflow-x: auto;
+}
+.readme code {
+	font-family: monospace;
+	background-color: #f6f6f6;
+	padding: 0.1em 0.3em;
+}
+.readme table {
+	border-collapse: collapse;
+}
+.readme th, .readme td {
+	border: 1px solid LightSlateGray;
+	padding: 0.3em 0.6em;
+}
+.readme blockquote {
+	border-left: 3px solid LightSlateGray;
+	margin-left: 0;
+	padding-left: 1em;
+	color: #555;
+}
 .tree_wrapper:nth-child(odd) {
 	background-color: #d8f3ef;
 }
diff --git a/gotwebd/got_operations.c b/gotwebd/got_operations.c
index 68e9ef0..5f0ac3a 100644
--- a/gotwebd/got_operations.c
+++ b/gotwebd/got_operations.c
@@ -28,6 +28,8 @@
 #include <string.h>
 #include <unistd.h>
 
+#include <lowdown.h>
+
 #include "got_error.h"
 #include "got_object.h"
 #include "got_reference.h"
@@ -760,6 +762,62 @@ got_output_repo_tree(struct request *c, char **readme,
 	return 0;
 }
 
+/*
+ * Render a Markdown README (buf/len) into a sanitized HTML5 fragment,
+ * the same way GitHub renders README.md on a repository's front page.
+ * Returns 0 and a NUL-terminated *html on success, -1 on failure.
+ * The caller must free *html.
+ */
+int
+got_render_readme_markdown(char **html, const uint8_t *buf, size_t len)
+{
+	struct lowdown_opts opts;
+	char *out = NULL;
+	size_t outlen = 0;
+
+	*html = NULL;
+
+	memset(&opts, 0, sizeof(opts));
+	opts.type = LOWDOWN_HTML;
+	opts.feat = LOWDOWN_AUTOLINK | LOWDOWN_TABLES | LOWDOWN_FENCED |
+	    LOWDOWN_STRIKE | LOWDOWN_SUPER | LOWDOWN_COMMONMARK |
+	    LOWDOWN_DEFLIST | LOWDOWN_ATTRS;
+	/*
+	 * OWASP-sanitize any raw HTML embedded in the README: this content
+	 * comes from repository data which gotwebd must not trust blindly.
+	 */
+	opts.oflags = LOWDOWN_HTML_HEAD_IDS | LOWDOWN_HTML_NUM_ENT |
+	    LOWDOWN_HTML_OWASP | LOWDOWN_SMARTY;
+
+	if (!lowdown_buf(&opts, (const char *)buf, len, &out, &outlen, NULL))
+		return -1;
+
+	/* lowdown_buf() does not guarantee NUL-termination. */
+	*html = malloc(outlen + 1);
+	if (*html == NULL) {
+		free(out);
+		return -1;
+	}
+	memcpy(*html, out, outlen);
+	(*html)[outlen] = '\0';
+	free(out);
+	return 0;
+}
+
+/*
+ * Return non-zero if the given README file name should be rendered as
+ * Markdown (case-insensitive ".md" suffix), matching GitHub's convention.
+ */
+int
+got_readme_is_markdown(const char *name)
+{
+	size_t len = strlen(name);
+
+	if (len < 3)
+		return 0;
+	return strcasecmp(name + len - 3, ".md") == 0;
+}
+
 const struct got_error *
 got_open_blob_for_output(struct got_blob_object **blob, int *fd,
     int *binary, struct request *c, const char *directory, const char *file,
diff --git a/gotwebd/gotwebd.h b/gotwebd/gotwebd.h
index 09387b7..adcf4ba 100644
--- a/gotwebd/gotwebd.h
+++ b/gotwebd/gotwebd.h
@@ -703,6 +703,8 @@ const struct got_error *got_get_repo_heads(struct request *);
 const struct got_error *got_open_diff_for_output(FILE **, struct request *);
 int got_output_repo_tree(struct request *, char **,
     int (*)(struct template *, struct got_tree_entry *));
+int got_render_readme_markdown(char **, const uint8_t *, size_t);
+int got_readme_is_markdown(const char *);
 const struct got_error *got_open_blob_for_output(struct got_blob_object **,
     int *, int *, struct request *, const char *, const char *, const char *);
 int got_output_blob_by_lines(struct template *, struct got_blob_object *,
diff --git a/gotwebd/pages.tmpl b/gotwebd/pages.tmpl
index a148101..26560ac 100644
--- a/gotwebd/pages.tmpl
+++ b/gotwebd/pages.tmpl
@@ -737,7 +737,11 @@ nextsep(char *s, char **t)
 	const struct querystring *qs = c->t->qs;
 	struct gotweb_url	 url;
 	char			*readme = NULL;
+	char			*readme_buf = NULL;
+	char			*readme_html = NULL;
+	size_t			 readme_bufsz = 0;
 	int			 binary;
+	int			 is_markdown = 0;
 	const uint8_t		*buf;
 	size_t			 len;
 !}
@@ -746,6 +750,8 @@ nextsep(char *s, char **t)
   </table>
   {{ if readme }}
     {!
+	is_markdown = got_readme_is_markdown(readme);
+
 	error = got_open_blob_for_output(&t->blob, &t->fd, &binary, c,
 	    qs->folder[0] ? qs->folder : NULL, readme,
 	    qs->commit[0] ? qs->commit : NULL);
@@ -768,6 +774,47 @@ nextsep(char *s, char **t)
           {{ readme }}
         </a>
       </h2>
+      {{ if is_markdown }}
+        {!
+		/* Slurp the blob so lowdown can parse it as one buffer. */
+		for (;;) {
+			char *tmp;
+
+			error = got_object_blob_read_block(&len, t->blob);
+			if (error) {
+				free(readme);
+				free(readme_buf);
+				return (-1);
+			}
+			if (len == 0)
+				break;
+			buf = got_object_blob_get_read_buf(t->blob);
+			tmp = realloc(readme_buf, readme_bufsz + len);
+			if (tmp == NULL) {
+				free(readme);
+				free(readme_buf);
+				return (-1);
+			}
+			readme_buf = tmp;
+			memcpy(readme_buf + readme_bufsz, buf, len);
+			readme_bufsz += len;
+		}
+		if (got_render_readme_markdown(&readme_html,
+		    (uint8_t *)readme_buf, readme_bufsz) == -1) {
+			free(readme);
+			free(readme_buf);
+			return (-1);
+		}
+        !}
+      <div class="readme markdown-body">
+        {! if (tp_write(tp, readme_html, strlen(readme_html)) == -1) {
+			free(readme);
+			free(readme_buf);
+			free(readme_html);
+			return (-1);
+		} !}
+      </div>
+      {{ else }}
       <pre>
         {!
 		for (;;) {
@@ -786,10 +833,15 @@ nextsep(char *s, char **t)
 		}
         !}
       </pre>
+      {{ end }}
     {{ end }}
   {{ end }}
 {{ finally }}
-  {! free(readme); !}
+  {!
+	free(readme);
+	free(readme_buf);
+	free(readme_html);
+  !}
 {{ end }}
 
 {{ define gotweb_render_tree(struct template *tp) }}

Index: gotwebd/Makefile
===================================================================
--- gotwebd/Makefile
+++ gotwebd/Makefile
@@ -30,7 +30,7 @@
 MAN =		${PROG}.conf.5 ${PROG}.8
 CPPFLAGS +=	-I${.CURDIR}/../include -I${.CURDIR}/../lib -I${.CURDIR}
 CPPFLAGS +=	-I${.CURDIR}/../template
-LDADD +=	-lz -levent -lutil -lm -lcrypto
+LDADD +=	-lz -levent -lutil -lm -lcrypto -llowdown
 YFLAGS =
 DPADD =		${LIBEVENT} ${LIBUTIL} ${LIBM} ${LIBCRYPTO}
 #CFLAGS +=	-DGOT_NO_OBJ_CACHE

• gotwebd-readme-markdown.patch (6K)