From 19b0292e4bb88f8ab91aa84595d79aa790e64e5f Mon Sep 17 00:00:00 2001
From: Bryce Kwon <bryce@brycekwon.com>
Date: Fri, 16 Oct 2026 22:20:33 -1000
Subject: Let a Lua script write while it loads

A script's top level runs before cgit hooks stdout for it, and the
unhook html() began with tripped an assert that aborted cgit.
---
 source/filter.c        |  8 ++++++--
 tests/t0201-filters.sh | 20 ++++++++++++++++++++
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/source/filter.c b/source/filter.c
index ec48007..b36f03e 100644
--- a/source/filter.c
+++ b/source/filter.c
@@ -225,15 +225,19 @@ static inline int emit_unfiltered(lua_State *lua_state, void (*emit)(const char
 	if (!text)
 		return 0;
 
+	// A script that writes while it is still loading runs before cgit has
+	// hooked stdout for it, so there is no hook to take off.
 	saved_write = filter_write;
 	saved_filter = current_write_filter;
-	unhook_write();
+	if (saved_write)
+		unhook_write();
 	emit(text);
 	// emit leaves bytes in the html buffer, so empty it while the hook is
 	// still off. Re-hooking first would send the page's own bytes back into
 	// the filter.
 	html_flush();
-	hook_write(saved_filter, saved_write);
+	if (saved_write)
+		hook_write(saved_filter, saved_write);
 
 	return 0;
 }
diff --git a/tests/t0201-filters.sh b/tests/t0201-filters.sh
index 1dd0910..c2d0ec4 100755
--- a/tests/t0201-filters.sh
+++ b/tests/t0201-filters.sh
@@ -130,4 +130,24 @@ test_expect_success CGIT_LUA 'a failing lua filter still renders an error page'
 	grep "Lua error in" err
 '
 
+# A script runs its top level before cgit hooks stdout for it, so what it
+# writes there goes straight onto the page instead of tripping the hook.
+test_expect_success CGIT_LUA 'a lua filter that writes while loading still renders' '
+	cat >loud.lua <<-\EOF &&
+	html("written while loading")
+	function filter_open(...) end
+	function filter_write(str) html(str) end
+	function filter_close() return 0 end
+	EOF
+	{
+		echo "cache-size=0" &&
+		echo "repo.url=foo" &&
+		echo "repo.path=$PWD/repos/foo/.git" &&
+		echo "repo.commit-filter=lua:$PWD/loud.lua"
+	} >loudrc &&
+	CGIT_CONFIG="$PWD/loudrc" QUERY_STRING="url=foo/commit" cgit >tmp &&
+	grep "written while loading" tmp &&
+	grep "</html>" tmp
+'
+
 test_done
-- 
cgit