From 0bd8aa72e29ec353a6351bb5b99d2d5c8bfc0fb0 Mon Sep 17 00:00:00 2001
From: Charlie Gordon <github@chqrlie.org>
Date: Thu, 9 May 2024 23:29:57 +0200
Subject: [PATCH] Improve `js_os_exec`

- Try and use `closefrom()` if available
- limit the fallback loop to 1024 handles to avoid
  costly loop on linux alpine.
PR inspired by @nicolas-duteil-nova
---
 Makefile                |  5 +++++
 compat/test-closefrom.c |  6 ++++++
 quickjs-libc.c          | 26 ++++++++++++++++++++++----
 3 files changed, 33 insertions(+), 4 deletions(-)
 create mode 100644 compat/test-closefrom.c

diff --git a/Makefile b/Makefile
index be0ff471a..c84bc44f2 100644
--- a/Makefile
+++ b/Makefile
@@ -143,6 +143,11 @@ endif
 ifdef CONFIG_WIN32
 DEFINES+=-D__USE_MINGW_ANSI_STDIO # for standard snprintf behavior
 endif
+ifndef CONFIG_WIN32
+ifeq ($(shell $(CC) -o /dev/null compat/test-closefrom.c 2>/dev/null && echo 1),1)
+DEFINES+=-DHAVE_CLOSEFROM
+endif
+endif
 
 CFLAGS+=$(DEFINES)
 CFLAGS_DEBUG=$(CFLAGS) -O0
diff --git a/compat/test-closefrom.c b/compat/test-closefrom.c
new file mode 100644
index 000000000..1324e97bf
--- /dev/null
+++ b/compat/test-closefrom.c
@@ -0,0 +1,6 @@
+#include <unistd.h>
+
+int main(void) {
+    closefrom(3);
+    return 0;
+}
diff --git a/quickjs-libc.c b/quickjs-libc.c
index dd9f55f14..81371507f 100644
--- a/quickjs-libc.c
+++ b/quickjs-libc.c
@@ -3015,7 +3015,6 @@ static JSValue js_os_exec(JSContext *ctx, JSValueConst this_val,
     }
     if (pid == 0) {
         /* child */
-        int fd_max = sysconf(_SC_OPEN_MAX);
 
         /* remap the stdin/stdout/stderr handles if necessary */
         for(i = 0; i < 3; i++) {
@@ -3024,9 +3023,28 @@ static JSValue js_os_exec(JSContext *ctx, JSValueConst this_val,
                     _exit(127);
             }
         }
-
-        for(i = 3; i < fd_max; i++)
-            close(i);
+#if defined(HAVE_CLOSEFROM)
+        /* closefrom() is available on many recent unix systems:
+           Linux with glibc 2.34+, Solaris 9+, FreeBSD 7.3+,
+           NetBSD 3.0+, OpenBSD 3.5+.
+           Linux with the musl libc and macOS don't have it.
+         */
+
+        closefrom(3);
+#else
+        {
+            /* Close the file handles manually, limit to 1024 to avoid
+               costly loop on linux Alpine where sysconf(_SC_OPEN_MAX)
+               returns a huge value 1048576.
+               Patch inspired by nicolas-duteil-nova. See also:
+               https://stackoverflow.com/questions/73229353/
+               https://stackoverflow.com/questions/899038/#918469
+             */
+            int fd_max = min_int(sysconf(_SC_OPEN_MAX), 1024);
+            for(i = 3; i < fd_max; i++)
+                close(i);
+        }
+#endif
         if (cwd) {
             if (chdir(cwd) < 0)
                 _exit(127);