From 1e4117f1e1830723ae5d15cc7876370de14bf645 Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Sat, 1 Jan 2022 16:19:51 +0100
Subject: [PATCH] LibCore: Add syscall wrapper for getgroups()

This wrapper does all the grunt work of figuring out how many extra GIDs
there are, and then returning them nicely wrapped in a Vector<gid_t>.
---
 Userland/Libraries/LibCore/System.cpp | 17 ++++++++++++++++-
 Userland/Libraries/LibCore/System.h   |  2 +-
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/Userland/Libraries/LibCore/System.cpp b/Userland/Libraries/LibCore/System.cpp
index 92ab111dcd..37cca47260 100644
--- a/Userland/Libraries/LibCore/System.cpp
+++ b/Userland/Libraries/LibCore/System.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2021-2022, Andreas Kling <kling@serenityos.org>
  * Copyright (c) 2021, Kenneth Myhra <kennethmyhra@gmail.com>
  * Copyright (c) 2021, Sam Atkins <atkinssj@serenityos.org>
  *
@@ -7,6 +7,7 @@
  */
 
 #include <AK/String.h>
+#include <AK/Vector.h>
 #include <LibCore/System.h>
 #include <LibSystem/syscall.h>
 #include <stdarg.h>
@@ -742,4 +743,18 @@ ErrorOr<Array<int, 2>> pipe2([[maybe_unused]] int flags)
     return fds;
 }
 
+ErrorOr<Vector<gid_t>> getgroups()
+{
+    int count = ::getgroups(0, nullptr);
+    if (count < 0)
+        return Error::from_syscall("getgroups"sv, -errno);
+    if (count == 0)
+        return Vector<gid_t> {};
+    Vector<gid_t> groups;
+    TRY(groups.try_resize(count));
+    if (::getgroups(count, groups.data()) < 0)
+        return Error::from_syscall("getgroups"sv, -errno);
+    return groups;
+}
+
 }
diff --git a/Userland/Libraries/LibCore/System.h b/Userland/Libraries/LibCore/System.h
index d30457b495..1353108885 100644
--- a/Userland/Libraries/LibCore/System.h
+++ b/Userland/Libraries/LibCore/System.h
@@ -105,5 +105,5 @@ ErrorOr<void> setsockopt(int sockfd, int level, int option, void const* value, s
 ErrorOr<void> getsockname(int sockfd, struct sockaddr*, socklen_t*);
 ErrorOr<void> getpeername(int sockfd, struct sockaddr*, socklen_t*);
 ErrorOr<void> socketpair(int domain, int type, int protocol, int sv[2]);
-
+ErrorOr<Vector<gid_t>> getgroups();
 }