LibCore: Add query for all accounts and groups

Author: https://github.com/ne0ndrag0n
Commit: 9ddb86f7db
Pull-request: https://github.com/SerenityOS/serenity/pull/15965
Reviewed-by: https://github.com/ADKaster ✅
Reviewed-by: https://github.com/FireFox317
Reviewed-by: https://github.com/awesomekling

Userland/Libraries/LibCore/Group.cpp

@@ -6,8 +6,10 @@
 
 #include <AK/CharacterTypes.h>
 #include <AK/ScopeGuard.h>
+#include <LibCore/File.h>
 #include <LibCore/Group.h>
 #include <LibCore/System.h>
+#include <errno.h>
 
 namespace Core {
 
@@ -60,6 +62,27 @@ ErrorOr<void> Group::add_group(Group& group)
 }
 #endif
 
+ErrorOr<Vector<Group>> Group::all()
+{
+    Vector<Group> groups;
+
+    ScopeGuard grent_guard([] { endgrent(); });
+    setgrent();
+    errno = 0;
+    for (auto const* gr = getgrent(); gr; gr = getgrent()) {
+        Vector<String> members;
+        for (size_t i = 0; gr->gr_mem[i]; ++i)
+            members.append(*gr->gr_mem);
+
+        groups.append({ gr->gr_name, gr->gr_gid, members });
+    }
+
+    if (errno)
+        return Error::from_errno(errno);
+
+    return groups;
+}
+
 Group::Group(String name, gid_t id, Vector<String> members)
     : m_name(move(name))
     , m_id(id)