Can i loop thorgh all the permission inside a list item and grant them read

[mvcsharepointdev]

I have the following list item which i am breaking its permission inheritance, but how i can loop through the current permissions (SharePoint groups, office 365 groups, single users) and grant them read-only?

  private async Task BreakRoleAsync(IListItem li)
        {
             var roleDefinitions = (await context.Web.GetAsync(p => p.RoleDefinitions)).RoleDefinitions;
            var contributeRole = roleDefinitions.AsRequested().FirstOrDefault(p => p.Name == "Contribute");
            var readRole = roleDefinitions.AsRequested().FirstOrDefault(p => p.Name == "Read");
            await li.BreakRoleInheritanceAsync(true,true);
            foreach (var r in li.RoleAssignments.AsRequested())
            {//what i need to define here??..... }




        }

Thanks