randomSecure

fn randomSecure(userdata: ?*anyopaque, buffer: []u8) Io.RandomSecureError!void {
    const ev: *Evented = @ptrCast(@alignCast(userdata));
    if (buffer.len == 0) return;
    var cancel_region: CancelRegion = .init();
    defer cancel_region.deinit();
    ev.urandomReadAll(&cancel_region, buffer) catch |err| switch (err) {
        error.Canceled => |e| return e,
        else => return error.EntropyUnavailable,
    };
}