Set the maximum incoming message size option.

void
read_message_max(
    std::size_t amount);

Sets the largest permissible incoming message size. Message frame fields indicating a size that would bring the total message size over this limit will cause a protocol failure. The default setting is 16 megabytes. A value of zero indicates a limit of the maximum value of a std::uint64_t.

Setting the maximum read message size.

ws.read_message_max(65536);