我正在尝试将boost::beast::websocket::stream<T>
(针对2个特定的T
)包装在中,boost::variant
以允许将TLS([T = boost::asio::ssl::stream<boost::asio::ip::tcp::socket>]
)和非TLS([T = boost::asio::ip::tcp::socket]
)websocket视为相同。我被编译失败卡住了。
我能想到的最简单的失败示例是:
#include <boost/asio/ssl.hpp>
#include <boost/beast/core.hpp>
#include <boost/beast/websocket.hpp>
#include <boost/variant.hpp>
using tcp = boost::asio::ip::tcp;
namespace ws = boost::beast::websocket;
namespace ssl = boost::asio::ssl;
using base_ws = boost::variant<
ws::stream<tcp::socket>, ws::stream<ssl::stream<tcp::socket>>>;
class test
{
public:
static void init( tcp::socket && socket )
{
ssl::context ctx{ ssl::context::tlsv12_server };
ws::stream<ssl::stream<tcp::socket>> s{ std::move( socket ), ctx };
base_ws{ std::move( s ) };
}
};
int main()
{}
编译失败并报错:
In file included from /server/src/ws_server.cpp:9:
In file included from /include/boost/beast/websocket.hpp:18:
In file included from /include/boost/beast/websocket/stream.hpp:3455:
/include/boost/beast/websocket/impl/stream.ipp:47:7: error: no matching constructor for initialization of 'boost::asio::ssl::stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp> >'
: stream_(std::forward<Args>(args)...)
^ ~~~~~~~~~~~~~~~~~~~~~~~~
/include/boost/variant/detail/initializer.hpp:122:27: note: in instantiation of function template specialization 'boost::beast::websocket::stream<boost::asio::ssl::stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp> > >::stream<boost::beast::websocket::stream<boost::asio::ssl::stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp> > > >' requested here
new(dest) value_T( boost::detail::variant::move(operand) );
^
/include/boost/variant/variant.hpp:1687:28: note: in instantiation of member function 'boost::detail::variant::make_initializer_node::apply<boost::mpl::pair<boost::detail::variant::make_initializer_node::apply<boost::mpl::pair<boost::detail::variant::initializer_root, mpl_::int_<0> >, boost::mpl::l_iter<boost::mpl::list2<boost::beast::websocket::stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp> >, boost::beast::websocket::stream<boost::asio::ssl::stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp> > > > > >::initializer_node, mpl_::int_<1> >, boost::mpl::l_iter<boost::mpl::list1<boost::beast::websocket::stream<boost::asio::ssl::stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp> > > > > >::initializer_node::initialize' requested here
initializer::initialize(
^
/include/boost/variant/variant.hpp:1858:9: note: in instantiation of function template specialization 'boost::variant<boost::beast::websocket::stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp> >, boost::beast::websocket::stream<boost::asio::ssl::stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp> > > >::convert_construct<boost::beast::websocket::stream<boost::asio::ssl::stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp> > > >' requested here
convert_construct( detail::variant::move(operand), 1L);
^
/server/src/ws_server.cpp:372:20: note: in instantiation of function template specialization 'boost::variant<boost::beast::websocket::stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp> >, boost::beast::websocket::stream<boost::asio::ssl::stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp> > > >::variant<boost::beast::websocket::stream<boost::asio::ssl::stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp> > > >' requested here
return base_ws( std::move( s ) );
^
/include/boost/asio/ssl/stream.hpp:64:7: note: candidate constructor (the implicit copy constructor) not viable: no known conversion from 'boost::beast::websocket::stream<boost::asio::ssl::stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp> > >' to 'const boost::asio::ssl::stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp> >' for 1st argument
class stream :
^
/include/boost/asio/ssl/stream.hpp:98:3: note: candidate constructor template not viable: requires 2 arguments, but 1 was provided
stream(Arg&& arg, context& ctx)
^
我会提供Godbolt,但是超时了,coliru不提供所需的openssl boost/asio/ssl.hpp
。
每这里,boost::variant
应该接受T &&
并使用它来实例化T
内部。
每这里,boost::beast::websocket::stream
确实有一个移动构造函数。
move构造函数是更具体的,那么编译器为什么要stream<...>
如第一个注释中所述选择可变参数的构造函数()?
boost::beast::websocket::stream<
boost::asio::ssl::stream<
boost::asio::basic_stream_socket<boost::asio::ip::tcp>
>
>::stream<
boost::beast::websocket::stream<
boost::asio::ssl::stream<
boost::asio::basic_stream_socket<boost::asio::ip::tcp>
>
>
>
我正在使用Boost 1.66.0和Clang 7。
我忽略的关键信息在以下描述中boost::beast::websocket::stream::stream(stream&&)
:
如果
NextLayer
可移动构造,则此功能将从现有流中移动构造一个新流。
事实证明,该boost::asio::ssl::stream
动作不可构造,因此stream
未生成默认的move构造函数。ssl::stream
在chriskohlhoff / asio#124中有一个开放的问题可以使动作可构造,其中引用了boost bugtracker。
然后,解决该问题的方法是使用可移动构造的实现ssl::stream
,例如此处Beast示例中提供的实现,看起来它可能boost/beast/experimental/core/ssl_stream.hpp
在更高版本的Beast中可用(不在1.67.0中提供)。
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