Beast: websocket-server-async crash when modify __ws__.async_write(boost::asio::buffer(std::string("1234567890"), ....))

[weiweiloong]

hello,
when l learn websocket how to use the demo of websocket-server-async;
version:
boost_1_66_0\boost\beast\websocket
i only modeify __ws__.async_write(.........), and my code like this in the demo project "websocket-server-async";
{
。。。。。
namespace websocket = boost::beast::websocket;
websocket::stream __ws__;
boost::asio::strand strand_;
boost::beast::multi_buffer buffer_;

//__ws__.async_write( buffer_.data(), boost::asio::bind_executor( strand_, std::bind( &session::on_write, //shared_from_this(), std::placeholders::_1, std::placeholders::_2)));

__ws__.async_write( boost::asio::buffer(std::string("1234567890")), boost::asio::bind_executor( strand_, std::bind( &session::on_write, shared_from_this(), std::placeholders::_1, std::placeholders::_2)));
}
but the code is breakdown after i modify the code as __ws__.async_write(boost::asio::buffer(std::string("1234567890"), ....)); when server recive information from websocket client;

[vinniefalco]

You are constructing the temporary string std::string("1234567890") and passing that as a parameter to async_write. When the string is destroyed, the asynchronous operation will produce an access violation. You need to make sure the string exists until at least the completion handler is invoked:

auto sp = std::make_shared<std::string>("1234567890");
ws.async_write(
    boost::asio::buffer(*sp), boost::asio::bind_executor(strand_,
    [sp, self=shared_from_this()](boost::beast::error_code ec, std::size_t bytes_transferred)
    {
        self->on_write(ec, bytes_transferred);
    }));

[weiweiloong]

tks

[vinniefalco]

Has this issue been resolved?

[IESBMNT]

I’m doing something similar. I’ve adapted the example at https://www.boost.org/doc/libs/develop/libs/beast/example/websocket/server/async/websocket_server_async.cpp.

I’m attempting to write asynchronously to websockets while they are open. In class Session I’ve added the following.

//Send a message to the client
void Session::SendMessage(std::string& message)
{
    ws_.async_write(boost::asio::buffer(message), beast::bind_front_handler(&Session::OnWrite, writeString));
   //Race condition if message is deallocated/reused/mutated
}

How can I deallocate the message string on successful write? The provided Listener class uses .async_accept() to construct the Session, and does not seem to provide a way to reference the associated strand for use with bind_executor as in the answer above. With the current composed example I have no way to manage the lifetime of the message object, and it must be guaranteed to exist until write. Perhaps this is not idiomatic websocket use in beast?

[vinniefalco]

Make a small reference counted, lightweight copyable container that meets the requirements of _ConstBufferSequence_ and pass that as the buffer. Something like this:
https://github.com/vinniefalco/BeastLounge/blob/7be4bcf47c98c6bfd97ef3e0906c1dce0fd5ce75/server/message.hpp#L22

[IESBMNT]

That works, thank you.

[rraggerr]

thanks!