Add websocket-chat-multi example:

This is the multi-threaded io_context version of the
CppCon2018 WebSocket chat server and client example.

example/websocket/server/chat-multi/websocket_session.hpp

@@ -0,0 +1,70 @@
+//
+// Copyright (c) 2018 Vinnie Falco (vinnie dot falco at gmail dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+// Official repository: https://github.com/vinniefalco/CppCon2018
+//
+
+#ifndef BOOST_BEAST_EXAMPLE_WEBSOCKET_CHAT_MULTI_WEBSOCKET_SESSION_HPP
+#define BOOST_BEAST_EXAMPLE_WEBSOCKET_CHAT_MULTI_WEBSOCKET_SESSION_HPP
+
+#include "net.hpp"
+#include "beast.hpp"
+#include "shared_state.hpp"
+
+#include <cstdlib>
+#include <memory>
+#include <string>
+#include <vector>
+
+// Forward declaration
+class shared_state;
+
+/** Represents an active WebSocket connection to the server
+*/
+class websocket_session : public boost::enable_shared_from_this<websocket_session>
+{
+    beast::flat_buffer buffer_;
+    websocket::stream<tcp::socket> ws_;
+    boost::shared_ptr<shared_state> state_;
+    std::vector<boost::shared_ptr<std::string const>> queue_;
+    net::strand<net::io_context::executor_type> strand_;
+
+    void fail(beast::error_code ec, char const* what);
+    void on_accept(beast::error_code ec);
+    void on_read(beast::error_code ec, std::size_t bytes_transferred);
+    void on_write(beast::error_code ec, std::size_t bytes_transferred);
+
+public:
+    websocket_session(
+        tcp::socket socket,
+        boost::shared_ptr<shared_state> const& state);
+
+    ~websocket_session();
+
+    template<class Body, class Allocator>
+    void
+    run(http::request<Body, http::basic_fields<Allocator>> req);
+
+    // Send a message
+    void
+    send(boost::shared_ptr<std::string const> const& ss);
+};
+
+template<class Body, class Allocator>
+void
+websocket_session::
+run(http::request<Body, http::basic_fields<Allocator>> req)
+{
+    // Accept the websocket handshake
+    ws_.async_accept(
+        req,
+        std::bind(
+            &websocket_session::on_accept,
+            shared_from_this(),
+            std::placeholders::_1));
+}
+
+#endif