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/http_session.hpp

@@ -0,0 +1,57 @@
+//
+// 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_HTTP_SESSION_HPP
+#define BOOST_BEAST_EXAMPLE_WEBSOCKET_CHAT_MULTI_HTTP_SESSION_HPP
+
+#include "net.hpp"
+#include "beast.hpp"
+#include "shared_state.hpp"
+#include <boost/smart_ptr.hpp>
+#include <cstdlib>
+#include <memory>
+
+/** Represents an established HTTP connection
+*/
+class http_session : public boost::enable_shared_from_this<http_session>
+{
+    tcp::socket socket_;
+    beast::flat_buffer buffer_;
+    boost::shared_ptr<shared_state> state_;
+    http::request<http::string_body> req_;
+    net::strand<net::io_context::executor_type> strand_;
+
+    struct send_lambda
+    {
+        http_session& self_;
+
+        explicit
+        send_lambda(http_session& self)
+            : self_(self)
+        {
+        }
+
+        template<bool isRequest, class Body, class Fields>
+        void
+        operator()(http::message<isRequest, Body, Fields>&& msg) const;
+    };
+
+    void fail(beast::error_code ec, char const* what);
+    void on_read(beast::error_code ec, std::size_t);
+    void on_write(beast::error_code ec, std::size_t, bool close);
+
+public:
+    http_session(
+        tcp::socket socket,
+        boost::shared_ptr<shared_state> const& state);
+
+    void run();
+};
+
+#endif