WebSocket Decorator is a socket option (API Change):

This changes the interface used to apply a decorator to the HTTP
request or response messages used to perform the WebSocket handshake
as follows:

* Add the `stream_base::decorator` option object

* Add `stream::set_option` overload to set the decorator from
  the option

* The decorator applies to all client and server handshakes
  performed on the stream after the option is set.

* Overloads of the following functions which accept a Decorator
  are deprecated:
  - accept, accept_ex
  - handshake, handshake_ex
  - async_accept, async_accept_ex
  - async_handshake, async_handshake_ex

Actions Required:

* Code which passes decorator to any `websocket::stream` member
  function should call `stream::set_option` instead with a newly
  constructed `stream_base::decorator` object containing the
  decorator. Alternatively, the macro `BOOST_BEAST_ALLOW_DEPRECATED`
  may be defined to 1.

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

@@ -17,10 +17,6 @@ websocket_session(
     : ws_(std::move(socket))
     , state_(state)
 {
-    // Set suggested timeout settings for the websocket
-    ws_.set_option(
-        websocket::stream_base::suggested_settings(
-            websocket::role_type::server));
 }
 
 websocket_session::

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

@@ -57,6 +57,20 @@ void
 websocket_session::
 run(http::request<Body, http::basic_fields<Allocator>> req)
 {
+    // Set suggested timeout settings for the websocket
+    ws_.set_option(
+        websocket::stream_base::suggested_settings(
+            websocket::role_type::server));
+
+    // Set a decorator to change the Server of the handshake
+    ws_.set_option(websocket::stream_base::decorator(
+        [](websocket::response_type& res)
+        {
+            res.set(http::field::server,
+                std::string(BOOST_BEAST_VERSION_STRING) +
+                    " websocket-chat-multi");
+        }));
+
     // Accept the websocket handshake
     ws_.async_accept(
         req,