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/advanced/server-flex/advanced_server_flex.cpp

@@ -251,6 +251,16 @@ public:
             websocket::stream_base::suggested_settings(
                 websocket::role_type::server));
 
+        // Set a decorator to change the Server of the handshake
+        derived().ws().set_option(
+            websocket::stream_base::decorator(
+            [](websocket::response_type& res)
+            {
+                res.set(http::field::server,
+                    std::string(BOOST_BEAST_VERSION_STRING) +
+                        " advanced-server-flex");
+            }));
+
         // Accept the websocket handshake
         derived().ws().async_accept(
             req,

example/advanced/server/advanced_server.cpp

@@ -229,10 +229,6 @@ public:
     websocket_session(tcp::socket socket)
         : ws_(std::move(socket))
     {
-        // Set suggested timeout settings for the websocket
-        ws_.set_option(
-            websocket::stream_base::suggested_settings(
-                websocket::role_type::server));
     }
 
     // Start the asynchronous accept operation
@@ -240,6 +236,20 @@ public:
     void
     do_accept(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) +
+                        " advanced-server");
+            }));
+
         // Accept the websocket handshake
         ws_.async_accept(
             req,