Better WebSocket decorator:

* Caller provided type can omit one or both overloads
* Omitted overloads yield default behavior
* Documentation no longer refers to a detail type

CHANGELOG.md

@@ -3,6 +3,7 @@
 * Add missing rebind to handler_alloc
 * Fix error handling in http server examples
 * Fix CMake scripts for MinGW
+* Better WebSocket decorator
 
 --------------------------------------------------------------------------------
 

include/beast/websocket/detail/decorator.hpp

@@ -11,6 +11,7 @@
 #include <beast/http/empty_body.hpp>
 #include <beast/http/message.hpp>
 #include <beast/http/string_body.hpp>
+#include <beast/version.hpp>
 #include <utility>
 
 namespace beast {
@@ -40,6 +41,32 @@ class decorator : public abstract_decorator
 {
     T t_;
 
+    class call_req_possible
+    {
+        template<class U, class R = decltype(
+            std::declval<U>().operator()(
+                std::declval<request_type&>()),
+                    std::true_type{})>
+        static R check(int);
+        template<class>
+        static std::false_type check(...);
+    public:
+        using type = decltype(check<T>(0));
+    };
+
+    class call_res_possible
+    {
+        template<class U, class R = decltype(
+            std::declval<U>().operator()(
+                std::declval<response_type&>()),
+                    std::true_type{})>
+        static R check(int);
+        template<class>
+        static std::false_type check(...);
+    public:
+        using type = decltype(check<T>(0));
+    };
+
 public:
     decorator() = default;
 
@@ -56,38 +83,45 @@ public:
     void
     operator()(request_type& req) override
     {
-        t_(req);
+        (*this)(req, typename call_req_possible::type{});
     }
 
     void
     operator()(response_type& resp) override
     {
-        t_(resp);
+        (*this)(resp, typename call_res_possible::type{});
+    }
+
+private:
+    void
+    operator()(request_type& req, std::true_type)
+    {
+        t_(req);
+    }
+
+    void
+    operator()(request_type& req, std::false_type)
+    {
+        req.headers.replace("User-Agent",
+            std::string{"Beast/"} + BEAST_VERSION_STRING);
+    }
+
+    void
+    operator()(response_type& res, std::true_type)
+    {
+        t_(res);
+    }
+
+    void
+    operator()(response_type& res, std::false_type)
+    {
+        res.headers.replace("Server",
+            std::string{"Beast/"} + BEAST_VERSION_STRING);
     }
 };
 
 struct default_decorator
 {
-    static
-    char const*
-    version()
-    {
-        return "Beast.WSProto/1.0";
-    }
-
-    template<class Body, class Headers>
-    void
-    operator()(http::message<true, Body, Headers>& req)
-    {
-        req.headers.replace("User-Agent", version());
-    }
-
-    template<class Body, class Headers>
-    void
-    operator()(http::message<false, Body, Headers>& resp)
-    {
-        resp.headers.replace("Server", version());
-    }
 };
 
 using decorator_type =

include/beast/websocket/stream.hpp

@@ -177,9 +177,29 @@ public:
             wr_frag_size_ = o.value;
     }
 
-    /// Set the decorator used for HTTP messages
+    /** Set the decorator used for HTTP messages.
+
+        The value for this option is a callable type with two
+        optional signatures:
+
+        @code
+            void(request_type&);
+
+            void(response_type&);
+        @endcode
+
+        If a matching signature is provided, the callable type
+        will be invoked with the HTTP request or HTTP response
+        object as appropriate. When a signature is omitted,
+        a default consisting of the string Beast followed by
+        the version number is used.
+    */
     void
+#if GENERATING_DOCS
+    set_option(implementation_defined o)
+#else
     set_option(detail::decorator_type o)
+#endif
     {
         d_ = std::move(o);
     }