Make permessage-deflate status queryable in websocket::stream

include/boost/beast/websocket/detail/impl_base.hpp

@@ -345,6 +345,12 @@ struct impl_base<true>
             result = clamp(result, rd_msg_max);
         return result;
     }
+
+    void
+    get_config_pmd(detail::pmd_offer &pmd)
+    {
+        pmd = pmd_config_;
+    }
 };
 
 //------------------------------------------------------------------------------
@@ -495,6 +501,12 @@ struct impl_base<false>
             result = clamp(result, rd_msg_max);
         return result;
     }
+
+    void
+    get_config_pmd(detail::pmd_offer &pmd)
+    {
+        pmd = {};
+    }
 };
 
 } // detail

include/boost/beast/websocket/impl/stream.hpp

@@ -175,6 +175,18 @@ get_option(timeout& opt)
     opt = impl_->timeout_opt;
 }
 
+template <class NextLayer, bool deflateSupported>
+void
+stream<NextLayer, deflateSupported>::
+get_status(permessage_deflate_status &status) const noexcept
+{
+    detail::pmd_offer pmd;
+    impl_->get_config_pmd(pmd);
+    status.active               = pmd.accept;
+    status.client_window_bits   = pmd.client_max_window_bits;
+    status.server_window_bits   = pmd.server_max_window_bits;
+}
+
 template<class NextLayer, bool deflateSupported>
 void
 stream<NextLayer, deflateSupported>::

include/boost/beast/websocket/stream.hpp

@@ -38,6 +38,25 @@
 namespace boost {
 namespace beast {
 namespace websocket {
+/** permessage-deflate extension status.
+
+    These settings indicate the status of the permessage-deflate
+    extension, showing if it is active and the window bits in use.
+
+    Objects of this type are used with
+    @ref beast::websocket::stream::get_status.
+*/
+struct permessage_deflate_status
+{
+    /// `true` if the permessage-deflate extension is active
+    bool active = false;
+
+    /// The number of window bits used by the client
+    int client_window_bits = 0;
+
+    /// The number of window bits used by the server
+    int server_window_bits = 0;
+};
 
 /** The type of received control frame.
 
@@ -411,6 +430,24 @@ class stream
     void
     get_option(permessage_deflate& o);
 
+    /** Get the status of the permessage-deflate extension.
+
+        Used to check the status of the permessage-deflate extension after
+        the WebSocket handshake.
+
+        @param status A reference to a `permessage_deflate_status` object
+        where the status will be stored.
+
+        @par Example
+        Checking the status of the permessage-deflate extension:
+        @code
+            permessage_deflate_status status;
+            ws.get_status(status);
+        @endcode
+    */
+    void
+    get_status(permessage_deflate_status &status) const noexcept;
+
     /** Set the automatic fragmentation option.
 
         Determines if outgoing message payloads are broken up into

test/beast/websocket/handshake.cpp

@@ -136,6 +136,61 @@ class handshake_test : public websocket_test_suite
             }
             ts.close();
         });
+
+        // handshake, deflate, supported
+        doStreamLoop([&](test::stream &ts)
+        {
+            echo_server es{log};
+            ws_type ws{ts};
+            ws.next_layer().connect(es.stream());
+            response_type res;
+            try
+            {
+                websocket::permessage_deflate option{};
+                option.client_enable = true;
+                option.client_max_window_bits = 14;
+                ws.set_option(option);
+
+                w.handshake(ws, res, "localhost", "/");
+
+                websocket::permessage_deflate_status status;
+                ws.get_status(status);
+                BEAST_EXPECT(status.active);
+                BEAST_EXPECT(9 == status.server_window_bits);
+                BEAST_EXPECT(14 == status.client_window_bits);
+            }
+            catch(...)
+            {
+                ts.close();
+                throw;
+            }
+            ts.close(); 
+        });
+
+        // handshake, deflate, not supported
+        doStreamLoop([&](test::stream &ts)
+        {
+            echo_server es{log};
+            ws_type_t<false> ws{ts};
+            ws.next_layer().connect(es.stream());
+            response_type res;
+            try
+            {
+                w.handshake(ws, res, "localhost", "/");
+
+                websocket::permessage_deflate_status status;
+                ws.get_status(status);
+                BEAST_EXPECT(!status.active);
+                BEAST_EXPECT(0 == status.server_window_bits);
+                BEAST_EXPECT(0 == status.client_window_bits);
+            }
+            catch(...)
+            {
+                ts.close();
+                throw;
+            }
+            ts.close();
+        });
     }
 
     void