webui: introduce hook to modify web page delivered by WS handler

This could be used to insert specialized information, which is related
to WS handler or display engine like CEF/Qt5

gui/cefdisplay/src/simple_app.cxx

@@ -58,6 +58,11 @@ protected:
 
    CefRefPtr<CefCallback> fCallBack{nullptr};
 
+   void CheckWSPageContent(THttpWSHandler *) override
+   {
+
+   }
+
 public:
    explicit TCefHttpCallArg() = default;
 

gui/qt5webdisplay/rooturlschemehandler.cpp

@@ -62,6 +62,10 @@ class TWebGuiCallArg : public THttpCallArg {
 protected:
    UrlRequestJobHolder fRequest;
 
+   void CheckWSPageContent(THttpWSHandler *) override
+   {
+   }
+
 public:
    explicit TWebGuiCallArg(QWebEngineUrlRequestJob *req = nullptr) : THttpCallArg(), fRequest(req) {}
 

net/http/inc/THttpCallArg.h

@@ -25,6 +25,7 @@ class THttpWSEngine;
 class THttpWSHandler;
 
 class THttpCallArg : public TObject {
+
    friend class THttpServer;
    friend class THttpWSEngine;
    friend class THttpWSHandler;
@@ -63,7 +64,7 @@ protected:
 private:
    std::shared_ptr<THttpWSEngine> fWSEngine; ///<!  web-socket engine, which supplied to run created web socket
 
-   std::string  fContent;  ///!< content - text or binary
+   std::string  fContent;  ///<! content - text or binary
    std::string  fPostData; ///<! data received with post request - text - or binary
 
    void AssignWSId();
@@ -71,6 +72,9 @@ private:
 
    void ReplaceAllinContent(const std::string &from, const std::string &to);
 
+   /** Method used to modify content of web page used by web socket handler */
+   virtual void CheckWSPageContent(THttpWSHandler *) {}
+
 public:
    explicit THttpCallArg() = default;
    virtual ~THttpCallArg();

net/http/src/THttpServer.cxx

@@ -751,6 +751,8 @@ void THttpServer::ProcessRequest(THttpCallArg *arg)
                arg->fContent = ReadFileContent(resolve.Data());
                arg->AddNoCacheHeader();
             }
+
+            arg->CheckWSPageContent(handler);
          }
       }