[webkit-gtk] Calling a native (compiled) subprogram from JavaScript in WebKitGTK

[Leo Ufimtsev]

Hello Ludovic,

I'm doing something similar right now.

For webkit2:
- you need to compile a webextension
- The web extension deals with interacting with javascript
- You'd have to use gdbus to communicate with main process.

I have a few snippets that implement the above:
- Basic webextension:
https://github.com/LeoUfimtsev/LeoGtk3/tree/master/snip_Webkit_ExtensionMinimum
- Basic webextension, where javascript calls are handled by c:
https://github.com/LeoUfimtsev/LeoGtk3/tree/master/snip_Webkit_ExtensionJavascriptCoreFunc
- Basic GDbus snippet:
https://github.com/LeoUfimtsev/LeoGtk3/tree/master/snip_GDBus
- Basic webkextension, where javascript calls C and C reached main process
over GDBus:
https://github.com/LeoUfimtsev/LeoGtk3/tree/master/snip_Webkit_Ext_JSC_GDBus

It's a lot of work, but currently afaik the only way of doing it.

Let me know if you have any questions about the above.



On Tue, Sep 12, 2017 at 10:29 AM, Ludovic Brenta <ludovic at ludovic-brenta.org
> wrote:

> Hello,
>
> I am extending a multi-million-line-of-code application written
> in Ada with a new WebKitGTK browser window, using the WebKit2GTK
> API.
>
> After reading [1]  and [2] I am trying to expose an Ada (or C,
> C++, Vala, whatever) subprogram to the JavaScript engine in
> WebKit, so that JavaScript code can call it.
>
> [1] http://www.davedoesdev.com/wrapping-webkit-part-1-gtk+-vala/
> [2] https://karhm.com/JavaScriptCore_C_API/
>
> The gist of it is: attach a callback to the "load-changed" signal
> of the WebKitWebView. If the Load_Event is "finished", create a
> new function object (by calling JSObjectMakeFunctionWithCallback);
> add to the global object of the WebView a new property whose name
> is the name of the function as seen from JavaScript and the value
> is the function object.
>
> If I try to call the function thus exported (and aptly named
> "exported"), the JavaScript engine throws:
>
>  ReferenceError: Can't find variable: exported
>
> I am suspecting that I'm attaching the property to the wrong
> global object.  Since I'm stuck with Red Hat Enterprise Linux
> and the webkitgtk3-devel-2.4.9-6.el7.x86_64 package, I have no
> debugging info available for WebKit itself (only for the host
> application), so I can't easily debug what's happening.  All I
> can tell for sure is that Get_Javascript_Global_Context,
> Get_Global_Object, String.To_JavaScript etc all return non-null
> and that Exceptions remain null after the call to Set_Property.
> Am I doing something wrong?  Is this feature even supported with
> WebKit2 or should I switch to the deprecated WebKit 1 that does not
> use a separate process?
>
>   type Attribute_T is (None, Read_Only, Dont_Enum, Dont_Delete);
>   type Attributes_T is array (Attribute_T) of Boolean with Pack, Size =>
> Interfaces.C.unsigned'Size;
>
>   function Get_Global_Object (Ctx : in Context_T) return T
>     with Convention => C, Import, External_Name =>
> "JSContextGetGlobalObject";
>
>   procedure Set_Property (Ctx           : in     Context_T;
>                           Object        : in     T;
>                           Property_Name : in     String.T;
>                           New_Value     : in     Value.T;
>                           Attributes    : in     Attributes_T;
>                           Exceptions    :    out Value.T)
>     with Convention => C, Import, External_Name => "JSObjectSetProperty";
>
>   type Callback_T is access function (Ctx            : in     Context_T;
>                                       Func           : in     T;
>                                       This           : in     T;
>                                       Argument_Count : in
>  Interfaces.C.size_t;
>                                       Arguments      : in
>  Value.Arrays.Pointer;
>                                       Exceptions     :    out Value.T)
> return Value.T with Convention => C;
>
>   function Make_Function_With_Callback (Ctx : in Context_T; Name : in
> String.T; Callback : in Callback_T) return T
>     with Convention => C, Import, External_Name =>
> "JSObjectMakeFunctionWithCallback";
>
>   procedure Export_Ada_Function_To_Javascript (Ctx             : in
> Context_T;
>                                                Javascript_Name : in
> Standard.String;
>                                                Ada_Function    : in
> Callback_T) is
>     Global : constant T := Get_Global_Object (Ctx);
>     Name : constant String.T := String.To_Javascript (Javascript_Name);
>     Func_Obj : constant T := Make_Function_With_Callback (Ctx,
>                                                           Name => Name,
>                                                           Callback =>
> Ada_Function);
>     Exceptions : Value.T;
>   begin
>     Set_Property (Ctx,
>                   Object        => Global,
>                   Property_Name => Name,
>                   New_Value     => Value.T (Func_Obj),
>                   Attributes    => (Read_Only => True, others => False),
>                   Exceptions    => Exceptions);
>     -- TODO: log Exceptions, possibly raise an Ada exception?
>   end Export_Ada_Function_To_Javascript;
>
>     procedure On_Load_Changed (View       : not null access
> Webkit.Web_View.Record_T'Class;
>                                Load_Event : in
> Webkit.Web_View.Load_Event_T) is
>     begin
>       case Load_Event is
>         when Webkit.Web_View.Started | Webkit.Web_View.Redirected |
> Webkit.Web_View.Committed => null;
>         when Webkit.Web_View.Finished =>
>           Javascript.Object.Export_Ada_Function_To_Javascript (Ctx =>
> View.Get_Javascript_Global_Context,
>
>  Javascript_Name => "exported",
>
>  Ada_Function => Exported'Access);
>       end case;
>     exception
>       when others =>
>         UIF_Error.Report (Kind      => UIF_Error.Operation_Aborted,
>                           Unit_Name => Display_Name,
>                           Message   => "Exception in
> Regulation_Editor.Browser_Window.On_Load_Changed");
>     end On_Load_Changed;
>
> --
> Ludovic Brenta.
>
> _______________________________________________
> webkit-gtk mailing list
> webkit-gtk at lists.webkit.org
> https://lists.webkit.org/mailman/listinfo/webkit-gtk
>



-- 
Leo Ufimtsev, Software Engineer, Red Hat
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