.net - C# Asynchronous Pluggable Protocol wrapping default HTTP Protocol throws InvalidCastException -

in order able filter urls fetched (including js, images, etc.) c# web browser (winforms), containable option seems asynchronous pluggable protocol wrapping http (and later on others well). unfortunately fails invalidcastexception thrown original original protocol implementation after several calls <- weird part, seems succeed several times before failing.

now code:

firstly factory protocol registered , attached:

  var ep = new filteredhttpprotocolfactory();   guid id = guid.parse ("e00957bd-d0e1-4eb9-a025-7743fdc8b27b");   session.registernamespace (ep, ref id, "http", 0, null, 0); 

(the factory:)

[guid ("ef474615-8079-4cfa-b114-6d1d28634dd8")] [comvisible (true)] [classinterface (classinterfacetype.none)] public class filteredhttpprotocolfactory : iclassfactory {   public void createinstance (object punkouter, guid riid, out object ppvobject)   {     ppvobject = new filteredhttpprotocol();   }    public void lockserver (bool flock)   {   } } 

this original http protocol used ie, when using instead of wrapper works fine:

[comimport] [guid ("79eac9e2-baf9-11ce-8c82-00aa004ba90b")] public class originalhttphandler { } 

this wrapper itself:

[guid ("e00957bd-d0e1-4eb9-a025-7743fdc8b27b")] [comvisible (true)] [classinterface (classinterfacetype.none)] [asyncprotocol (name = "http2", description = "blah")] public class filteredhttpprotocol : iinternetprotocol, iinternetprotocolroot {  private readonly iinternetprotocol _wrapped;  public filteredhttpprotocol () {   var originalhttphandler = new originalhttphandler();   _wrapped = (iinternetprotocol) originalhttphandler; }  public void start (string szurl, iinternetprotocolsink sink, iinternetbindinfo poibindinfo, uint grfpi, uint dwreserved) {   _wrapped.start (szurl, sink, poibindinfo, grfpi, dwreserved); }  public void continue (ref _tagprotocoldata pprotocoldata) {   _wrapped.continue (ref pprotocoldata);      // <- fails here }    // .... other methods iinternetprotocol     public uint read (intptr pv, uint cb, out uint pcbread)     {       return _wrapped.read (pv, cb, out pcbread); // <- or here     } } 

so, weird part is, constructor called, start() called, read() , continue() called several times until whole thing fails (either read() or continue()) when parts of page visible (!), seems 1 specific image missing (mostly!) :

unable cast com object of type 'clients.windows.protocol.originalhttphandler'  interface type 'clients.windows.protocol.iinternetprotocol'. operation  failed because queryinterface call on com component interface  iid '{79eac9e4-baf9-11ce-8c82-00aa004ba90b}' failed due following  error: no such interface supported (exception hresult: 0x80004002 e_nointerface)). 

seeing cast object said interface several times (which should result in queryinterface() call every time, , has been called (verified through breakpoints , such) several times before fails error puzzling. looking @ ref counts ruled out object being disposed (wouldn't make sense anyway).

i have tried several things:

• google apps rare
• http://msdn.microsoft.com/en-us/library/aa767916(v=vs.85).aspx
• inheriting comimport'ed object - implementation gets ignored
• look @ ref counts
• casts of sorts
• check guids , interfaces mistakes
• asking colleagues

basically trying achieve wrap default http protocol implementation of ie filter out urls, including resources retrieved from. satisfied suitable alternatives, have compliant gplv2, deployable browser application, , no changes rest of system (i.e. no proxies).

thanks ;)

btw, going part of master's thesis here: http://desktopgap.codeplex.com

currently i'm investigating same behavior.

i have 2 ideas. first object called thread created:

method, apartment, threadid, objid -------------------- constructor: , sta, 9, #1 start: , sta, 9, #1 continue: , sta, 9, #1 read: , sta, 9, #1 read: , sta, 9, #1 lock: , sta, 9, #1 read: , sta, 9, #1 read: , sta, 9, #1 constructor: , sta, 10, #2 start: , sta, 10, #2 constructor: , sta, 10, #3   <-- notice threadid 10 terminate: , sta, 9, #1 start: , sta, 10, #3         <-- valid call constructor: , sta, 10, #4 start: , sta, 10, #4 read: , sta, 10, #4 continue: , mta, 11, #2 terminate: , sta, 10, #4 continue: , mta, 12, #3      <-- exception here!!! have new thread id of 12 , mta apartment constructor: , sta, 10, #5 start: , sta, 10, #5 constructor: , sta, 10, #6 unlock: , sta, 9, #1 start: , sta, 10, #6 

second thought clr handles com calls differently in native c++. i've faced when tried utilize directshow. in case of c++ takes pointer interface , invokes function via v-table. in case of managed code queries interface first. , additional query interface call fail or return wrong object if not implemented. solution create native iuknown wrapper return pointer iinternetprotocol on queryinterface.