IE BHO - DISPID_FILEDOWNLOAD being called for page loads? - c++

Question

I am implementing an Internet Explorer Browser Helper Object that should catch the DISPID_FILEDOWNLOAD event.
I first implemented this in C# which worked great except that I also need the cookies that go with the URL so need to call InternetGetCookiesEx. As .NET runs in it's own process it does not return me the session cookies so is no good.
I then wrote a quick test DLL in C++ so that it is loaded into the same process as IE which works great for the cookies but I now have a new problem:
I am getting calls to DISPID_FILEDOWNLOAD in my Invoke function for each page load when I only want them for an actual download.
In the C# version I only got a call to WebBrowser.FileDownload for an actual download but it seems that the C++ version is sending a DISPID_FILEDOWNLOAD even for each page load.
STDMETHODIMP CIEHlprObj::Invoke(
DISPID dispidMember,
REFIID riid,
LCID lcid,
WORD wFlags,
DISPPARAMS* pDispParams,
VARIANT* pvarResult,
EXCEPINFO* pExcepInfo,
UINT* puArgErr
)
{
USES_CONVERSION;
if (!pDispParams)
return E_INVALIDARG;
LPOLESTR lpURL = NULL;
m_spWebBrowser2->get_LocationURL(&lpURL);
int i = 0;
switch (dispidMember)
{
case DISPID_BEFORENAVIGATE2:
case DISPID_BEFORENAVIGATE:
sCurrentFile=NULL;
if (pDispParams->cArgs >= 5 && pDispParams->rgvarg[5].vt == (VT_BYREF | VT_VARIANT))
{
CComVariant varURL(*pDispParams->rgvarg[5].pvarVal);
varURL.ChangeType(VT_BSTR);
char* myStr = OLE2T(varURL.bstrVal);
if (myStr)
{
sCurrentFile = AllocateString(myStr);
sCurrentFileW = varURL.bstrVal;
}
}
break;
case DISPID_FILEDOWNLOAD:
// CALLED FOR EACH PAGE LOAD!
if(sCurrentFile)
{
TCHAR cookies[8192];
DWORD size = 8192;
BOOL ret = InternetGetCookieEx(sCurrentFile,
0,
cookies,
&size,
INTERNET_COOKIE_HTTPONLY,
0);
::MessageBox(0, sCurrentFile, "Downloading called multiple times!!", MB_OK);
}
break;
default:
break;
}
return S_OK;
}
Is there some filter that needs checking somewhere to know if a DISPID_FILEDOWNLOAD event relates to a file load or an actual file download?
Many thanks
UPDATE:
On closer inspection it seems that the C# managed code version is actually doing the same, I just didn't notice it the firs time around.
It seems that the FileDownload event is being called in the following circumstances:
New window / tab opened
New domain connected to (maybe a new keep-alive connection?)
An actual download
Obviously I only want the even on the actual download event.

Answer 1

As a possible solution to this I notice MS provide a ActiveDocument (BOOL) argument along with the event.. according to the Microsoft documentation the ActiveDocument argument means:
A Boolean that specifies whether the file is an Active Document
http://msdn.microsoft.com/en-us/library/bb268220(v=vs.85).aspx
Not very helpful but if I log the DISPID_FILEDOWNLOAD events to a text file and look at them later it appears that I should ignore all events where ActiveDocument = true
Getting the params is quite easy:
BOOL cancel = *pDispParams->rgvarg[0].pboolVal;
BOOL active = pDispParams->rgvarg[1].boolVal;
So the code would just need updating to something like:
if (active)
return S_OK;
I can only assume that this is some event the IE is sending telling the BHO that a page is downloading.. not a file, although that should mean that I get a DISPID_FILEDOWNLOAD event for each page load, which I don't.. only new tabs/browser instances and some new connections.
Hopefully someone else will be able to contribute to this and clarify what is the best way of handling this as it feels like a bit of a hack.