How To Get Protocol Headers in a Pluggable Protocol Handler (279497)

MORE INFORMATION

• A URL moniker client can optionally implement the IHttpNegotiate interface. This interface has a BeginningTransaction method that the protocol handler can call at the beginning of a URL navigation. This method allows the client to add headers, such as Accept-Language, or User-Agent, to the request.
  
  A specific example is MSHTML as an URL moniker host. MSHTML asks the WebBrowser, and the WebBrowser in turn asks its host, for a new user agent by way of the DISPID_AMBIENT_USERAGENT property when navigating to clicked hyperlinks. For additional information, click the article number below to view the article in the Microsoft Knowledge Base:

  183412 PRB: WebBrowser Control Clients Share Global Settings

  MSHTML returns this user agent string when its implementation of IHttpNegotiate::BeginningTransaction is called. The advantage of this method is that headers can be fine-tuned on a per-instance basis (as opposed to a process-global basis).
• A client can use the ::UrlMkSetSessionOption function to communicate headers to the APPH. This function sets options on a process-global basis.

1. QueryService the IInternetProtocolSink obtained from IInternetProtocol::Start for IHttpNegotiate. Then call the BeginningTransaction method to get the headers.
   
   For instance, within IInternetProtocol::Start

   	IHttpNegotiate *pHttpNeg;
   	hr = IUnknown_QueryService(pIProtSink, IID_IHttpNegotiate, IID_IHttpNegotiate, (void**)&pHttpNeg);
   
   	if(SUCCEEDED(hr))
   	{
   		LPWSTR pwzAddHeaders = NULL;
   		hr = pHttpNeg->BeginningTransaction(szUrl, NULL, NULL, &pwzAddHeaders);
   
   		// pwzAddHeaders now contains headers.
   		// The headers have the same form as they
   		// would in an HTTP request. That is,
   		// of the form: 
   		// "Header-Name: Header-Value\r\n2nd-Header-Name: 2nd-Header-Value\r\n"
   		// and so on.
   		.
   		.
   		.
   		pHttpNeg->Release();
   	}
   						

   Where the IUnknown_QueryService() function resembles the following:

   
   HRESULT IUnknown_QueryService(IUnknown* punk, REFGUID rsid, REFIID riid, void ** ppvObj)
   {
       HRESULT hr = E_NOINTERFACE;
   
       *ppvObj = 0;
   
       if (punk)
       {
           IServiceProvider *pSrvPrv;
           hr = punk->QueryInterface(IID_IServiceProvider, (void **) &pSrvPrv);
           if (hr == NOERROR)
           {
               hr = pSrvPrv->QueryService(rsid,riid, ppvObj);
               pSrvPrv->Release();
           }
       }
   
       return hr;
   }
   
   					

2. Retrieve per-process settings for values that you didn't obtain from the above method, by using ::UrlMkGetSessionOption(). For instance, to retrieve the "User-Agent" header:

   	char cUAStr[_MAX_PATH];
   	DWORD nUAStrLen = sizeof(cUAStr)/sizeof(cUAStr[0]) - 1;
   	::UrlMkGetSessionOption(URLMON_OPTION_USERAGENT, cUAStr, nUAStrLen, &nUAStrLen, 0);
   
   	// Alternatively, for "User-Agent", this API can be used:
   	// ::ObtainUserAgentString (0, cUAStr, &nUAStrLen);