Question

I have the following code:

void SendRequest(HINTERNET connection, LPCWSTR method, LPCWSTR referer,LPCWSTR path,WINHTTP_STATUS_CALLBACK whCallback){    
    HINTERNET request;
    request=WinHttpOpenRequest( connection, 0,path,0,referer,WINHTTP_DEFAULT_ACCEPT_TYPES,0);
    WinHttpSetStatusCallback(request, (WINHTTP_STATUS_CALLBACK)whCallback,WINHTTP_CALLBACK_FLAG_ALL_NOTIFICATIONS,0);
    REQUEST_CONTEXT cpContext;
    WinHttpSendRequest(request,WINHTTP_NO_ADDITIONAL_HEADERS,0,NULL,NULL,NULL,(DWORD_PTR)&cpContext);
};

WinHttpSendRequest does not block, so once it is executed, the function ends. However, WinHttpSendRequest callback to another function with the cpContext as a parameter. So my question is, doe cpContext gets destroyed after the function ends? Does this result in a a memory leak since there is no way to access cpContext outside the function? How can I do this in best C++ practice?

Answer 1

cpContext is destroyed at the end of the function. This results in undefined behavior because cpContext may be destroyed before the callback is invoked. If you dereference the pointer to it from within the callback, this is undefined behavior. One way to solve this would be to avoid using a locally-scoped variable:

REQUEST_CONTEXT* cpContext = new REQUEST_CONTEXT();
WinHttpSendRequest(request,WINHTTP_NO_ADDITIONAL_HEADERS,0,NULL,NULL,NULL,(DWORD_PTR)cpContext);

Don’t forget to delete it within the callback function.

The leak would be the HINTERNET handle, unless you are closing it in your callback. This handle needs to be closed with WinHttpCloseHandle, but you cannot close it while the asynchronous request is active.