What initialization should be made prior to calling InternetGetProxyInfo()?

Question

I configured internet explorer to use a local PAC file:

It works just fine. But when I try to call InternetGetProxyInfo(), it fails with ERROR_CAN_NOT_COMPLETE. What can be the problem?

#ifndef WINVER              // Allow use of features specific to Windows XP or later.
#define WINVER 0x0501       // Change this to the appropriate value to target other versions of Windows.
#endif

#ifndef _WIN32_WINNT        // Allow use of features specific to Windows XP or later.                   
#define _WIN32_WINNT 0x0501 // Change this to the appropriate value to target other versions of Windows.
#endif                      

#include <winsock2.h>
#include <windows.h>
#include <wininet.h>
#include <tchar.h>

#define URL "http://www.yandex.ru/"
#define HOST "www.yandex.ru"

int _tmain(int argc, _TCHAR* argv[])
{
    char proxyBuffer[1024];
    char *str = proxyBuffer;
    DWORD nb = 1024;
    DWORD dw;
    BOOL b;
    pfnInternetGetProxyInfo pIGPI;                // Function-pointer instance

    /* code from MSDN: */    
    {
        HMODULE hModJS;                               // Handle for loading the DLL

        hModJS = LoadLibrary( TEXT("jsproxy.dll") );
        if (!hModJS)
        {
        _tprintf( TEXT("\nLoadLibrary failed to load jsproxy.dll with error: %d\n"),
        GetLastError( ) );
        return( FALSE );
        }

        pIGPI = (pfnInternetGetProxyInfo)
        GetProcAddress( hModJS, "InternetGetProxyInfo" );
        if (!pIGPI)         
        {
        _tprintf( TEXT("\nGetProcAddress failed to find InternetGetProxyInfo, error: %d\n"),
        GetLastError( ) );
        return( FALSE );
        }

        // The pIGPI function pointer can now be used to call InternetGetProxyInfo.
    }

    InternetInitializeAutoProxyDll(0); /* wininet.dll version of this function */
    SetLastError(0);
    b = pIGPI(URL,sizeof(URL),HOST,sizeof(HOST), &str, &nb);
    dw = GetLastError();

    SetLastError(0);
    b = pIGPI(URL,sizeof(URL)-1,HOST,sizeof(HOST)-1, &str, &nb);
    dw = GetLastError();

    return 0;
}

Please don't tell me to use other API, it's an educational, not practical question.

Answer 1

There are 2 ways:

• easy: call InternetOpenUrl() with a dummy URL to let wininet initialize jsproxy:

  #define URL "https://yandex.ru:777"
  #define HOST "yandex.ru"
  HINTERNET hInternet = InternetOpen(_T("try-wininet"), INTERNET_OPEN_TYPE_PRECONFIG, NULL, NULL, 0);
  HINTERNET hUrl = InternetOpenUrl(hInternet, _T("http://0.0.0.0"), NULL, 0, 0, 20);
  InternetCloseHandle(hUrl);
  InternetCloseHandle(hInternet);
  InternetGetProxyInfo(URL,sizeof(URL)-1,HOST,sizeof(HOST)-1, &str, &nb);
  GlobalFree(str);
  

• hard: call InternetInitializeAutoProxyDll() in jsproxy. But to prepare the arguments, you have to do everything yourself: read the settings from the registry, parse them, detect and download the PAC file and provide an implementation of AutoProxyHelperVtbl that contains such functions as GetIPAddress(), IsInNet(), etc.

InternetGetProxyInfo() fails when there's no PAC script configured, although some proxy server is set in the bottom of the dialog. In this case you should call InternetQueryOption(NULL, INTERNET_OPTION_PROXY,...)