WinHttpOpen function

The WinHttpOpen function initializes, for an application, the use of WinHTTP functions and returns a WinHTTP-session handle.

Syntax

HINTERNET WINAPI WinHttpOpen(
  _In_opt_ LPCWSTR pwszUserAgent,
  _In_     DWORD   dwAccessType,
  _In_     LPCWSTR pwszProxyName,
  _In_     LPCWSTR pwszProxyBypass,
  _In_     DWORD   dwFlags
);

Parameters

pwszUserAgent [in, optional]

A pointer to a string variable that contains the name of the application or entity calling the WinHTTP functions. This name is used as the user agent in the HTTP protocol.

dwAccessType [in]

Type of access required. This can be one of the following values.

Value	Meaning
WINHTTP_ACCESS_TYPE_NO_PROXY	Resolves all host names directly without a proxy.
WINHTTP_ACCESS_TYPE_DEFAULT_PROXY	Important  Use of this option is deprecated on Windows 8.1 and newer. Use WINHTTP_ACCESS_TYPE_AUTOMATIC_PROXY instead.   Retrieves the static proxy or direct configuration from the registry. WINHTTP_ACCESS_TYPE_DEFAULT_PROXY does not inherit browser proxy settings. The WinHTTP proxy configuration is set by one of these mechanisms. The proxycfg.exe utility on Windows XP and Windows Server 2003 or earlier. The netsh.exe utility on Windows Vista and Windows Server 2008 or later. WinHttpSetDefaultProxyConfiguration on all platforms.
WINHTTP_ACCESS_TYPE_NAMED_PROXY	Passes requests to the proxy unless a proxy bypass list is supplied and the name to be resolved bypasses the proxy. In this case, this function uses the values passed for pwszProxyName and pwszProxyBypass.
WINHTTP_ACCESS_TYPE_AUTOMATIC_PROXY	Uses system and per-user proxy settings (including the Internet Explorer proxy configuration) to determine which proxy/proxies to use. Automatically attempts to handle failover between multiple proxies, different proxy configurations per interface, and authentication. Supported in Windows 8.1 and newer.

 

pwszProxyName [in]

A pointer to a string variable that contains the name of the proxy server to use when proxy access is specified by setting dwAccessType to WINHTTP_ACCESS_TYPE_NAMED_PROXY. The WinHTTP functions recognize only CERN type proxies for HTTP. If dwAccessType is not set to WINHTTP_ACCESS_TYPE_NAMED_PROXY, this parameter must be set to WINHTTP_NO_PROXY_NAME.

pwszProxyBypass [in]

A pointer to a string variable that contains an optional semicolon delimited list of host names or IP addresses, or both, that should not be routed through the proxy when dwAccessType is set to WINHTTP_ACCESS_TYPE_NAMED_PROXY. The list can contain wildcard characters. Do not use an empty string, because the WinHttpOpen function uses it as the proxy bypass list. If this parameter specifies the "<local>" macro in the list as the only entry, this function bypasses any host name that does not contain a period. If dwAccessType is not set to WINHTTP_ACCESS_TYPE_NAMED_PROXY, this parameter must be set to WINHTTP_NO_PROXY_BYPASS.

dwFlags [in]

Unsigned long integer value that contains the flags that indicate various options affecting the behavior of this function. This parameter can have the following value.

Value	Meaning
WINHTTP_FLAG_ASYNC	Use the WinHTTP functions asynchronously. By default, all WinHTTP functions that use the returned HINTERNET handle are performed synchronously. When this flag is set, the caller needs to specify a callback function through WinHttpSetStatusCallback.

 

Return value

Returns a valid session handle if successful, or NULL otherwise. To retrieve extended error information, call GetLastError. Among the error codes returned are the following.

Remarks

Even when WinHTTP is used in asynchronous mode (that is, when WINHTTP_FLAG_ASYNC has been set in WinHttpOpen), this function operates synchronously. The return value indicates success or failure. To retrieve extended error information, call GetLastError.

The WinHttpOpen function is the first of the WinHTTP functions called by an application. It initializes internal WinHTTP data structures and prepares for future calls from the application. When the application finishes using the WinHTTP functions, it must call WinHttpCloseHandle to free the session handle and any associated resources.

The application can make any number of calls to WinHttpOpen, though a single call is normally sufficient. Each call to WinHttpOpen opens a new session context. Because user data is not shared between multiple session contexts, an application that makes requests on behalf of multiple users should create a separate session for each user, so as not to share user-specific cookies and authentication state. The application should define separate behaviors for each WinHttpOpen instance, such as different proxy servers configured for each.

After the calling application has finished using the HINTERNET handle returned by WinHttpOpen, it must be closed using the WinHttpCloseHandle function.

Examples

The following example code shows how to retrieve the default connection time-out value.

    DWORD data;
    DWORD dwSize = sizeof(DWORD);

    // Use WinHttpOpen to obtain an HINTERNET handle.
    HINTERNET hSession = WinHttpOpen(L"A WinHTTP Example Program/1.0", 
                                    WINHTTP_ACCESS_TYPE_DEFAULT_PROXY,
                                    WINHTTP_NO_PROXY_NAME, 
                                    WINHTTP_NO_PROXY_BYPASS, 0);
    if (hSession)
    {


        // Use WinHttpQueryOption to retrieve internet options.
        if (WinHttpQueryOption( hSession, 
                                WINHTTP_OPTION_CONNECT_TIMEOUT, 
                                &data, &dwSize))
        {
            printf("Connection timeout: %u ms\n\n",data);
        }
        else
        {
            printf( "Error %u in WinHttpQueryOption.\n", 
                    GetLastError());
        }        
        
        // When finished, release the HINTERNET handle.
        WinHttpCloseHandle(hSession);
    }
    else
    {
        printf("Error %u in WinHttpOpen.\n", GetLastError());
    }

Requirements

See also

About Microsoft Windows HTTP Services (WinHTTP)

WinHttpCloseHandle

WinHTTP Versions