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

Syntax

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

Parameters

pwszUserAgent [in]

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 locally.
WINHTTP_ACCESS_TYPE_DEFAULT_PROXY	Retrieves the static proxy or direct configuration from the registry. WINHTTP_ACCESS_TYPE_DEFAULT_PROXY does not inherit browser proxy settings. WinHTTP does not share any proxy settings with Internet Explorer. This option picks up the WinHTTP proxy configuration set by the WinHTTP Proxycfg.exe utility.
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 WINHTTP_ACCESS_TYPE_NAMED_PROXY.

 

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 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 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.

 

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.

Note  For Windows XP and Windows 2000, see Run-Time Requirements.

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

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Build date: 10/8/2009