The WinHttpOpen function initializes, for an application, the use of WinHTTP functions and returns a WinHTTP-session handle.
WINHTTPAPI HINTERNET WinHttpOpen( LPCWSTR pszAgentW, DWORD dwAccessType, LPCWSTR pszProxyW, LPCWSTR pszProxyBypassW, DWORD dwFlags );
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.
Type of access required. This can be one of the following values.
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.
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.
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.
||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.|
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.
||An internal error has occurred.|
||Not enough memory was available to complete the requested operation. (Windows error code)|
We strongly recommend that you use WinHTTP in asynchronous mode (that is, when WINHTTP_FLAG_ASYNC has been set in WinHttpOpen, so that usage of the returned HINTERNET become asynchronous). 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.
The following example code shows how to retrieve the default connection time-out value.
DWORD data; DWORD dwSize = sizeof(DWORD);
|Minimum supported client||Windows XP, Windows 2000 Professional with SP3 [desktop apps only]|
|Minimum supported server||Windows Server 2003, Windows 2000 Server with SP3 [desktop apps only]|
|Redistributable||WinHTTP 5.0 and Internet Explorer 5.01 or later on Windows XP and Windows 2000.|