API FlagsAPI Flags*
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API Flags

Many of the Win32 Internet functions accept a double-word array of flags as a parameter. The following is a brief description of the defined flags.

INTERNET_FLAG_ASYNC
Makes only asynchronous requests on handles descended from the handle returned from this function. Only the InternetOpen function uses this flag.
INTERNET_FLAG_CACHE_ASYNC
Allows a lazy cache write.
INTERNET_FLAG_CACHE_IF_NET_FAIL
Return the resource from the cache if the network request for the resource fails due to an ERROR_INTERNET_CONNECTION_RESET or ERROR_INTERNET_CANNOT_CONNECT. This flag is used by HttpOpenRequest.
INTERNET_FLAG_DONT_CACHE
Does not add the returned entity to the cache. Identical to the preferred value, INTERNET_FLAG_NO_CACHE_WRITE. This flag is used by GopherFindFirstFile, GopherOpenFile, FtpFindFirstFile, FtpGetFile, FtpOpenFile, FtpPutFile, HttpOpenRequest, and InternetOpenUrl.
INTERNET_FLAG_EXISTING_CONNECT
Attempts to use an existing InternetConnect object if one exists with the same attributes required to make the request. This is useful only with FTP operations, since FTP is the only protocol that typically performs multiple operations during the same session. The Win32 Internet API caches a single connection handle for each HINTERNET handle generated by InternetOpen. Only the InternetOpenUrl function uses this flag.
INTERNET_FLAG_FORMS_SUBMIT
Indicates that this is a forms submit.
INTERNET_FLAG_FROM_CACHE
Does not make network requests. All entities are returned from the cache. If the requested item is not in the cache, a suitable error, such as ERROR_FILE_NOT_FOUND, is returned. Only the InternetOpen function uses this flag.
INTERNET_FLAG_HYPERLINK
Forces a reload if there was no Expires time and no Last-Modified time returned from the server when determining whether to reload the item from the network. This flag can be used by GopherFindFirstFile, GopherOpenFile, FtpFindFirstFile, FtpGetFile, FtpOpenFile, FtpPutFile, HttpOpenRequest, and InternetOpenUrl.
INTERNET_FLAG_IGNORE_CERT_CN_INVALID
Disables Win32 Internet function checking of SSL/PCT-based certificates that are returned from the server against the host name given in the request. Win32 Internet functions use a simple check against certificates by comparing for matching host names and simple wildcarding rules. This flag can be used by HttpOpenRequest and InternetOpenUrl (for HTTP requests).
INTERNET_FLAG_IGNORE_CERT_DATE_INVALID
Disables Win32 Internet function checking of SSL/PCT-based certificates for proper validity dates. This flag can be used by HttpOpenRequest and InternetOpenUrl (for HTTP requests).
INTERNET_FLAG_IGNORE_REDIRECT_TO_HTTP
Disables the ability of the Win32 Internet functions to detect this special type of redirect. When this flag is used, Win32 Internet functions transparently allow redirects from HTTPS to HTTP URLs. This flag can be used by HttpOpenRequest and InternetOpenUrl (for HTTP requests).
INTERNET_FLAG_IGNORE_REDIRECT_TO_HTTPS
Disables the ability of the Win32 Internet functions to detect this special type of redirect. When this flag is used, Win32 Internet functions transparently allow redirects from HTTP to HTTPS URLs. This flag can be used by HttpOpenRequest and InternetOpenUrl (for HTTP requests).
INTERNET_FLAG_KEEP_CONNECTION
Uses keep-alive semantics, if available, for the connection. This flag is used by HttpOpenRequest and InternetOpenUrl (for HTTP requests). This flag is required for Microsoft Network (MSN), NT LAN Manager (NTLM), and other types of authentication.
INTERNET_FLAG_MAKE_PERSISTENT
No longer supported.
INTERNET_FLAG_MUST_CACHE_REQUEST
Identical to the preferred value, INTERNET_FLAG_NEED_FILE. Causes a temporary file to be created if the file cannot be cached. This flag can be used by GopherFindFirstFile, GopherOpenFile, FtpFindFirstFile, FtpGetFile, FtpOpenFile, FtpPutFile, HttpOpenRequest, and InternetOpenUrl.
INTERNET_FLAG_NEED_FILE
Causes a temporary file to be created if the file cannot be cached. This flag can be used by GopherFindFirstFile, GopherOpenFile, FtpFindFirstFile, FtpGetFile, FtpOpenFile, FtpPutFile, HttpOpenRequest, and InternetOpenUrl.
INTERNET_FLAG_NO_AUTH
Does not attempt authentication automatically. This flag can be used by HttpOpenRequest and InternetOpenUrl (for HTTP requests).
INTERNET_FLAG_NO_AUTO_REDIRECT
Does not automatically handle redirection in HttpSendRequest. This flag can also be used by InternetOpenUrl for HTTP requests.
INTERNET_FLAG_NO_CACHE_WRITE
Does not add the returned entity to the cache. This flag is used by GopherFindFirstFile, GopherOpenFile, FtpFindFirstFile, FtpGetFile, FtpOpenFile, FtpPutFile, HttpOpenRequest, and InternetOpenUrl.
INTERNET_FLAG_NO_COOKIES
Does not automatically add cookie headers to requests, and does not automatically add returned cookies to the cookie database. This flag can be used by HttpOpenRequest and InternetOpenUrl (for HTTP requests).
INTERNET_FLAG_NO_UI
Disables the cookie dialog box. This flag can be used by HttpOpenRequest and InternetOpenUrl (HTTP requests only).
INTERNET_FLAG_OFFLINE
Identical to INTERNET_FLAG_FROM_CACHE. Does not make network requests. All entities are returned from the cache. If the requested item is not in the cache, a suitable error, such as ERROR_FILE_NOT_FOUND, is returned. Only the InternetOpen function uses this flag.
INTERNET_FLAG_PASSIVE
Uses passive FTP semantics. Only InternetConnect and InternetOpenUrl use this flag. InternetConnect uses this flag for FTP requests, and InternetOpenUrl uses this flag for FTP files and directories.
INTERNET_FLAG_PRAGMA_NOCACHE
Forces the request to be resolved by the origin server, even if a cached copy exists on the proxy. The InternetOpenUrl function (on HTTP and HTTPS requests only) and HttpOpenRequest functions use this flag.
INTERNET_FLAG_RAW_DATA
Returns the data as a GOPHER_FIND_DATA structure when retrieving Gopher directory information, or as a WIN32_FIND_DATA structure when retrieving FTP directory information. If this flag is not specified or if the call was made through a CERN proxy, InternetOpenUrl returns HTML version of the directory. Only the InternetOpenUrl function uses this flag.
INTERNET_FLAG_READ_PREFETCH
This flag is currently disabled.
INTERNET_FLAG_RELOAD
Forces a download of the requested file, object, or directory listing from the origin server, not from the cache. The GopherFindFirstFile, GopherOpenFile, FtpFindFirstFile, FtpGetFile, FtpOpenFile, FtpPutFile, HttpOpenRequest, and InternetOpenUrl functions utilize this flag.
INTERNET_FLAG_RESYNCHRONIZE
Reloads HTTP resources if the resource has been modified since the last time it was downloaded. All FTP and Gopher resources are reloaded. This flag can be used by GopherFindFirstFile, GopherOpenFile, FtpFindFirstFile, FtpGetFile, FtpOpenFile, FtpPutFile, HttpOpenRequest, and InternetOpenUrl.
INTERNET_FLAG_SECURE
Uses secure transaction semantics. This translates to using Secure Sockets Layer/Private Communications Technology (SSL/PCT) and is only meaningful in HTTP requests. This flag is used by HttpOpenRequest and InternetOpenUrl, but this is made redundant if "https://" appears in the URL.
INTERNET_FLAG_TRANSFER_ASCII
Transfers file as ASCII (FTP only). This flag can be used by FtpOpenFile, FtpGetFile, and FtpPutFile.
INTERNET_FLAG_TRANSFER_BINARY
Transfers file as binary (FTP only). This flag can be used by FtpOpenFile, FtpGetFile, and FtpPutFile.
WININET_API_FLAG_ASYNC
Forces asynchronous operations.
WININET_API_FLAG_SYNC
Forces synchronous operations.
WININET_API_FLAG_USE_CONTEXT
Forces the API to use the context value, even if it is set to zero.

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