WSALookupServiceBegin Function

The WSALookupServiceBegin function initiates a client query that is constrained by the information contained within a WSAQUERYSET structure. WSALookupServiceBegin only returns a handle, which should be used by subsequent calls to WSALookupServiceNext to get the actual results.

Syntax

INT WSALookupServiceBegin(
  __in   LPWSAQUERYSET lpqsRestrictions,
  __in   DWORD dwControlFlags,
  __out  LPHANDLE lphLookup
);

Parameter

• lpqsRestrictions [in]
  A pointer to the search criteria. See the Remarks for details.

• dwControlFlags [in]
  A set of flags that controls the depth of the search.

  Supported values for the dwControlFlags parameter are defined in the Winsock2.h header file and can be a combination of the following options.

  Flag	Bedeutung
  LUP_DEEP 0x0001	Queries deep as opposed to just the first level.
  LUP_CONTAINERS 0x0002	Returns containers only.
  LUP_NOCONTAINERS 0x0004	Do not return containers.
  LUP_NEAREST 0x0008	If possible, returns results in the order of distance. The measure of distance is provider specific.
  LUP_RETURN_NAME 0x0010	Retrieves the name as lpszServiceInstanceName.
  LUP_RETURN_TYPE 0x0020	Retrieves the type as lpServiceClassId.
  LUP_RETURN_VERSION 0x0040	Retrieves the version as lpVersion.
  LUP_RETURN_COMMENT 0x0080	Retrieves the comment as lpszComment.
  LUP_RETURN_ADDR 0x0100	Retrieves the addresses as lpcsaBuffer.
  LUP_RETURN_BLOB 0x0200	Retrieves the private data as lpBlob.
  LUP_RETURN_ALIASES 0x0400	Any available alias information is to be returned in successive calls to WSALookupServiceNext, and each alias returned will have the RESULT_IS_ALIAS flag set.
  LUP_RETURN_QUERY_STRING 0x0800	Retrieves the query string used for the request.
  LUP_RETURN_ALL 0x0FF0	A set of flags that retrieves all of the LUP_RETURN_* values.
  LUP_FLUSHPREVIOUS 0x1000	Used as a value for the dwControlFlags parameter in WSALookupServiceNext. Setting this flag instructs the provider to discard the last result set, which was too large for the specified buffer, and move on to the next result set.
  LUP_FLUSHCACHE 0x2000	If the provider has been caching information, ignores the cache, and queries the namespace itself.
  LUP_RES_SERVICE 0x8000	This indicates whether prime response is in the remote or local part of CSADDR_INFO structure. The other part needs to be usable in either case.

   

• lphLookup [out]
  A handle to be used when calling WSALookupServiceNext in order to start retrieving the results set.

Rückgabewert

The return value is zero if the operation was successful. Otherwise, the value SOCKET_ERROR is returned, and a specific error number can be retrieved by calling WSAGetLastError.

Hinweise

The lpqsRestrictions parameter points to a buffer containing a WSAQUERYSET structure. At a minimum, the dwSize member of the WSAQUERYSET must be set to the length of the buffer before calling the WSALookupServiceBegin function. Applications can restrict the query by specifying other members in the WSAQUERYSET.

In most instances, applications interested in only a particular transport protocol should constrain their query by address family and protocol using the dwNumberOfProtocols and lpafpProtocols members of the WSAQUERYSET rather than by specifiying the namespace in the dwNameSpace member.

Information on supported network transport protocols can be retreived using the EnumProtocols, WSAEnumProtocols, WSCEnumProtocols, or WSCEnumProtocols32 function.

It is also possible to constrain the query to a single namespace. For example, a query that only wants results from DNS (not results from the local hosts file and other naming services) would set the dwNameSpace member to NS_DNS. For example, a bluetooth device discovery would set the the dwNameSpace member to NS_BTH.

Applications can also restrict the query to a specific namespace provider by specifying a pointer to the GUID for the provider in the lpNSProviderId member.

Information on namespace providers on the local computer can be retrieved using the WSAEnumNameSpaceProviders, WSAEnumNameSpaceProvidersEx, WSCEnumNameSpaceProviders32, or WSCEnumNameSpaceProvidersEx32 function.

If LUP_CONTAINERS is specified in a call, other restriction values should be avoided. If any are specified, it is up to the name service provider to decide if it can support this restriction over the containers. If it cannot, it should return an error.

Some name service providers can have other means of finding containers. For example, containers might all be of some well-known type, or of a set of well-known types, and therefore a query restriction can be created for finding them. No matter what other means the name service provider has for locating containers, LUP_CONTAINERS and LUP_NOCONTAINERS take precedence. Hence, if a query restriction is given that includes containers, specifying LUP_NOCONTAINERS will prevent the container items from being returned. Similarly, no matter the query restriction, if LUP_CONTAINERS is given, only containers should be returned. If a namespace does not support containers, and LUP_CONTAINERS is specified, it should simply return WSANO_DATA.

The preferred method of obtaining the containers within another container, is the call:

dwStatus = WSALookupServiceBegin(
      lpqsRestrictions,
      LUP_CONTAINERS,
      lphLookup);

This call is followed by the requisite number of WSALookupServiceNext calls. This will return all containers contained immediately within the starting context; that is, it is not a deep query. With this, one can map the address space structure by walking the hierarchy, perhaps enumerating the content of selected containers. Subsequent uses of WSALookupServiceBegin use the containers returned from a previous call.

As mentioned above, a WSAQUERYSET structure is used as an input parameter to WSALookupBegin in order to qualify the query. The following table indicates how the WSAQUERYSET is used to construct a query. When a parameter is marked as (Optional) a NULL pointer can be specified, indicating that the parameter will not be used as a search criteria. See section Query-Related Data Structures for additional information.

Wichtig  In most instances, applications interested in only a particular transport protocol should constrain their query by address family and protocol rather than by namespace. This would allow an application that needs to locate a TCP/IP service, for example, to have its query processed by all available namespaces such as the local hosts file, DNS, and NIS.

Anforderungen

Siehe auch

Bluetooth and WSALookupServiceBegin

EnumProtocols

WSAEnumNameSpaceProviders

WSAEnumNameSpaceProvidersEx

WSAEnumProtocols

WSALookupServiceEnd

WSALookupServiceNext

WSAQUERYSET

WSCEnumProtocols

WSCEnumProtocols32

WSCEnumNameSpaceProviders32

WSCEnumNameSpaceProvidersEx32