Name Resolution Data Structures (Windows Embedded CE 6.0)
1/6/2010
Winsock provides a set of structures that are used extensively throughout the name resolution functions.
Query-Related Data Structures
The WSAQUERYSET structure is used to form queries for WSALookupServiceBegin, and used to deliver query results for WSALookupServiceNext. It is a complex structure because it contains pointers to several other structures, some of which reference even more structures.
Within the WSAQUERYSET structure, most of the parameters are self explanatory, but some deserve additional explanation. The dwSize parameter must always be completed with sizeof(WSAQUERYSET), because this is used by namespace providers to detect and adapt to different versions of the WSAQUERYSET structure that may appear over time.
The dwOutputFlags parameter is used by a namespace provider to provide additional information about query results. For more information, see WSALookupServiceNext.
The WSAECOMPARATOR structure referenced by lpversion is used for both query constraint and results. For queries, the dwVersion parameter indicates the desired version of the service. The ecHow parameter is an enumerated type that specifies how the comparison can be made. The choices are COMP_EQUALS, which requires that an exact match in version occur, or COMP_NOTLESS, which requires that the service's version number be no less than the value of dwVersion.
The lpszContext parameter applies to hierarchical namespaces, and specifies the starting point of a query or the location within the hierarchy where the service resides. The following general rules apply:
- A value of NULL, blank ("") starts the search at the default context.
- A value of "\" starts the search at the top of the namespace.
- Any other value starts the search at the designated point.
Providers that do not support containment may return an error if anything other than "" or "\" is specified. Providers that support limited containment, such as groups, should accept "", '\", or a designated point. Contexts are namespace specific. If dwNameSpace is NS_ALL, then only "" or "\" should be passed as the context because these are recognized by all namespaces.
The lpszQueryString parameter is used to supply additional, namespace-specific query information such as a string describing a well-known service and transport protocol name, as in "FTP/TCP".
The AFPROTOCOLS structure referenced by lpafpProtocols is used for query purposes only, and supplies a list of protocols to constrain the query. These protocols are represented as address family, protocol pairs because protocol values only have meaning within the context of an address family.
The array of CSADDR_INFO structure referenced by lpcsaBuffer contains all of the information needed for either a service to use in establishing a listen, or a client to use in establishing a connection to the service. The LocalAddr and RemoteAddr parameters both directly contain a SOCKET_ADDRESS structure. A service would create a socket using the tuple (LocalAddr.lpSockaddr->sa_family, iSocketType, iProtocol). It would bind the socket to a local address using LocalAddr.lpSockaddr, and LocalAddr.lpSockaddrLength. The client creates its socket with the tuple (RemoteAddr.lpSockaddr->sa_family, iSocketType, iProtocol), and uses the combination of RemoteAddr.lpSockaddr, and RemoteAddr.lpSockaddrLength when making a remote connection.
Service Class Data Structures
When a new service class is installed, a WSASERVICECLASSINFO structure must be prepared and supplied. This structure also consists of substructures that contain a series of parameters that apply to specific namespaces.
For each service class, there is a single WSASERVICECLASSINFO structure. Within the WSASERVICECLASSINFO structure, the service class unique identifier is contained in lpServiceClassId, and an associated display string is referenced by lpServiceClassName. The lpClassInfos parameter in the WSASERVICECLASSINFO structure references an array of WSANSCLASSINFO structures, each of which supplies a named and typed parameter that applies to a specified namespace. Examples of values for the lpszName parameter include SapId, TcpPort, UdpPort, and so on. These strings are generally specific to the namespace identified in dwNameSpace. Typical values for dwValueType might be REG_DWORD and REG_SZ. The dwValueSize parameter indicates the length of the data item pointed to by lpValue.