Name Resolution Data Structures
There are several important data structures that are used extensively
throughout the name resolution functions. These are described below.
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 since it contains pointers to several other
structures, some of which reference still other structures. The relationship between
WSAQUERYSET and the structures it references is illustrated as follows:
WSAQUERYSET and Friends
Within the WSAQUERYSET structure, most of the fields are self explanatory, but
some deserve additional explanation. The
dwSize field must always be filled in with sizeof(WSAQUERYSET), as this is used by
name space providers to detect and adapt to different versions of the
WSAQUERYSET structure that may appear over time.
The
dwOutputFlags field is used by a name space provider to provide additional information
about query results. For details, see
WSALookupServiceNext.
The
WSAECOMPARATOR structure referenced by
lpversion is used for both query constraint and results. For queries, the
dwVersion field indicates the desired version of the service. The
ecHow field is an enumerated type which specifies how the comparison will be made.
The choices are COMP_EQUALS which requires that an exact match in version
occurs, or COMP_NOTLESS which specifies that the service's version number be no less
than the value of
dwVersion.
The interpretation of
dwNameSpace and
lpNSProviderId depends upon how the structure is being used and is described further in the
individual function descriptions that utilize this structure.
The
lpszContext field applies to hierarchical name spaces, and specifies the starting point
of a query or the location within the hierarchy where the service resides. The
general rules are:
- A value of NULL, blank ("") will start the search at the default context.
- A value of "\" starts the search at the top of the name space.
- 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 name
space specific. If
dwNameSpace is NS_ALL, then only "" or "\" should be passed as the context since these
are recognized by all name spaces.
The
lpszQueryString field is used to supply additional, name space-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, since protocol values only have meaning within the context of an address
family.
The array of
CSADDR_INFO structure referenced by
lpcsaBuffer contain all of the information needed to 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 fields 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 which
contain a series of parameters that apply to specific name spaces.
Class Info Data Structures
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. This is the string that will be returned by
WSAGetServiceClassNameByServiceClassId.
The
lpClassInfos field in the WSASERVICECLASSINFO structure references an array of
WSANSCLASSINFO structures, each of which supplies a named and typed parameter that applies
to a specified name space. Examples of values for the
lpszName field include: "SapId", "TcpPort", "UdpPort", etc. These strings are
generally specific to the name space identified in
dwNameSpace. Typical values for
dwValueType might be REG_DWORD, REG_SZ, etc. The
dwValueSize field indicates the length of the data item pointed to by
lpValue.
The entire collection of data represented in a WSASERVICECLASSINFO structure
is provided to each name space provider when
WSAInstallServiceClass is invoked. Each individual name space provider then sifts through the list
of WSANSCLASSINFO structures and retain the information applicable to it.
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