3.2.4.29 R_DhcpEnumClasses (Opnum 28)

The R_DhcpEnumClasses method enumerates user classes or vendor classes configured for the DHCP server. The caller of this function can free the memory pointed to by ClassInfoArray and Classes by calling the function midl_user_free (section 3).

 DWORD R_DhcpEnumClasses(
   [in, unique, string] DHCP_SRV_HANDLE ServerIpAddress,
   [in] DWORD ReservedMustBeZero,
   [in, out] DHCP_RESUME_HANDLE* ResumeHandle,
   [in] DWORD PreferredMaximum,
   [out] LPDHCP_CLASS_INFO_ARRAY* ClassInfoArray,
   [out] DWORD* nRead,
   [out] DWORD* nTotal
 );

ServerIpAddress: The IP address/host name of the DHCP server. This parameter is unused.

ReservedMustBeZero: This is of type DWORD and is reserved for future use. Currently it is not used, and any value set to this parameter will not affect the behavior of this method.

ResumeHandle: This is a pointer of type DHCP_RESUME_HANDLE (section 2.2.1.2.6) that identifies the enumeration operation. Initially, this value MUST be set to zero, with a successful call returning the handle value used for subsequent enumeration requests. For example, if PreferredMaximum is set to 100, and 200 classes are stored on the DHCP server, the resume handle can be used after the first 100 classes are retrieved to obtain the next 100 on a subsequent call, and so forth.

PreferredMaximum: This is of type DWORD, specifying the preferred maximum number of bytes to be returned. If the number of bytes required in memory for the remaining unenumerated classes is less than the PreferredMaximum value, then all the classes for the DHCP server are returned. To retrieve all the classes defined on the DHCP server, 0xFFFFFFFF is specified.

ClassInfoArray: This is a pointer of type LPDHCP_CLASS_INFO_ARRAY in which information of all the classes defined on the DHCP server is retrieved.

nRead: This is a pointer to a DWORD value that specifies the number of classes returned in ClassInfoArray. The caller MUST allocate memory for this parameter equal to the size of data type DWORD.

nTotal: This is a pointer to a DWORD value that specifies the number of classes defined on the DHCP server that have not yet been enumerated. The caller MUST allocate memory for this parameter equal to the size of data type DWORD.

Return Values: A 32-bit unsigned integer value that indicates return status. A return value ERROR_SUCCESS (0x00000000) indicates that the operation was completed successfully, else it contains a Win32 error code, as specified in [MS-ERREF]. This error code value can correspond to a DHCP-specific failure, which takes a value between 20000 and 20099, or any generic failure.

Return value/code

Description

0x00000000

ERROR_SUCCESS

The call was successful.

0x000000EA

ERROR_MORE_DATA

There are more elements available to enumerate.

0x00000103

ERROR_NO_MORE_ITEMS

There are no more elements left to enumerate.

The opnum field value for this method is 28.

When processing this call, the DHCP server MUST do the following:

  • If the parameters ClassInfoArray, ResumeHandle, nRead, and nTotal are NULL, return ERROR_INVALID_PARAMETER.

  • Validate if this method is authorized for read access per section 3.5.4. If not, return the error ERROR_ACCESS_DENIED.

  • Retrieve all the entries in server ADM element DHCPv4ClassDefList.

  • If the ResumeHandle parameter points to 0x00000000, the enumeration MUST start from the first entry of the DHCPv4ClassDefList.

  • If the ResumeHandle parameter points to a nonzero value, the server MUST continue enumeration based on the value of ResumeHandle. If the ResumeHandle parameter is greater than or equal to the number of entries in the DHCPv4ClassDefList ADM element, then return ERROR_NO_MORE_ITEMS.

  • If the PreferredMaximum parameter is 0 and the number of DHCPv4ClassDef entries retrieved is greater than 0, then ERROR_MORE_DATA is returned.

  • If PreferredMaximum parameter is 0 and the number of DHCPv4ClassDef entries retrieved is 0, then ERROR_NO_MORE_ITEMS is returned.

  • The PreferredMaximum parameter specifies the maximum number of bytes that the server can allocate and return to the caller containing the data related to the classes. If the PreferredMaximum parameter is unable to hold all the entries being retrieved, then the server must store as many entries that will fit into the ClassInfoArray parameter and return ERROR_MORE_DATA.

  • Allocate the memory for DHCP_CLASS_INFO_ARRAY (section 2.2.1.2.76) and for the total number of classes type DHCP_CLASS_INFO (section 2.2.1.2.75) from ResumeHandle to the end of the option list.

  • Read the entries information in the ADM element DHCPv4ClassDef starting from the index specified by ResumeHandle to the end of the DHCPv4ClassDefList ADM element, copy it in the allocated memory, and return it to the caller until the copied data length is less than PreferredMaximum.

  • Fill the number of read DHCPv4ClassDef entries in nRead and the number of DHCPv4ClassDef entries in the DHCPv4ClassDefList that have not been enumerated in nTotal. Set the ResumeHandle to the index of the next DHCPv4ClassDef entry to be read.

Exceptions Thrown: No exceptions are thrown beyond those thrown by the underlying RPC protocol [MS-RPCE].