The DATA_EXTENSION_PREFIX structure contains a data component size and type. The structure of DATA_EXTENSION_PREFIX is as follows.

 typedef struct _DATA_EXTENSION_PREFIX {
   ULONG Size;
   LONG Type;
 } DATA_EXTENSION_PREFIX,
  *PDATA_EXTENSION_PREFIX;

Size: A 32-bit, unsigned integer that specifies the size of the data component, including this prefix.

Type: A 32-bit, unsigned integer that specifies the type of the data component. It MUST be one of the following values.

Value	Meaning
0x00000000	Terminates a data extension record. MUST NOT be used.
0x00000001	Data checksum record using an MD5 hash.
0x00000002	Data retry time-out record.