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Retired Document

Important: Support for DirectoryService plug-ins has been deprecated and will be removed in a future release.

A new architecture was introduced in OS X v10.9 to allow the creation of native Open Directory modules. Unlike DirectoryService, opendirectoryd uses modules implemented as a standalone process that uses XPC to communicate with opendirectoryd. Implementing a module as an XPC service ensures a private address space and improves security and reliability, because modules cannot crash another module or opendirectoryd.

Client Side Buffer Parsing

Open Directory provides standard data buffer parsing for a tDataBuffer returned by the plug-in serviced functions dsGetRecordList, dsDoAttributeValueSearch, and dsDoAttributeValueSearchWithData if and only if the buffer was built using the standard format, known as Client Side Buffer Parsing (CSBP) described in this section.

CSBP reduces round trip Mach and TCP message traffic between the client and the server that would otherwise require the passing of the entire tDataBuffer. Thus, CSBP leads to a considerable performance improvement in servicing calls to dsGetRecordEntry, dsGetAttributeEntry, and dsGetAttributeValue, which have to extract particular data points such as attribute values out of a tDataBuffer.

There are two CSBP standards: StdA and StdB. StdB was the first format and it is still supported. StdA allows for larger attributes and is the recommended format.

Table 12-1 lists the order of the overall data block holding x number of records.

**Table 12-1** Format of a StdA and StdB data block
Number of Bytes	Description
4	ulong:: tag describing the data block; value is `STDA` or `STDB`
4	ulong:: count of records contained in this data block
4	ulong:: offset in bytes to the start of the first record block
4	ulong:: offset in bytes to the start of the second record block
...
4	ulong:: offset in bytes to the start of the last record block
4	ulong:: tag describing end of offsets; value is `ENDT`
...	empty space until the start of the last record block; that is, record blocks are packed into the buffer starting at the end of the data block
4	ulong:: length in bytes of last record block
#	last record block
...
4	ulong:: length in bytes of first record block
#	first record block

Table 12-2 lists the order of a StdA single record block holding y complete attribute blocks.

**Table 12-2** Format of a StdA single record block
Number of Bytes	Description
2	ushort:: length of record type string
n	UTF-8[n]:: record type string
2	ushort:: length of record name string
m	UTF-8[m]:: record name string
2	ushort:: number of attributes in this record block
4	ulong:: length in bytes of first attribute block
#	first attribute block for this record block
....
4	ulong:: length in bytes of last attribute block
#	last attribute block for this record block

Table 12-3 lists the order of a StdA single attribute block holding z values (that is, all of the attribute’s values).

**Table 12-3** Format of a StdA single attribute block
Number of Bytes	Description
2	ushort:: length of attribute name
r	UTF-8[r]:: attribute name string
2	ushort:: number of attribute values in this attribute block
4	ulong:: length of first attribute value
s	byte[s]:: first attribute value for this attribute type
....
4	ulong:: length of last attribute value
t	byte[t]:: last attribute value for this attribute type

Table 12-4 lists the order of a StdB single record block holding y complete attribute blocks.

**Table 12-4** Format of a StdB single record block
Number of Bytes	Description
2	ushort:: length of record type string
n	UTF-8[n]:: record type string
2	ushort:: length of record name string
m	UTF-8[m]:: record name string
2	ushort:: number of attributes in this record block
2	ushort:: length in bytes of first attribute block
#	first attribute block for this record block
....
2	ushort:: length in bytes of last attribute block
#	last attribute block for this record block

Table 12-5 lists the order of a StdB single attribute block holding z values (that is, all of the attribute’s values).

**Table 12-5** Format of a StdB single attribute block
Number of Bytes	Description
2	ushort:: length of attribute name
r	UTF-8[r]:: attribute name string
2	ushort:: number of attribute values in this attribute block
2	ushort:: length of first attribute value
s	byte[s]:: first attribute value for this attribute type
....
2	ushort:: length of last attribute value
t	byte[t]:: last attribute value for this attribute type

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