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Dd April 20, 2025
Dt PROPLIB 3
Os
Sh NAME
Nm proplib
Nd property container object library
Sh LIBRARY
Lb libprop
Sh SYNOPSIS
In prop/proplib.h
Sh DESCRIPTION
The
Nm
library provides an abstract interface for creating and manipulating
property lists.
Property lists have object types for boolean values, opaque data, numbers,
and strings.
Structure is provided by the array and dictionary collection types.
Pp
Property lists can be passed across protection boundaries by translating
them to an external representation.
There are two formats availavble for external representation:
Bl -bullet
It
An XML document whose format is described by the following DTD:
Bd -literal -offset indent
Lk http://www.apple.com/DTDs/PropertyList-1.0.dtd
Ed
It
A JSON document whose format is described by RFC 8259.
El
Pp
Property container objects are reference counted.
When an object is created, its reference count is set to 1.
Any code that keeps a reference to an object, including the collection
types
Pq arrays and dictionaries ,
must
Dq retain
the object
Pq increment its reference count .
When that reference is dropped, the object must be
Dq released
Pq reference count decremented .
When an object's reference count drops to 0, it is automatically freed.
Pp
The rules for managing reference counts are very simple:
Bl -bullet
It
If you create an object and do not explicitly maintain a reference to it,
you must release it.
It
If you get a reference to an object from other code and wish to maintain
a reference to it, you must retain the object.
You are responsible for
releasing the object once you drop that reference.
It
You must never release an object unless you create it or retain it.
El
Pp
Object collections may be iterated by creating a special iterator object.
Iterator objects are special; they may not be retained, and they are
released using an iterator-specific release function.
Sh SEE ALSO
Xr prop_array 3 ,
Xr prop_array_util 3 ,
Xr prop_bool 3 ,
Xr prop_data 3 ,
Xr prop_dictionary 3 ,
Xr prop_dictionary_util 3 ,
Xr prop_number 3 ,
Xr prop_object 3 ,
Xr prop_send_ioctl 3 ,
Xr prop_send_syscall 3 ,
Xr prop_string 3
Sh HISTORY
The
Nm
property container object library first appeared in
Nx 4.0 .
Support for the JSON serialization format was added in
Nx 11.0 .
Sh CAVEATS
Nm
does not have a
Sq date
object type, and thus will not parse
Sq date
elements from an Apple XML property list.
Pp
Nm
does not have a
Sq null
object type, and thus will not parse
Sq null
elements from a JSON document.
Pp
The
Nm
Sq number
object type differs from the Apple XML property list format in the following
ways:
Bl -bullet
It
The external representation for unsigned numbers is in base 16, not base 10.
Nm
is able to parse base 8, base 10, and base 16
Sq integer
elements.
Signed numbers are represented in base 10.
It
Nm
does not support floating point numbers, so
Sq real
elements from an Apple XML property list will not be parsed.
El
Pp
Similarly,
Nm
does not parse floating point numbers
Pq as described in RFC 8259
in JSON documents.
For JSON documents, all numbers are represented in base 10.
Pp
JSON does not have an opaque data element that is functionally equivalent
to the
Sq data
elements in XML property lists.
As such, a property list containing
Sq data
objects cannot be externalized into a JSON document.
Pp
In order to facilitate use of
Nm
in kernel, standalone, and user space environments, the
Nm
parser is not a real XML parser.
It is hard-coded to parse only the property list external representation.

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