xref: /netbsd-src/common/lib/libprop/proplib.3 (revision a792b8435ef0aa524ea0324495e533001a8cb8e6)

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.\" by Jason R. Thorpe.
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.Dd June 2, 2020
.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.
This external representation is 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
.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 .
.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
The
.Nm
.Sq number
object type differs from the Apple XML property list format in the following
ways:
.Bl -bullet
.It
The external representation is in base 16, not base 10.
.Nm
is able to parse base 8, base 10, and base 16
.Sq integer
elements.
.It
Internally, integers are always stored as unsigned numbers
.Pq uintmax_t .
Therefore, the external representation will never be negative.
.It
Because floating point numbers are not supported,
.Sq real
elements from an Apple XML property list will not be parsed.
.El
.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.