NAME¶
Net::DBus::Exporter - Export object methods and signals to the bus
SYNOPSIS¶
# Define a new package for the object we're going
# to export
package Demo::HelloWorld;
# Specify the main interface provided by our object
use Net::DBus::Exporter qw(org.example.demo.Greeter);
# We're going to be a DBus object
use base qw(Net::DBus::Object);
# Ensure only explicitly exported methods can be invoked
dbus_strict_exports;
# Export a 'Greeting' signal taking a stringl string parameter
dbus_signal("Greeting", ["string"]);
# Export 'Hello' as a method accepting a single string
# parameter, and returning a single string value
dbus_method("Hello", ["string"], ["string"]);
# Export 'Goodbye' as a method accepting a single string
# parameter, and returning a single string, but put it
# in the 'org.exaple.demo.Farewell' interface
dbus_method("Goodbye", ["string"], ["string"], "org.example.demo.Farewell");
DESCRIPTION¶
The "Net::DBus::Exporter" module is used to export methods and signals
defined in an object to the message bus. Since Perl is a loosely typed
language it is not possible to automatically determine correct type
information for methods to be exported. Thus when sub-classing
Net::DBus::Object, this package will provide the type information for methods
and signals.
When importing this package, an optional argument can be supplied to specify the
default interface name to associate with methods and signals, for which an
explicit interface is not specified. Thus in the common case of objects only
providing a single interface, this removes the need to repeat the interface
name against each method exported.
SCALAR TYPES¶
When specifying scalar data types for parameters and return values, the
following string constants must be used to denote the data type. When values
corresponding to these types are (un)marshalled they are represented as the
Perl SCALAR data type (see perldata).
- "string"
- A UTF-8 string of characters
- "int16"
- A 16-bit signed integer
- "uint16"
- A 16-bit unsigned integer
- "int32"
- A 32-bit signed integer
- "uint32"
- A 32-bit unsigned integer
- "int64"
- A 64-bit signed integer. NB, this type is not supported by many builds of
Perl on 32-bit platforms, so if used, your data is liable to be truncated
at 32-bits.
- "uint64"
- A 64-bit unsigned integer. NB, this type is not supported by many builds
of Perl on 32-bit platforms, so if used, your data is liable to be
truncated at 32-bits.
- "byte"
- A single 8-bit byte
- "bool"
- A boolean value
- "double"
- An IEEE double-precision floating point
COMPOUND TYPES¶
When specifying compound data types for parameters and return values, an array
reference must be used, with the first element being the name of the compound
type.
- ["array", ARRAY-TYPE]
- An array of values, whose type os "ARRAY-TYPE". The
"ARRAY-TYPE" can be either a scalar type name, or a nested
compound type. When values corresponding to the array type are
(un)marshalled, they are represented as the Perl ARRAY data type (see
perldata). If, for example, a method was declared to have a single
parameter with the type, ["array", "string"], then
when calling the method one would provide a array reference of strings:
$object->hello(["John", "Doe"])
- ["dict", KEY-TYPE, VALUE-TYPE]
- A dictionary of values, more commonly known as a hash table. The
"KEY-TYPE" is the name of the scalar data type used for the
dictionary keys. The "VALUE-TYPE" is the name of the scalar, or
compound data type used for the dictionary values. When values
corresponding to the dict type are (un)marshalled, they are represented as
the Perl HASH data type (see perldata). If, for example, a method was
declared to have a single parameter with the type ["dict",
"string", "string"], then when calling the method one
would provide a hash reference of strings,
$object->hello({forename => "John", surname => "Doe"});
- ["struct", VALUE-TYPE-1, VALUE-TYPE-2]
- A structure of values, best thought of as a variation on the array type
where the elements can vary. Many languages have an explicit name
associated with each value, but since Perl does not have a native
representation of structures, they are represented by the LIST data type.
If, for exaple, a method was declared to have a single parameter with the
type ["struct", "string", "string"],
corresponding to the C structure
struct {
char *forename;
char *surname;
} name;
then, when calling the method one would provide an array refernce with the
values orded to match the structure
$object->hello(["John", "Doe"]);
MAGIC TYPES¶
When specifying introspection data for an exported service, there are a couple
of so called "magic" types. Parameters declared as magic types are
not visible to clients, but instead their values are provided automatically by
the server side bindings. One use of magic types is to get an extra parameter
passed with the unique name of the caller invoking the method.
- "caller"
- The value passed in is the unique name of the caller of the method. Unique
names are strings automatically assigned to client connections by the bus
daemon, for example ':1.15'
- "serial"
- The value passed in is an integer within the scope of a caller, which
increments on every method call.
ANNOTATIONS¶
When exporting methods, signals & properties, in addition to the core data
typing information, a number of metadata annotations are possible. These are
specified by passing a hash reference with the desired keys as the last
parameter when defining the export. The following annotations are currently
supported
- no_return
- Indicate that this method does not return any value, and thus no reply
message should be sent over the wire, likewise informing the clients not
to expect / wait for a reply message
- deprecated
- Indicate that use of this method/signal/property is discouraged, and it
may disappear altogether in a future release. Clients will typically print
out a warning message when a deprecated method/signal/property is
used.
- param_names
- An array of strings specifying names for the input parameters of the
method or signal. If omitted, no names will be assigned.
- return_names
- An array of strings specifying names for the return parameters of the
method. If omitted, no names will be assigned.
METHODS¶
- dbus_method($name, $params, $returns, [\%annotations]);
- dbus_method($name, $params, $returns, $interface, [\%annotations]);
- Exports a method called $name, having parameters whose types are defined
by $params, and returning values whose types are defined by $returns. If
the $interface parameter is provided, then the method is associated with
that interface, otherwise the default interface for the calling package is
used. The value for the $params parameter should be an array reference
with each element defining the data type of a parameter to the method.
Likewise, the $returns parameter should be an array reference with each
element defining the data type of a return value. If it not possible to
export a method which accepts a variable number of parameters, or returns
a variable number of values.
- dbus_no_strict_exports();
- If a object is using the Exporter to generate DBus introspection data, the
default behaviour is to only allow invocation of methods which have been
explicitly exported.
To allow clients to access methods which have not been explicitly exported,
call "dbus_no_strict_exports". NB, doing this may be a security
risk if you have methods considered to be "private" for internal
use only. As such this method should not normally be used. It is here only
to allow switching export behaviour to match earlier releases.
- dbus_property($name, $type, $access, [\%attributes]);
- dbus_property($name, $type, $access, $interface, [\%attributes]);
- Exports a property called $name, whose data type is $type. If the
$interface parameter is provided, then the property is associated with
that interface, otherwise the default interface for the calling package is
used.
- dbus_signal($name, $params, [\%attributes]);
- dbus_signal($name, $params, $interface, [\%attributes]);
- Exports a signal called $name, having parameters whose types are defined
by $params. If the $interface parameter is provided, then the signal is
associated with that interface, otherwise the default interface for the
calling package is used. The value for the $params parameter should be an
array reference with each element defining the data type of a parameter to
the signal. Signals do not have return values. It not possible to export a
signal which has a variable number of parameters.
EXAMPLES¶
- No parameters, no return values
- A method which simply prints "Hello World" each time its called
sub Hello {
my $self = shift;
print "Hello World\n";
}
dbus_method("Hello", [], []);
- One string parameter, returning an boolean value
- A method which accepts a process name, issues the killall command on it,
and returns a boolean value to indicate whether it was successful.
sub KillAll {
my $self = shift;
my $processname = shift;
my $ret = system("killall $processname");
return $ret == 0 ? 1 : 0;
}
dbus_method("KillAll", ["string"], ["bool"]);
- One list of strings parameter, returning a dictionary
- A method which accepts a list of files names, stats them, and returns a
dictionary containing the last modification times.
sub LastModified {
my $self = shift;
my $files = shift;
my %mods;
foreach my $file (@{$files}) {
$mods{$file} = (stat $file)[9];
}
return \%mods;
}
dbus_method("LastModified", ["array", "string"], ["dict", "string", "int32"]);
- Annotating methods with metdata
- A method which is targeted for removal, and also does not return any value
sub PlayMP3 {
my $self = shift;
my $track = shift;
system "mpg123 $track &";
}
dbus_method("PlayMP3", ["string"], [], { deprecated => 1, no_return => 1 });
Or giving names to input parameters:
sub PlayMP3 {
my $self = shift;
my $track = shift;
system "mpg123 $track &";
}
dbus_method("PlayMP3", ["string"], [], { param_names => ["track"] });
AUTHOR¶
Daniel P. Berrange <dan@berrange.com>
COPYRIGHT¶
Copright (C) 2004-2011, Daniel Berrange.
SEE ALSO¶
Net::DBus::Object, Net::DBus::Binding::Introspector