Node dbus-native - node.js

Question

The documentation for node module dbus-native is weak, and the none of the many examples apply to my use case, which seems like it ought to be simple.
My problem is trying to make a simple method call into the "connman" network manager. I can make a request (invoking GetProperties method) just fine, and get a complex structure back and generally figure out how to get data out of it. But when I try to send something back with SetProperty, I just can't figure out how to get my data into the form it wants.
There's not really any documentation about how to translate to and from DBus's type system and node's. I gathered from source that variant types are arrays with signature and value, e.g., [ 's', 'string ], but no matter how I try to massage the data I'm trying to send to SetProperty, I get an "Invalid struct data" error.
The SetProperty method I'm trying to call has an argument signature "sv"--name, value. The particular property I'm trying to set has a value with is itself (as far as I can determine--there's precious little documentation on that side as well) an "a{sv}". that is,property is a hash of property names and values. My initial attempt as calling this function was:
var sysbus = require('dbus-native').systemBus();
sysbus.invoke({
path: '/net/connman/service/ethernet_1cba8cfa0e57_cable',
destination: 'net.connman',
'interface': 'net.connman.Service',
member: 'SetPropertry',
signature: 'sv',
body: [
'IPv4.Configuration', [
'a{sv}',
{ 'Method': [ 's', 'dhcp' ] }
]
],
type: dbus.messageType.methodCall
}, function (err, res) {
// etc...
});
This gives me the "Invalid struct data" error. I've tried man other ways to wrap the data in arrays, hashes, etc., and just can't seem to find the right answer. I'm trying to emulate this working Python code:
import dbus
bus = dbus.SystemBus()
service = dbus.Interface(bus.get_object("net.connman",
"/net/connman/service/ethernet_1cba8cfa0e57_cable",
"net.connman.Service");
conf = { "Method": make_string_variant("dhcp") }
service.SetProperty("IPv4.Configuration", conf);
Any ideas?

Answer 1

I recently started using dbus-native for connman and also had problems with all the nested arrays. I'll be improving the marshaling/unmarshaling in the fork of the project at https://github.com/Digisoft-tv/node-dbus - you might want to have a look. Hopefully my changes will be accepted up-stream.
Anyway, to get it working now, the format of the parameters you need to pass in is as below:
mgr.CreateSession([ [ 'key', [ 's', 'value' ] ], [ 'key2', [ 'i', 2 ] ] ], '/object/path', function(error, response) {
if (error) {
return console.error('SetProperty error:', error);
}
console.info('SetProperty response', response);
});
The outermost array is the "object" (ARRAY of dict entries).
Each nested array holds a key-value pair (DICT ENTRY). key at index 0 and value at index 1.
The values is a variant, which is always encoded as an array, with "signature" at index 0 and the actual value at index 1.
Hope it helps.

Answer 2

The correct way to encode 'a{sv}' is [ ['string', ['signature', 'value']], ... ]
Arrays ( a ) are encoded as normal JS arrays as well as structs / hashes ( () / {} ). I'll probably add shortcut to allow JS object to be used in place of a{sv} but at the moment input has to be quite verbose.
var sysbus = require('dbus-native').systemBus();
sysbus.invoke({
path: '/net/connman/service/ethernet_1cba8cfa0e57_cable',
destination: 'net.connman',
'interface': 'net.connman.Service',
member: 'SetPropertry',
signature: 'sv',
body: [
'IPv4.Configuration', [
'a{sv}',
[ // a
[ // {
'Method', [ 's', 'dhcp' ] // sv
]
]
]
],
type: dbus.messageType.methodCall
}, function (err, res) {
// etc...
});