Implementing a DBus interface exposing an object tree to clients

[Lurkki]

I want to implement a DBus API where the client is able to get a hierarchy of devices and their properties as follows:

Device 0
    Some Category
        Property 1
        Property 2
Device 1
    Some Other Category
        Subcategory
            Property 1

is there a way to access the objects as a tree in the client without manually parsing the relationships from the object paths?

[SGaist]

Hi,

I am not sure I am following you on this. How would you like to access the data of your data tree ?

[Lurkki]

I'd basically like to get the object located at /DBusInterface/devices and use its subtrees for presentation, something like:

Device d = getRootDeviceFromDbus();
constructItemModel(d); // Construct item model from root device recursively

[SGaist]

So you are missing the construct model method ?

[Lurkki]

I'm trying to find out if there's a way to get the object tree without manually parsing all the object paths

[SGaist]

If the structure is fixed. You can create a model on top of these objects.

[Lurkki]

The structure isn't fixed, which is the entire reason for needing this

[SGaist]

Ok, but what would you get from your DBus endpoint ?

[Lurkki]

Ended up writing the following code that parses a list of paths into a tree

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{
    auto central = new QWidget;
    auto lo = new QVBoxLayout;

    auto view = new QTreeView;
    auto model = new QStandardItemModel;

    auto root = model->invisibleRootItem();

    QStringList pathList;

    pathList << "/dev" << "/dev/gpu" << "/dev/gpu2" << "/dev/gpu/fans/0" << "/dev/gpu2/powerlim";

    struct Node {
        QString name;
        QVector <Node*> children;
    };


    auto lowestAncestor = [=](QStringList tokens, Node *root, int *tokenIndex) {
        int i = 0;
        bool flag = false;
        Node *node_it = root;
        while (node_it && i < tokens.length()) {
            for (auto node : node_it->children) {
                if (node->name.compare(tokens[i]) == 0) {
                    i++;
                    flag = true;
                    node_it = node;
                    break;
                }
            }
            if (!flag) {
                break;
            }
            flag = false;
        }
        *tokenIndex = i;
        return node_it;
    };

    std::function<void (QString, QStringList, Node*)> addNode;
    addNode = [=, &addNode](QString path, QStringList tokens, Node *node) {
        // Call this function until lowestAncestor.name == tokens.last()
        int i;
        auto n = lowestAncestor(tokens, node, &i);
        if (tokens.last().compare(n->name) != 0) {
            auto new_ = new Node;
            new_->name = tokens[i];

            n->children.append(new_);
            addNode(path, tokens, node);
        }
    };

    Node *rootNode = new Node;

    for (auto &path : pathList) {
        addNode(path, path.split(QRegExp("/+"), QString::SkipEmptyParts), rootNode);
    }

    std::function <void(QStandardItem*, Node*)> traverse;
    traverse = [=, &traverse](QStandardItem *item, Node *node) {
        auto newItem = new QStandardItem;
        newItem->setData(node->name, Qt::DisplayRole);

        item->appendRow(newItem);
        for (auto node : node->children) {
            traverse(newItem, node);
        }
    };

    for (auto n : rootNode->children) {
        traverse(root, n);
    }

    view->setModel(model);

    lo->addWidget(view);

    central->setLayout(lo);
    setCentralWidget(central);
}