Possible to get QDomElement from QXmlStreamWriter? - c++

I'm writing a small XMPP server using qxmpp. Now I want to create a QXmppStanza and present it (as if a client had sent it) to the server and my plugins using
void QXmppServer::handleElement(const QDomElement &element)
This function requires a QDomElement and not a QXmppStanza. The only XML realted function I found in QXmppStanza and its derived classes (besides parse(...) ) is the function
void toXml(QXmlStreamWriter *writer)
I don't have experience with XML handling in qt yet, so is there a more performant way than writing the XML to a string/ByteArray, use it as input to create a new QDomElement and return its documentElement?

After doing some further research I have to accept it is not possible.
As stated in QDomDocument's documentation I always require a QDomDocument in order to work with a QDomElement (and other nodes):
Since elements, text nodes, comments, processing instructions, etc., cannot exist outside the context of a document (...)
The QXmlStreamWriter doesn't have a QDomDocument, so I really have to create a QDomDocument (which of course must live as long I want to work with the element) and then parse the text (QDomDocument::setContent).

I had a similar issue and was able to convert from a stream to a DOM element by doing something similar to what is shown below.
The first step is to stream to a byte array.
QByteArray data;
QXmlStreamWriter writer(&data);
object->toXml(&writer);
The second step is to set the content of a DOM document. The document's document element should be the DOM element you need.
QDomDocument temp;
if(temp.setContent(data))
QDomElement element = temp.documentElement(); // do whatever you want with this element

Related

Can I set the child of an object to be an object defined separetely in PugiXML?

I want to configure a device using an XML file and was thinking that I can make the individual pugi::xml_nodes first with the values I need and later on make them children of a document or some parent node. However, I seem to be doing something wrong.
Example that works:
#include "pugixml.hpp"
int main(){
pugi::xml_document xml;
pugi::xml_node configRecord = xml.append_child("configrecord");
pugi::xml_node configGroup = configRecord.append_child("configgroup");
configGroup.append_attribute("name") = "ftp server";
}
This works because I first create the parent document and then start branching by adding children. I was thinking that I can first make the node objects, store them into an array and parse that array to add them to the document. But this doesn't work.
#include "pugixml.hpp"
int main(){
pugi::xml_node myNode;
myNode.set_name("value");
myNode.append_child(pugi::node_pcdata).set_value("enable");
pugi::xml_document docu;
docu.set_name("document");
docu.child(myNode); // <- error here, cannot add child to document
}
Can I somehow use the strategy I was planning to or am I constrained to only adding children to an existing parent?
pugixml documentation states that pugi::xml_node is a non-owning pointer to actual node data stored in a pugi::xml_document object:
xml_node is the handle to document node; it can point to any node in
the document, including the document node itself. There is a common
interface for nodes of all types; the actual node type can be queried
via the xml_node::type() method. Note that xml_node is only a handle
to the actual node, not the node itself
Nodes and attributes do not exist without a document tree, so you
can’t create them without adding them to some document.
It seems to me that your code doesn't throw errors when you try to manipulate myNode because default-constructed "null" nodes silently consume operations on them to make chaining easier:
all operations are defined on empty nodes; generally the operations
don’t do anything and return empty nodes/attributes or empty strings
as their result [...] This is useful for chaining calls

rapidXML, corrupted memory when traversing DOM tree

Don't understand what is going on with the attribute's memory and rapidXML.
A function encapsulates the xml parsing, if success, returns a reference to the root node, when calling the traverse DOM tree inside this function I get the correct data stored in an xml file.
typedef rapidxml::xml_node<>* Node;
...
Node Load()
{
Node pRootNode = NULL;
// read file stream in bytes
...
std::vector<char> xmlCopy(bytes.begin(), bytes.end());
xmlCopy.push_back('\0');
rapidxml::xml_document<> doc;
try
{
doc.parse<rapidxml::parse_declaration_node | rapidxml::parse_no_data_nodes>(&bytes[0]);
pRootNode = doc.first_node();
...
TraverseDOMTree(pRootNode);
}
return pRootNode;
}
TraverseDOMTree prints all attributes and node names as expected.
Later, obviously outside the scope of Load, pRootNode will be used to query values from the DOM three, this doesn't work.
For testing purposes calling TraverseDOMTree, which perfectly worked, now prints attribute's garbage values. I can assume the DOM tree is still there, the same hierarchy of nodes as in the first call, but the attributes values are messed up.
I tried making the rapidxml::xml_document<> doc global and also adding the parse_non_destructive flag, none of those make a difference.
If matters, the client using the Load method is running in the same thread. What can be wrong?
std::vector<char> xmlCopy(bytes.begin(), bytes.end());
The local copy of the serial representation of your XML document is local. I would bet that rapidXML makes no copy of the attributes, but rather uses pointers to the sequence. You could check that by looking at the addresses of the attribute values and your document copy.

Passing from a DOMNode* to a DOMElement* in Xerces-C

I have a c++ application that manipulates xml.
Well, at a certain point of my application I get a DOMNode* and then I attach it to an element as a child.
Well the problem is that I would like to add parameters to that node... well it is a node so it is not an element... only elements have parameters...
This is my code:
xercesc::DOMNode* node = 0;
std::string xml = from_an_obj_of_mine.GetXml(); /* A string with xml inside, the xml is sure an element having something inside */
xercesc::MemBufInputSource xml_buf((const XMLByte*)xml.c_str(), xml.size(), "dummy");
xercesc::XercesDOMParser* parser = new xercesc::XercesDOMParser();
parser->parse(xml_buf); /* parser will contain a DOMDocument well parsed from the string, I get here the node i want to attach */
node = my_pointer_to_a_preexisting_domdocument->GetXmlDocument()->importNode(parser->getDocument()->getDocumentElement(), true); /* I want to attach the node in parser to a node of my_pointer_to_an_el_of_my_preexisting_domdocument, it is a different tree, so I must import the node to attach it later */
my_pointer_to_an_el_of_my_preexisting_domdocument->appendChild(node);
As you can see I want to create a node from a string, I create it through a parse and then need to import the node to create a new identical node belonging to the dom tree where I want to attach the new node.
My steps are:
Get the xml string to attach to a pre-existing dom (stored as a domdocument somewhere)
Create a parser
Using the parser create a dom tree from the string
From my pre-existing dom (where I want to attach my new node), call the import and clone the node
so that it can be attached to the pre-existing dom.
Attach it
The problem is that import and import gets me a node... I want an element to attach...
I use appendChild to append elements too... of course the method wants DOMNode* but giving it a DOMElement* (which inherits from DOMNode) is ok...
How can I get an element from a node???
delete wd_parser;
ok I discovered it...
Just re-cast the node to element and it is done... DOMNode is a pure virtual class and it is parent of DOMElement... so it is correct and it is also the way to do things (logically speaking).
DOMElement* = dynamic_cast<DOMElement*>(node);
:)

Add a node to an existing XML document

I am working on a small programm written in C++ using the QT Framework (v. 4.7).
The task I want to accomplish is opening an existing xml-document, add a node within its structure and save the document to the file I read it from before. I have tried this using something like that:
QFile xmlIn(AFileName);
QDomDocument doc("report_1");
if (xmlIn.open(QIODevice::ReadOnly)) {
if (doc.setContent(&xmlIn)) {
QDomElement docElem = doc.documentElement();
QDomNode n = docElem.firstChild();
// Do something with the element here
n = n.nextSibling();
}
}
// Code for saving the edited QDomDocument comes here
But I have the strong feeling that I am overseeing an essential part here, because this seems to be a task that is very common and normally the QT Lib should provide everything one could want :D
Please enlighten me :)
Use a "QXmlStreamWriter"...
QXmlStreamWriter lStreamWriter;
if(lProjectFile.open(QIODevice::WriteOnly|QFile::Text))
{
lStreamWriter.setDevice(&lProjectFile);
lStreamWriter.writeStartDocument();
lStreamWriter.writeStartElement("element");
lStreamWriter.writeAttribute("attribute","value");
lStreamWriter.writeEndElement();
lStreamWriter.writeEndDocument();
lProjectFile.close();
}

getElementsByTagName returns 0-length list when called from didFinishLoad delegate

I'm using the Chromium port of WebKit on Windows and I'm trying to retrieve a list of all of the images in my document. I figured the best way to do this was to implement WebKit::WebFrameClient::didFinishLoading like so:
WebNodeList list = document->getElementsByTagName(L"img");
for (size_t i = 0; i < list.length(); ++i) {
// Manipulate images here...
}
However, when this delegate fires, list.length() returns 0. The only times I've seen it return a list of non-zero length is when I substitute "body" or "head" for "img". Strangely enough, if I call getElementsByTagName(L"img") outside of the delegate, it works correctly.
I'm guessing that the DOM isn't fully loaded when didFinishLoading is called, but that would seem to contradict the delegate's name. Does anyone know what I may be missing here?
It turns out that the mistake was purely on my side. I was caching a pointer to the DOM document in my frame wrapper. Of course, since a frame can outlive a DOM document, I ended up referencing an out-of-date document once I loaded a new page.