I have a Problem with the SAX parser from LibXML2 in Swift 3.
I want something like XMLPullParser from Android in iOS. Which downloads XML from a server and while downloading it parses the Stream.
My XML looks like this:
<?xml version="1.0" encoding="UTF-8" ?>
<ResultList id="12345678-0" platforms="A;B;C;D;E">
<Book id="1111111111" author="Author A" title="Title A" price="9.95" ... />
<Book id="1111111112" author="Author B" title="Title B" price="2.00" ... />
<Book id="1111111113" author="Author C" title="Title C" price="5.00" ... />
<ResultInfo bookcount="3" />
</ResultList>
So all the data is stored in attributes rather than child nodes.
I've made the following class by myself mostly based by these examples:
XMLPerformance, XMLPerformance-Swift and iOS-XML-Streaming
import Foundation
class LibXMLParser: NSObject, URLSessionDataDelegate {
var url: URL?
var delegate: LibXMLParserDelegate?
var done = false
var context: xmlParserCtxtPtr?
var simpleSAXHandlerStruct: xmlSAXHandler = {
var handler = xmlSAXHandler()
handler.initialized = XML_SAX2_MAGIC
handler.startElementNs = startElementSAX
handler.endElementNs = endElementSAX
handler.characters = charactersFoundSAX
//handler.error = errorEncounteredSAX
return handler
}()
init(url: URL) {
super.init()
self.url = url
}
func parse() {
self.done = false
let session = URLSession(configuration: .default, delegate: self, delegateQueue: OperationQueue.main)
let dataTask = session.dataTask(with: URLRequest(url: url!))
dataTask.resume()
self.context = xmlCreatePushParserCtxt(&simpleSAXHandlerStruct, Unmanaged.passUnretained(self).toOpaque(), nil, 0, nil)
self.delegate?.parserDidStartDocument()
repeat {
RunLoop.current.run(mode: .defaultRunLoopMode, before: Date.distantFuture)
} while !self.done
xmlFreeParserCtxt(self.context)
self.delegate?.parserDidEndDocument()
}
func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {
print("Did receive data")
data.withUnsafeBytes { (bytes: UnsafePointer<CChar>) -> Void in
xmlParseChunk(self.context, bytes, CInt(data.count), 0)
}
}
func urlSessionDidFinishEvents(forBackgroundURLSession session: URLSession) {
xmlParseChunk(self.context, nil, 0, 1)
self.done = true
}
func urlSession(_ session: URLSession, didBecomeInvalidWithError error: Error?) {
self.done = true
//self.delegate?.parserErrorOccurred(error)
}
func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
self.done = true
//self.delegate?.parserErrorOccurred(error)
}
}
private func startElementSAX(_ ctx: UnsafeMutableRawPointer?, name: UnsafePointer<xmlChar>?, prefix: UnsafePointer<xmlChar>?, URI: UnsafePointer<xmlChar>?, nb_namespaces: CInt, namespaces: UnsafeMutablePointer<UnsafePointer<xmlChar>?>?, nb_attributes: CInt, nb_defaulted: CInt, attributes: UnsafeMutablePointer<UnsafePointer<xmlChar>?>?) {
let parser = Unmanaged<LibXMLParser>.fromOpaque(ctx!).takeUnretainedValue()
parser.delegate?.parserDidStartElement(String(cString: name!), nb_attributes: nb_attributes, attributes: attributes)
}
private func endElementSAX(_ ctx: UnsafeMutableRawPointer?, name: UnsafePointer<xmlChar>?,
prefix: UnsafePointer<xmlChar>?,
URI: UnsafePointer<xmlChar>?) {
let parser = Unmanaged<LibXMLParser>.fromOpaque(ctx!).takeUnretainedValue()
parser.delegate?.parserDidEndElement(String(cString: name!))
}
private func charactersFoundSAX(_ ctx: UnsafeMutableRawPointer?, ch: UnsafePointer<xmlChar>?, len: CInt) {
let parser = Unmanaged<LibXMLParser>.fromOpaque(ctx!).takeUnretainedValue()
parser.delegate?.parserFoundCharacters(String(cString: ch!))
}
I initialize this class with an URL. When i call parse() it creates a URLSession and a URLSessionDataTask with an delegate to self to override the method didReceive data: Data.
After that i create a xmlParserCtxtPtr and loop until the dataTask is finished.
When it receives data I parse it with the xmlParseChunk method and startElementSAX calls the delegate that I've set from a ViewController class. (I just need the element name, number of attributes and attributes.)
So far so good.
In my ViewController (UITableViewController) I have the following code:
func downloadBooksLibXML() {
print("Downloading…")
UIApplication.shared.isNetworkActivityIndicatorVisible = true
DispatchQueue.global().async {
print("Setting up parser")
let parser = LibXMLParser(url: URL(string: self.baseUrl + self.parameters!)!)
parser.delegate = self
parser.parse()
}
}
func parserDidStartDocument() {
}
func parserDidEndDocument() {
DispatchQueue.main.sync {
UIApplication.shared.isNetworkActivityIndicatorVisible = false
self.isDone = true
print("Finished")
}
}
func parserDidStartElement(_ elementName: String, nb_attributes: CInt, attributes: UnsafeMutablePointer<UnsafePointer<xmlChar>?>?) {
print(elementName)
switch elementName {
case "Book":
DispatchQueue.main.async {
let book = self.buildBook(nb_attributes: nb_attributes, attributes: attributes)
self.books.append(book)
self.tableView.beginUpdates()
self.tableView.insertRows(at: [IndexPath(row: self.books.count - 1, section: 0)], with: .automatic)
self.tableView.endUpdates()
self.navigationItem.title = String(format: NSLocalizedString("books_found", comment: "Books found"), "\(self.books.count)")
}
case "ResultList":
break
case "ResultInfo":
break
default:
break
}
}
func buildBook(nb_attributes: CInt, attributes: UnsafeMutablePointer<UnsafePointer<xmlChar>?>?) -> Book {
let fields = 5 /* (localname/prefix/URI/value/end) */
let book = Book()
for i in 0..<Int(nb_attributes) {
if let localname = attributes?[i * fields + 0],
//let prefix = attributes?[i * fields + 1],
//let URI = attributes?[i * fields + 2],
let value_start = attributes?[i * fields + 3],
let value_end = attributes?[i * fields + 4] {
let localnameString = String(cString: localname)
let string_start = String(cString: value_start)
let string_end = String(cString: value_end)
let diff = string_start.characters.count - string_end.characters.count
if diff > 0 {
let value = string_start.substring(to: string_start.index(string_start.startIndex, offsetBy: diff))
book.setValue(value, forKey: localnameString)
}
}
}
return book
}
func parserDidEndElement(_ elementName: String) {
}
func parserFoundCharacters(_ string: String) {
}
func parserErrorOccurred(_ parseError: Error?) {
}
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Update
So the problem getting the attribute values has been fixed by the answer from nwellnhof. I've updated my code above to a much better code. It doesn't iterate through all the attributes now anymore. Now my new problem:
I've created the method buildBook to get a Book object of the XML attributes.
I've mostly translated the method from here What is the right way to get attribute value in libXML sax parser (C++)? to Swift and used setValue(value: Any?, forKey: String) to set the attributes of my book object.
But now my problem is that it doesn't update the tableView.
I've tried executing the buildBook method synchronous in a background thread using DispatchQueue.global().sync and the tableView update in an asynchronous main thread using DispatchQueue.main.async. But then it crashes at tableView.endUpdates() although it's in the main thread.
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Any help would be highly appreciated.
Seems like a simple off-by-one error. To iterate the attributes array in C, I'd write something like:
But you're using the closed range operator which includes the upper bound:
So you should use the half-open range operator instead:
By the way, libxml2 also has a pull parser interface modeled after C#'s
XmlTextReaderwhich is much easier to use than the SAX parser.