how to solve XMLParser.ErrorCode.invalidCharacterError in ios swift? - swift

Question

I have a homework needs to read some rss feeds and build user profile etc.
My problem is when i use XMLParser from foundation, I will encounter "The operation couldn’t be completed. (NSXMLParserErrorDomain error 9.)"
I checked documentation and it seems that I have the invalidCharacterError. I don't think my code have problem since it works well for another url feeds. So what should i do to overcome this problem?
Here is url: http://halley.exp.sis.pitt.edu/comet/utils/_rss.jsp?v=bookmark&user_id=3600
P.S. this feeds contains CDATA so i comment out title and description but it should display date, but it is still show that error. So my concern is that during parsing the xml, it encountered any invalid character and report the error. Anyway to fix it? I have to use this url though.
and some related code are here:
func parseFeed(url: String, completionHandler: (([RSSItem]) -> Void)?)
{
self.parserCompletionHandler = completionHandler
let request = URLRequest(url: URL(string: url)!)
let urlSession = URLSession.shared
let task = urlSession.dataTask(with: request) { (data, response, error) in
guard let data = data else {
if let error = error {
print(error.localizedDescription)
}
return
}
/// parse our xml data
let parser = XMLParser(data: data)
parser.delegate = self
parser.parse()
}
task.resume()
}
// MARK: - XML Parser Delegate
func parser(_ parser: XMLParser, didStartElement elementName: String, namespaceURI: String?, qualifiedName qName: String?, attributes attributeDict: [String : String] = [:])
{
currentElement = elementName
if currentElement == "item" {
currentTitle = ""
currentDescription = ""
currentPubDate = ""
}
}
func parser(_ parser: XMLParser, foundCharacters string: String)
{
switch currentElement {
// case "title": currentTitle += string
// case "description" : currentDescription += string
case "pubDate" : currentPubDate += string
default: break
}
}
func parser(_ parser: XMLParser, didEndElement elementName: String, namespaceURI: String?, qualifiedName qName: String?)
{
if elementName == "item" {
let rssItem = RSSItem(title: currentTitle, description: currentDescription, pubDate: currentPubDate)
self.rssItems.append(rssItem)
}
}
func parserDidEndDocument(_ parser: XMLParser) {
parserCompletionHandler?(rssItems)
}
func parser(_ parser: XMLParser, parseErrorOccurred parseError: Error)
{
print(parseError.localizedDescription)
}

Answer 1

I found an invalid byte 0xFC inside one of the CDATA element in the response of the URL you have shown.
This is invalid as a UTF-8 byte in a document declaring encoding="UTF-8".
You should better tell the server engineer of the URL, that the XML of the RSS feed is invalid.
If you need to work with this sort of ill-formed XML, you need to convert it to the valid UTF-8 data.
0xFC represents ü in ISO-LATIN-1, so you can write something like this.
func parseFeed(url: String, completionHandler: (([RSSItem]) -> Void)?)
{
self.parserCompletionHandler = completionHandler
let request = URLRequest(url: URL(string: url)!)
let urlSession = URLSession.shared
let task = urlSession.dataTask(with: request) { (data, response, error) in
guard var data = data else { //###<-- `var` here
if let error = error {
print(error.localizedDescription)
}
return
}
//### When the input `data` cannot be decoded as a UTF-8 String,
if String(data: data, encoding: .utf8) == nil {
//Interpret the data as an ISO-LATIN-1 String,
let isoLatin1 = String(data: data, encoding: .isoLatin1)!
//And re-encode it as a valid UTF-8
data = isoLatin1.data(using: .utf8)!
}
/// parse our xml data
let parser = XMLParser(data: data)
parser.delegate = self
parser.parse()
}
task.resume()
}
If you need to work other encodings, the problem would be far more difficult, as it is hard to estimate the text encoding properly.
You may need to implement func parser(_ parser: XMLParser, foundCDATA CDATABlock: Data), but that seems to be another issue.