sample.xml

<?xml version="1.0"?>
<catalog>
    <book id="bk101">
        <author>Gambardella, Matthew</author>
        <title>XML Developer's Guide</title>
        <genre>Computer</genre>
        <price>44.95</price>
        <publish_date>2000-10-01</publish_date>
        <description>An in-depth look at creating applications
            with XML.</description>
    </book>
    <book id="bk102">
        <author>Ralls, Kim</author>
        <title>Midnight Rain</title>
        <genre>Fantasy</genre>
        <price>5.95</price>
        <publish_date>2000-12-16</publish_date>
        <description>A former architect battles corporate zombies,
            an evil sorceress, and her own childhood to become queen
            of the world.</description>
    </book>
    <book id="bk103">
        <author>Corets, Eva</author>
        <title>Maeve Ascendant</title>
        <genre>Fantasy</genre>
        <price>5.95</price>
        <publish_date>2000-11-17</publish_date>
        <description>After the collapse of a nanotechnology
            society in England, the young survivors lay the
            foundation for a new society.</description>
    </book>
    <book id="bk104">
        <author>Corets, Eva</author>
        <title>Oberon's Legacy</title>
        <genre>Fantasy</genre>
        <price>5.95</price>
        <publish_date>2001-03-10</publish_date>
        <description>In post-apocalypse England, the mysterious
            agent known only as Oberon helps to create a new life
            for the inhabitants of London. Sequel to Maeve
            Ascendant.</description>
    </book>
    <book id="bk105">
        <author>Corets, Eva</author>
        <title>The Sundered Grail</title>
        <genre>Fantasy</genre>
        <price>5.95</price>
        <publish_date>2001-09-10</publish_date>
        <description>The two daughters of Maeve, half-sisters,
            battle one another for control of England. Sequel to
            Oberon's Legacy.</description>
    </book>
    <book id="bk106">
        <author>Randall, Cynthia</author>
        <title>Lover Birds</title>
        <genre>Romance</genre>
        <price>4.95</price>
        <publish_date>2000-09-02</publish_date>
        <description>When Carla meets Paul at an ornithology
            conference, tempers fly as feathers get ruffled.</description>
    </book>
    <book id="bk107">
        <author>Thurman, Paula</author>
        <title>Splish Splash</title>
        <genre>Romance</genre>
        <price>4.95</price>
        <publish_date>2000-11-02</publish_date>
        <description>A deep sea diver finds true love twenty
            thousand leagues beneath the sea.</description>
    </book>
    <book id="bk108">
        <author>Knorr, Stefan</author>
        <title>Creepy Crawlies</title>
        <genre>Horror</genre>
        <price>4.95</price>
        <publish_date>2000-12-06</publish_date>
        <description>An anthology of horror stories about roaches,
            centipedes, scorpions  and other insects.</description>
    </book>
    <book id="bk109">
        <author>Kress, Peter</author>
        <title>Paradox Lost</title>
        <genre>Science Fiction</genre>
        <price>6.95</price>
        <publish_date>2000-11-02</publish_date>
        <description>After an inadvertant trip through a Heisenberg
            Uncertainty Device, James Salway discovers the problems
            of being quantum.</description>
    </book>
    <book id="bk110">
        <author>O'Brien, Tim</author>
        <title>Microsoft .NET: The Programming Bible</title>
        <genre>Computer</genre>
        <price>36.95</price>
        <publish_date>2000-12-09</publish_date>
        <description>Microsoft's .NET initiative is explored in
            detail in this deep programmer's reference.</description>
    </book>
    <book id="bk111">
        <author>O'Brien, Tim</author>
        <title>MSXML3: A Comprehensive Guide</title>
        <genre>Computer</genre>
        <price>36.95</price>
        <publish_date>2000-12-01</publish_date>
        <description>The Microsoft MSXML3 parser is covered in
            detail, with attention to XML DOM interfaces, XSLT processing,
            SAX and more.</description>
    </book>
    <book id="bk112">
        <author>Galos, Mike</author>
        <title>Visual Studio 7: A Comprehensive Guide</title>
        <genre>Computer</genre>
        <price>49.95</price>
        <publish_date>2001-04-16</publish_date>
        <description>Microsoft Visual Studio 7 is explored in depth,
            looking at how Visual Basic, Visual C++, C#, and ASP+ are 
            integrated into a comprehensive development 
            environment.</description>
    </book>
</catalog>

sampleoutput.txt

Key: catalog 
Value: [ ] 

    
Key: book 
Value: [ ] 
Attributes: [id: bk101]

        
Key: author 
Value: [Gambardella, Matthew] 

        
Key: title 
Value: [XML Developer's Guide] 

        
Key: genre 
Value: [Computer] 

        
Key: price 
Value: [44.95] 

        
Key: publish_date 
Value: [2000-10-01] 

        
Key: description 
Value: [An in-depth look at creating applications with XML.] 

    
Key: book 
Value: [ ] 
Attributes: [id: bk102]

        
Key: author 
Value: [Ralls, Kim] 

        
Key: title 
Value: [Midnight Rain] 

        
Key: genre 
Value: [Fantasy] 

        
Key: price 
Value: [5.95] 

        
Key: publish_date 
Value: [2000-12-16] 

        
Key: description 
Value: [A former architect battles corporate zombies, an evil sorceress, and her own childhood to become queen of the world.] 

    
Key: book 
Value: [ ] 
Attributes: [id: bk103]

        
Key: author 
Value: [Corets, Eva] 

        
Key: title 
Value: [Maeve Ascendant] 

        
Key: genre 
Value: [Fantasy] 

        
Key: price 
Value: [5.95] 

        
Key: publish_date 
Value: [2000-11-17] 

        
Key: description 
Value: [After the collapse of a nanotechnology society in England, the young survivors lay the foundation for a new society.] 

    
Key: book 
Value: [ ] 
Attributes: [id: bk104]

        
Key: author 
Value: [Corets, Eva] 

        
Key: title 
Value: [Oberon's Legacy] 

        
Key: genre 
Value: [Fantasy] 

        
Key: price 
Value: [5.95] 

        
Key: publish_date 
Value: [2001-03-10] 

        
Key: description 
Value: [In post-apocalypse England, the mysterious agent known only as Oberon helps to create a new life for the inhabitants of London. Sequel to Maeve Ascendant.] 

    
Key: book 
Value: [ ] 
Attributes: [id: bk105]

        
Key: author 
Value: [Corets, Eva] 

        
Key: title 
Value: [The Sundered Grail] 

        
Key: genre 
Value: [Fantasy] 

        
Key: price 
Value: [5.95] 

        
Key: publish_date 
Value: [2001-09-10] 

        
Key: description 
Value: [The two daughters of Maeve, half-sisters, battle one another for control of England. Sequel to Oberon's Legacy.] 

    
Key: book 
Value: [ ] 
Attributes: [id: bk106]

        
Key: author 
Value: [Randall, Cynthia] 

        
Key: title 
Value: [Lover Birds] 

        
Key: genre 
Value: [Romance] 

        
Key: price 
Value: [4.95] 

        
Key: publish_date 
Value: [2000-09-02] 

        
Key: description 
Value: [When Carla meets Paul at an ornithology conference, tempers fly as feathers get ruffled.] 

    
Key: book 
Value: [ ] 
Attributes: [id: bk107]

        
Key: author 
Value: [Thurman, Paula] 

        
Key: title 
Value: [Splish Splash] 

        
Key: genre 
Value: [Romance] 

        
Key: price 
Value: [4.95] 

        
Key: publish_date 
Value: [2000-11-02] 

        
Key: description 
Value: [A deep sea diver finds true love twenty thousand leagues beneath the sea.] 

    
Key: book 
Value: [ ] 
Attributes: [id: bk108]

        
Key: author 
Value: [Knorr, Stefan] 

        
Key: title 
Value: [Creepy Crawlies] 

        
Key: genre 
Value: [Horror] 

        
Key: price 
Value: [4.95] 

        
Key: publish_date 
Value: [2000-12-06] 

        
Key: description 
Value: [An anthology of horror stories about roaches, centipedes, scorpions and other insects.] 

    
Key: book 
Value: [ ] 
Attributes: [id: bk109]

        
Key: author 
Value: [Kress, Peter] 

        
Key: title 
Value: [Paradox Lost] 

        
Key: genre 
Value: [Science Fiction] 

        
Key: price 
Value: [6.95] 

        
Key: publish_date 
Value: [2000-11-02] 

        
Key: description 
Value: [After an inadvertant trip through a Heisenberg Uncertainty Device, James Salway discovers the problems of being quantum.] 

    
Key: book 
Value: [ ] 
Attributes: [id: bk110]

        
Key: author 
Value: [O'Brien, Tim] 

        
Key: title 
Value: [Microsoft .NET: The Programming Bible] 

        
Key: genre 
Value: [Computer] 

        
Key: price 
Value: [36.95] 

        
Key: publish_date 
Value: [2000-12-09] 

        
Key: description 
Value: [Microsoft's .NET initiative is explored in detail in this deep programmer's reference.] 

    
Key: book 
Value: [ ] 
Attributes: [id: bk111]

        
Key: author 
Value: [O'Brien, Tim] 

        
Key: title 
Value: [MSXML3: A Comprehensive Guide] 

        
Key: genre 
Value: [Computer] 

        
Key: price 
Value: [36.95] 

        
Key: publish_date 
Value: [2000-12-01] 

        
Key: description 
Value: [The Microsoft MSXML3 parser is covered in detail, with attention to XML DOM interfaces, XSLT processing, SAX and more.] 

    
Key: book 
Value: [ ] 
Attributes: [id: bk112]

        
Key: author 
Value: [Galos, Mike] 

        
Key: title 
Value: [Visual Studio 7: A Comprehensive Guide] 

        
Key: genre 
Value: [Computer] 

        
Key: price 
Value: [49.95] 

        
Key: publish_date 
Value: [2001-04-16] 

        
Key: description 
Value: [Microsoft Visual Studio 7 is explored in depth, looking at how Visual Basic, Visual C++, C#, and ASP+ are integrated into a comprehensive development environment.] 

xmlstuff.swift

import Foundation

public struct Node: CustomStringConvertible {
    public var children: [Node] = []
    public var key = ""
    public var leafValue: String?  = nil
    public var cleanLeafValue: String? {
        if var leafValue = leafValue {
            leafValue = (leafValue as NSString).replacingOccurrences(of: "\n", with: "")
            leafValue = (leafValue as NSString).replacingOccurrences(of: "\\s+", with: " ", options: [.regularExpression], range: NSMakeRange(0, leafValue.characters.count))
            if !leafValue.isEmpty {return leafValue}
        }
        return nil
    }
    public var attributes: [NSObject: AnyObject]? = nil
    public var description: String {return "Key: \(key) Value: \(leafValue) Attributes: \(attributes) Children: \(children)"}
}

public extension Node {
    public func showNode(_ indent: Int = 0) {
        let indentation = String(repeating: " ", count: indent)
        Swift.print(indentation)
        Swift.print("Key: \(key) ")
        if let leafValue = cleanLeafValue {Swift.print("Value: [\(leafValue)] ")}
        if let attributes = attributes {
            if !(attributes.keys).isEmpty {
                print("Attributes: ", terminator: "")
                debugPrint(attributes)
            }
        }
        Swift.print("")
        for child in children {child.showNode(indent + 4)}
    }
}

public extension Node {
    public var keys: [String] {return children.map({$0.key})}
    public func childrenWithKey(_ keyString: String) -> [Node]{
        return children.filter({$0.key == keyString})
    }
    public func childWithKey(_ keyString: String) -> Node? {
        return childrenWithKey(keyString).first
    }
}

public final class MyXMLParser: NSObject, XMLParserDelegate {
    var stack: [Node] = []
    
    public static func parse(xmlString: String) -> Node? {
        let instance = MyXMLParser()
        return instance.parseXMLString(xmlString)
    }
    
    public static func parse(xmlData: Data) -> Node? {
        let instance = MyXMLParser()
        return instance.parseXMLData(xmlData)
    }
    
    public func parseXMLData(_ xmlData: Data) -> Node? {
        stack.append(Node())
        let parser = Foundation.XMLParser(data: xmlData)
        parser.shouldResolveExternalEntities = true
        parser.delegate = self
        parser.parse()
        let parent = stack.last
        return parent?.children.last
    }
    
    public func parseXMLString(_ xml: String) -> Node? {
        if let data = xml.data(using: String.Encoding.utf8, allowLossyConversion: false) {
            return parseXMLData(data)
        }
        return nil
    }

    public func parser(
        _ parser: XMLParser,
        didStartElement elementName: String,
        namespaceURI: String?,
        qualifiedName qName: String?,
        attributes attributeDict: [String : String] = [:])
    {
        var node = Node()
        node.key = elementName
        node.attributes = attributeDict as [NSObject : AnyObject]?
        stack.append(node)
    }
    
    public func parser(
        _ parser: XMLParser,
        didEndElement elementName: String,
        namespaceURI: String?,
        qualifiedName qName: String?)
    {
        
        let node = stack.removeLast()
        var parent = stack.removeLast()
        parent.children.append(node)
        stack.append(parent)
    }
    
    public func parser(_ parser: XMLParser, foundCharacters string: String) {
        if !stack.isEmpty {
            var node = stack.removeLast()
            if let leafValue = node.leafValue {
                node.leafValue = leafValue + string
            } else {
                node.leafValue = string
            }
            stack.append(node)
        }
    }
}