XML.jl

Read and write XML in pure Julia.

Introduction

This package offers fast data structures for reading and writing XML files with a consistent interface:

Node/LazyNode Interface:

nodetype(node)      →   XML.NodeType (an enum type)
tag(node)           →   String or Nothing
attributes(node)    →   OrderedDict{String, String} or Nothing
value(node)         →   String or Nothing
children(node)      →   Vector{typeof(node)}
is_simple(node)     →   Bool (whether node is simple .e.g. <tag>item</tag>)
simple_value(node)   →   e.g. "item" from <tag>item</tag>)

Extended Interface for LazyNode

depth(node)         →   Int
next(node)          →   typeof(node)
prev(node)          →   typeof(node)
parent(node)        →   typeof(node)

Quickstart

using XML

filename = joinpath(dirname(pathof(XML)), "..", "test", "data", "books.xml")

doc = read(filename, Node)

children(doc)
# 2-Element Vector{Node}:
#  Node Declaration <?xml version="1.0"?>
#  Node Element <catalog> (12 children)

doc[end]  # The root node
# Node Element <catalog> (12 children)

doc[end][2]  # Second child of root
# Node Element <book id="bk102"> (6 children)

Data Structures that Represent XML Nodes

Preliminary: NodeType

• Each item in an XML DOM is classified by its NodeType.
• Every XML.jl struct defines a nodetype(x) method that returns its NodeType.

NodeType	XML Representation	Node Constructor
Document	An entire document	Document(children...)
DTD	<!DOCTYPE ...>	DTD(...)
Declaration	<?xml attributes... ?>	Declaration(; attrs...)
ProcessingInstruction	<?tag attributes... ?>	ProcessingInstruction(tag; attrs...)
Comment	<!-- text -->	Comment(text)
CData	<![CData[text]]>	CData(text)
Element	<tag attributes... > children... </NAME>	Element(tag, children...; attrs...)
Text	the text part of <tag>text</tag>	Text(text)

Node: Probably What You're Looking For

• read-ing a Node loads the entire XML DOM in memory.
• See the table above for convenience constructors.
• Nodes have some additional methods that aid in construction/mutation:

# Add a child:
push!(parent::Node, child::Node)

# Replace a child:
parent[2] = child

# Add/change an attribute:
node["key"] = value

node["key"]

• Node is an immutable type. However, you can easily create a copy with one or more field values changed by using the Node(::Node; kw...) constructor where kw are the fields you want to change. For example:

node = XML.Element("tag", XML.Text("child"))

simple_value(node)
# "child"

node2 = Node(node, children=XML.Text("changed"))

simple_value(node2)
# "changed"

Writing Element Nodes with XML.h

Similar to Cobweb.jl, XML.h enables you to write elements with a simpler syntax:

using XML: h

julia> node = h.parent(
         h.child("first child content", id="id1"),
         h.child("second child content", id="id2")
       )
# Node Element <parent> (2 children)

julia> print(XML.write(node))
# <parent>
#   <child id="id1">first child content</child>
#   <child id="id2">second child content</child>
# </parent>

XML.LazyNode: For Fast Iteration through an XML File

A lazy data structure that just keeps track of the position in the raw data (Vector{UInt8}) to read from.

• You can iterate over a LazyNode to "read" through an XML file:

doc = read(filename, LazyNode)

foreach(println, doc)
# LazyNode Declaration <?xml version="1.0"?>
# LazyNode Element <catalog>
# LazyNode Element <book id="bk101">
# LazyNode Element <author>
# LazyNode Text "Gambardella, Matthew"
# LazyNode Element <title>
# ⋮

Reading

# Reading from file:
read(filename, Node)
read(filename, LazyNode)

# Parsing from string:
parse(Node, str)
parse(LazyNode, str)

Writing

XML.write(filename::String, node)  # write to file

XML.write(io::IO, node)  # write to stream

XML.write(node)  # String

Performance

• XML.jl performs comparatively to EzXML.jl, which wraps the C library libxml2.
• See the benchmarks/suite.jl for the code to produce these results.
• The following output was generated in a Julia session with the following versioninfo:

julia> versioninfo()
Julia Version 1.9.4
Commit 8e5136fa297 (2023-11-14 08:46 UTC)
Build Info:
  Official https://julialang.org/ release
Platform Info:
  OS: macOS (arm64-apple-darwin22.4.0)
  CPU: 10 × Apple M1 Pro
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-14.0.6 (ORCJIT, apple-m1)
  Threads: 8 on 8 virtual cores

Reading an XML File

       XML.LazyNode   0.009583
           XML.Node  ■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■ 1071.32
      EzXML.readxml  ■■■■■■■■■ 284.346
   XMLDict.xml_dict  ■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■ 1231.47

Writing an XML File

         Write: XML  ■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■ 289.638
       Write: EzXML  ■■■■■■■■■■■■■ 93.4631

Lazily Iterating over Each Node

           LazyNode  ■■■■■■■■■ 51.752
 EzXML.StreamReader  ■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■ 226.271

Collecting All Names/Tags in an XML File

       XML.LazyNode  ■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■ 210.482
 EzXML.StreamReader  ■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■ 276.238
      EzXML.readxml  ■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■ 263.269

Possible Gotchas

• XML.jl doesn't automatically escape special characters (<, >, &, ", and ' ) for you. However, we provide utility functions for doing the conversions back and forth:
  • XML.escape(::String) and XML.unescape(::String)
  • XML.escape!(::Node) and XML.unescape!(::Node).