etree
The etree package is a lightweight, pure go package that expresses XML in the form of an element tree. Its design was inspired by the Python ElementTree module.
Some of the package's capabilities and features:
- Represents XML documents as trees of elements for easy traversal.
- Imports, serializes, modifies or creates XML documents from scratch.
- Writes and reads XML to/from files, byte slices, strings and io interfaces.
- Performs simple or complex searches with lightweight XPath-like query APIs.
- Auto-indents XML using spaces or tabs for better readability.
- Implemented in pure go; depends only on standard go libraries.
- Built on top of the go encoding/xml package.
Creating an XML document
The following example creates an XML document from scratch using the etree package and outputs its indented contents to stdout.
doc := etree.NewDocument()
doc.CreateProcInst("xml", `version="1.0" encoding="UTF-8"`)
doc.CreateProcInst("xml-stylesheet", `type="text/xsl" href="style.xsl"`)
people := doc.CreateElement("People")
people.CreateComment("These are all known people")
jon := people.CreateElement("Person")
jon.CreateAttr("name", "Jon")
sally := people.CreateElement("Person")
sally.CreateAttr("name", "Sally")
doc.Indent(2)
doc.WriteTo(os.Stdout)
Output:
<?xml version="1.0" encoding="UTF-8"?>
<?xml-stylesheet type="text/xsl" href="style.xsl"?>
<People>
<!--These are all known people-->
<Person name="Jon"/>
<Person name="Sally"/>
</People>
Reading an XML file
Suppose you have a file on disk called bookstore.xml containing the following data:
<bookstore xmlns:p="urn:schemas-books-com:prices">
<book category="COOKING">
<title lang="en">Everyday Italian</title>
<author>Giada De Laurentiis</author>
<year>2005</year>
<p:price>30.00</p:price>
</book>
<book category="CHILDREN">
<title lang="en">Harry Potter</title>
<author>J K. Rowling</author>
<year>2005</year>
<p:price>29.99</p:price>
</book>
<book category="WEB">
<title lang="en">XQuery Kick Start</title>
<author>James McGovern</author>
<author>Per Bothner</author>
<author>Kurt Cagle</author>
<author>James Linn</author>
<author>Vaidyanathan Nagarajan</author>
<year>2003</year>
<p:price>49.99</p:price>
</book>
<book category="WEB">
<title lang="en">Learning XML</title>
<author>Erik T. Ray</author>
<year>2003</year>
<p:price>39.95</p:price>
</book>
</bookstore>
This code reads the file's contents into an etree document.
doc := etree.NewDocument()
if err := doc.ReadFromFile("bookstore.xml"); err != nil {
panic(err)
}
You can also read XML from a string, a byte slice, or an io.Reader.
Processing elements and attributes
This example illustrates several ways to access elements and attributes using etree selection queries.
root := doc.SelectElement("bookstore")
fmt.Println("ROOT element:", root.Tag)
for _, book := range root.SelectElements("book") {
fmt.Println("CHILD element:", book.Tag)
if title := book.SelectElement("title"); title != nil {
lang := title.SelectAttrValue("lang", "unknown")
fmt.Printf(" TITLE: %s (%s)\n", title.Text(), lang)
}
for _, attr := range book.Attr {
fmt.Printf(" ATTR: %s=%s\n", attr.Key, attr.Value)
}
}
Output:
ROOT element: bookstore
CHILD element: book
TITLE: Everyday Italian (en)
ATTR: category=COOKING
CHILD element: book
TITLE: Harry Potter (en)
ATTR: category=CHILDREN
CHILD element: book
TITLE: XQuery Kick Start (en)
ATTR: category=WEB
CHILD element: book
TITLE: Learning XML (en)
ATTR: category=WEB
Path queries
This example uses etree's path functions to select all book titles that fall into the category of 'WEB'. The double-slash prefix in the path causes the search for book elements to occur recursively; book elements may appear at any level of the XML hierarchy.
for _, t := range doc.FindElements("//book[@category='WEB']/title") {
fmt.Println("Title:", t.Text())
}
Output:
Title: XQuery Kick Start
Title: Learning XML
This example finds the first book element under the root bookstore element and outputs the tag and text of each of its child elements.
for _, e := range doc.FindElements("./bookstore/book[1]/*") {
fmt.Printf("%s: %s\n", e.Tag, e.Text())
}
Output:
title: Everyday Italian
author: Giada De Laurentiis
year: 2005
price: 30.00
This example finds all books with a price of 49.99 and outputs their titles.
path := etree.MustCompilePath("./bookstore/book[p:price='49.99']/title")
for _, e := range doc.FindElementsPath(path) {
fmt.Println(e.Text())
}
Output:
XQuery Kick Start
Note that this example uses the FindElementsPath function, which takes as an argument a pre-compiled path object. Use precompiled paths when you plan to search with the same path more than once.
Other features
These are just a few examples of the things the etree package can do. See the documentation for a complete description of its capabilities.
Contributing
This project accepts contributions. Just fork the repo and submit a pull request!
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