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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 features include:

  • 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!