View Source XML Builder

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Overview

An Elixir library for building XML. It is inspired by the late Jim Weirich's awesome builder library for Ruby.

Each XML node is structured as a tuple of name, attributes map, and content/list.

{name, attrs, content | list}

Installation

Add dependency to your project's mix.exs:

def deps do
  [{:xml_builder, "~> 2.1"}]
end

Examples

A simple element

Like <person id="12345">Josh</person>, would look like:

{:person, %{id: 12345}, "Josh"} |> XmlBuilder.generate

An element with child elements

Like <person id="12345"><first>Josh</first><last>Nussbaum</last></person>.

{:person, %{id: 12345}, [{:first, nil, "Josh"}, {:last, nil, "Nussbaum"}]} |> XmlBuilder.generate

Convenience Functions

For more readability, you can use XmlBuilder's methods instead of creating tuples manually.

XmlBuilder.document(:person, "Josh") |> XmlBuilder.generate

Outputs:

<?xml version="1.0" encoding="UTF-8" ?>
<person>Josh</person>

Building up an element

An element can be built using multiple calls to the element function.

import XmlBuilder

def person(id, first, last) do
  element(:person, %{id: id}, [
    element(:first, first),
    element(:last, last)
  ])
end

iex> [person(123, "Steve", "Jobs"),
      person(456, "Steve", "Wozniak")] |> generate

Outputs.

<person id="123">
  <first>Steve</first>
  <last>Jobs</last>
</person>
<person id="456">
  <first>Steve</first>
  <last>Wozniak</last>
</person>

Using keyed lists

The previous example can be simplified using a keyed list.

import XmlBuilder

def person(id, first, last) do
  element(:person, %{id: id}, first: first,
                              last: last)
end

iex> person(123, "Josh", "Nussbaum") |> generate(format: :none)
"<person id=\"123\"><first>Josh</first><last>Nussbaum</last></person>"

Namespaces

To use a namespace, add an xmlns attribute to the root element.

To use multiple schemas, specify a xmlns:nsName attribute for each schema and use a colon : in the element name, ie nsName:elementName.

import XmlBuilder

iex> generate({:example, [xmlns: "http://schemas.example.tld/1999"], "content"})
"<example xmlns=\"http://schemas.example.tld/1999\">content</example>"

iex> generate({:"nsName:elementName", ["xmlns:nsName": "http://schemas.example.tld/1999"], "content"})
"<nsName:elementName xmlns:nsName=\"http://schemas.example.tld/1999\">content</nsName:elementName>"

DOCTYPE declarations

A DOCTYPE can be declared by applying the doctype function at the first position of a list of elements in a document definition:

import XmlBuilder

document([
  doctype("html", public: ["-//W3C//DTD XHTML 1.0 Transitional//EN",
                "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"]),
  element(:html, "Hello, world!")
]) |> generate

Outputs.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html>Hello, world!</html>

Encoding

While the output is always UTF-8 and has to be converted in another place, you can override the encoding statement in the XML declaration with the encoding option.

import XmlBuilder

document(:oldschool)
|> generate(encoding: "ISO-8859-1")
|> :unicode.characters_to_binary(:unicode, :latin1)

Outputs.

<?xml version="1.0" encoding="ISO-8859-1"?>
<oldschool/>

Using iodata() directly

While by default, output from generate/2 is converted to binary(), you can use generate_iodata/2 to skip this conversion. This can be convenient if you're using IO.binwrite/2 on a :raw IO device, as these APIs can work with iodata() directly, leading to some performance gains.

In some scenarios, it may be beneficial to generate part of your XML upfront, for instance when generating a sitemap.xml, you may have shared fields for author. Instead of generating this each time, you could do the following:

import XmlBuilder

entries = [%{title: "Test", url: "https://example.org/"}]

# Generate static author data upfront
author = generate_iodata(element(:author, [
  element(:name, "John Doe"),
  element(:uri, "https://example.org/")
]))

file = File.open!("path/to/file", [:raw])

for entry <- entries do
  iodata =
    generate_iodata(element(:entry, [
      # Reuse the static pre-generated fields as-is
      {:iodata, author},

      # Dynamic elements are generated for each entry
      element(:title, entry.title),
      element(:link, entry.url)
    ]))

  IO.binwrite(file, iodata)
end

Escaping

XmlBuilder offers 3 distinct ways to control how content of tags is escaped and handled:

  • By default, any content is escaped, replacing reserved characters (& " ' < >) with their equivalent entity (&amp; etc.)
  • If content is wrapped in {:cdata, cdata}, the content in cdata is wrapped with <![CDATA[...]]>, and not escaped. You should make sure the content itself does not contain ]]>.
  • If content is wrapped in {:safe, data}, the content in data is not escaped, but will be stringified if not a bitstring. Use this option carefully. It may be useful when data is guaranteed to be safe (numeric data).
  • If content is wrapped in {:iodata, data}, either in the top level or within a list, the data is used as iodata(), and will not be escaped, indented or stringified. An example of this can be seen in the "Using iodata() directly" example above.

Standalone

Should you need standalone="yes" in the XML declaration, you can pass standalone: true as option to the generate/2 call.

import XmlBuilder

document(:outsider)
|> generate(standalone: true)

Outputs.

<?xml version="1.0" standalone="yes"?>
<outsider/>

If otherwise you need standalone ="no" in the XML declaration, you can pass standalone: false as an option to thegenerate / 2 call.

Outputs.

<?xml version="1.0" standalone="no"?>
<outsider/>

Formatting

To remove indentation, pass format: :none option to XmlBuilder.generate/2.

doc |> XmlBuilder.generate(format: :none)

The default is to formatting with indentation, which is equivalent to XmlBuilder.generate(doc, format: :indent).

License

This source code is licensed under the MIT License. Copyright (c) 2014-present, Joshua Nussbaum. All rights reserved.