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# Copyright 2008 Amazon.com, Inc. or its affiliates. All Rights
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# Reserved. Licensed under the Amazon Software License (the
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# "License"). You may not use this file except in compliance with the
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# License. A copy of the License is located at
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# http://aws.amazon.com/asl or in the "license" file accompanying this
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# file. This file is distributed on an "AS IS" BASIS, WITHOUT
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# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
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# the License for the specific language governing permissions and
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# limitations under the License.
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# This class makes it easy to build up xml docs, xpath style.
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# # Create an XMLBuilder:
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# doc = REXML::Document.new(some_xml)
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# builder = XMLBuilder.new(doc)
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# # Add some text elements
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# builder[/book/title] = 'Atlas Shrugged'
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# builder[/book/author] = 'Ann Raynd'
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# builder[/book/author@salutation] = 'Mrs.'
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# Results in the following xml:
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# <title>Atlas Shrugged</title>
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# <author salutation="Mrs.">Ann Raynd</author>
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# - If the path starts with a '/' the path is absolute.
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# - If the path does not start with a '/' the path is relative.
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# - When adding an element the return value is an xml builder object anchored at that path
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# - When adding an attrubte the return value is ... ??? dunno what is should be. nil?
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# - To set the element value use XMLBuilder[]=(string) or XMLBuilder[]=(XMLBuilder) or XMLBuilder[]=(node)
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# - To add an element do builder[path] << string or builder[path] << element or builder[path] << node
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# - If you assign a nil value the value will not be set and the path elements not created.
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require 'rexml/document'
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# Create a new XMLBuilder rooted at the given element, or at a new document if no root is given
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def initialize(root = nil)
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@root = root || REXML::Document.new()
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# Retrieve a builder for the element at the given path
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nodes = PathParser.parse(path)
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rexml_node = nodes.inject(@root) do |rexml_node, parser_node|
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parser_node.walk_visit(rexml_node)
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XMLBuilder.new(nodes.last.retrieve_visit(rexml_node))
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# Set the value of the element or attribute at the given path
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# Don't create elements or make assignments for nil values
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nodes = PathParser.parse(path)
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rexml_node = nodes.inject(@root) do |rexml_node, parser_node|
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parser_node.walk_visit(rexml_node)
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nodes.last.assign_visit(rexml_node, value)
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# Parses an xpath like expression
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def PathParser.parse(path)
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nodes = path.split('/')
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while (nodes.length > 0)
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node = Node.new(first, nodes)
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@nodes << Document.new() if node.document
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@nodes << Element.new(node.element, node.index) if node.element
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@nodes << Attribute.new(node.attribute) if node.attribute
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# Helper class used by PathParser
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attr_reader :attribute
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# Regex for parsing path if the form element[index]@attribute
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# where [index] and @attribute are optional
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@@attribute_regex = /^@(\w+)$/
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@@node_regex = /^(\w+)(?:\[(\d+)\])?(?:@(\w+))?$/
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# Nodes is path.split('/')
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def initialize(allow_document, nodes)
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if allow_document && nodes[0] == ''
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nodes.shift while nodes[0] == ''
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if (match = @@node_regex.match(node))
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@index = match[2].to_i || 0
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elsif (match = @@attribute_regex.match(node))
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@attribute = match[1]
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raise 'Invalid path: Node must be of the form element[index] or @attribute' if document
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# Each class represents a node type. An array of these classes is built up when
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# the path is parsed. Each node is then visited by the current rexml node and
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# (depending on which visit function is called) the action taken.
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# The visit function are:
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# - walk: Walks down the xml dom
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# - assign: Assigns the value to rexml node
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# - retrieve: Retrives the value of the rexml node
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# Different node types implement different behaviour types. For example retrieve is
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# illegal on Attribute nodes, but on Document and Attribute nodes the given node is returned.
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# Move to the document node (top of the xml dom)
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def walk_visit(rexml_node)
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return rexml_node if rexml_node.is_a?(REXML::Document)
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raise "No document set on node. #{rexml_node.name}" if rexml_node.document == nil
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def assign_visit(document_node, value)
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raise 'Can only assign REXML::Elements to document nodes' if !value.is_a?(REXML::Element)
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raise 'Expected a document node' if !document_node.is_a?(REXML::Element)
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doc.replace_child(doc.root, value)
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doc.add_element(element)
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def retrieve_visit(document_node)
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def initialize(name, index)
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# Move one element down in the dom
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def walk_visit(rexml_node)
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elements = rexml_node.get_elements(name)
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raise "Invalid index #{index} for element #{@name}" if @index > elements.length
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# Create a node if it doesn't exist
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if @index == elements.length
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new_element = REXML::Element.new(@name)
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rexml_node.add_element(new_element)
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def assign_visit(rexml_node, value)
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if value.is_a?(String)
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rexml_node.text = value
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elsif value.is_a?(REXML::Element)
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value.name = rexml_node.name
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raise "Node #{rexml_node.name} does not have a parent node" if rexml_node.parent.nil?
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rexml_node.parent.replace_child(rexml_node, value)
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raise 'Can only assign a String or a REXML::Element to an element'
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def retrieve_visit(rexml_node)
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# Stays on the same node in the dom
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def walk_visit(rexml_node)
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def assign_visit(rexml_node, value)
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raise 'Can only assign an attribute to an element.' if !rexml_node.is_a?(REXML::Element)
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rexml_node.attributes[@name] = value.to_s
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def retrieve_visit(rexml_node)
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raise 'Accessor not valid for paths with an attribute'
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def assert_true(expr)
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raise 'expected true' if !expr
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doc = REXML::Document.new()
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builder = XMLBuilder.new(doc)
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root_builder = builder['/root']
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root_builder['nested'] = 'more text'
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root_builder['/root/bnode'] = 'name'
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root_builder['/root/bnode/@attr'] = 'attr'
added
removed
lib/ec2/amitools/xmlbuilder.rb
