Class: Canon::Xml::SaxBuilder

Inherits:
Object
  • Object
show all
Defined in:
lib/canon/xml/sax_builder.rb

Overview

Builds Canon::Xml::Node tree from SAX events.

Engine-neutral: the event protocol is Nokogiri-shaped (qname + attribute pairs with xmlns declarations inline); Canon::Xml::Sax selects the driver. Much faster than DOM parsing + conversion — no intermediate engine DOM tree, no traversal conversion pass.

Usage:

root = SaxBuilder.parse(xml_string, preserve_whitespace: false)
# root is a Canon::Xml::Nodes::RootNode

For C14N, use strip_doctype: true to avoid DTD default attribute expansion:

root = SaxBuilder.parse(xml_string, strip_doctype: true)

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(preserve_whitespace: false) ⇒ SaxBuilder

Initialize the SAX builder

Parameters:

  • preserve_whitespace (Boolean) (defaults to: false) —

    Whether to preserve whitespace-only text nodes



75
76
77
78
79
80
81
82
83
84
85
86
87
 
# File 'lib/canon/xml/sax_builder.rb', line 75

def initialize(preserve_whitespace: false)
  @preserve_whitespace = preserve_whitespace
  @root = Nodes::RootNode.new
  @stack = [@root]
  # Track in-scope namespaces at each level
  # Each entry is a hash of prefix => uri
  @namespace_stack = [build_initial_namespaces]
  # Captured libxml errors during SAX parsing.  Surfaced on the
  # resulting RootNode so the diff report can warn the user
  # when a FATAL parse error has caused content loss
  # (see lutaml/canon#130).
  @parse_errors = []
end

Class Method Details

.parse(xml_string, preserve_whitespace: false, strip_doctype: false) ⇒ Nodes::RootNode

Parse XML string and return Canon::Xml::Node tree

Parameters:

  • xml_string (String) —

    XML content to parse

  • preserve_whitespace (Boolean) (defaults to: false) —

    Whether to preserve whitespace-only text nodes

  • strip_doctype (Boolean) (defaults to: false) —

    Strip DOCTYPE before parsing (for C14N to avoid DTD default attrs)

Returns:



26
27
28
29
30
31
32
33
34
35
36
37
38
 
# File 'lib/canon/xml/sax_builder.rb', line 26

def self.parse(xml_string, preserve_whitespace: false,
strip_doctype: false)
  # Strip DOCTYPE to prevent the SAX engine from expanding DTD default attributes
  # This is needed for C14N which should NOT include default attributes from DTD
  # Use string methods instead of complex regex to avoid ReDoS vulnerability
  if strip_doctype
    xml_string = strip_doctype_declaration(xml_string)
  end

  builder = new(preserve_whitespace: preserve_whitespace)
  Canon::Xml::Sax.parse(xml_string, builder)
  builder.result
end

.strip_doctype_declaration(xml) ⇒ String

Strip DOCTYPE declaration without using complex regex This avoids ReDoS vulnerability from patterns like \s+ and [^>]*

Parameters:

  • xml (String) —

    XML string potentially containing DOCTYPE

Returns:

  • (String) —

    XML string with DOCTYPE removed



45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
 
# File 'lib/canon/xml/sax_builder.rb', line 45

def self.strip_doctype_declaration(xml)
  # Find DOCTYPE start (case-insensitive)
  doctype_start = xml.upcase.index("<!DOCTYPE")
  return xml unless doctype_start

  # Find the end of DOCTYPE - it ends with >
  # Handle both simple DOCTYPE and those with internal subset [...]
  pos = doctype_start + 9 # length of "<!DOCTYPE"
  in_bracket = false

  while pos < xml.length
    char = xml[pos]
    if char == "[" && !in_bracket
      in_bracket = true
    elsif char == "]" && in_bracket
      in_bracket = false
    elsif char == ">" && !in_bracket
      # Found the end of DOCTYPE
      return xml[0...doctype_start] + xml[(pos + 1)..]
    end
    pos += 1
  end

  # If we didn't find a proper end, just return original
  xml
end

Instance Method Details

#cdata(string) ⇒ Object

Called for CDATA content. CDATA is literal character data: character references inside it are NOT decoded (a literal A stays as written), unlike regular text where they are resolved. Whitespace and adjacency rules match characters so the two forms of character data build identical trees.

Parameters:

  • string (String) —

    CDATA content



174
175
176
177
178
 
# File 'lib/canon/xml/sax_builder.rb', line 174

def cdata(string)
  return if string.nil?

  append_text(string, string)
end

#characters(string) ⇒ Object

Called for text content

Parameters:

  • string (String) —

    Text content



161
162
163
164
165
 
# File 'lib/canon/xml/sax_builder.rb', line 161

def characters(string)
  return if string.nil?

  append_text(decode_character_references(string), string)
end

#comment(string) ⇒ Object

Called for comments

Parameters:

  • string (String) —

    Comment content



226
227
228
229
230
 
# File 'lib/canon/xml/sax_builder.rb', line 226

def comment(string)
  parent = @stack.last
  comment_node = Nodes::CommentNode.new(value: string)
  parent.add_child(comment_node)
end

#end_element(_name) ⇒ Object

Called when an element ends

Parameters:

  • _name (String) —

    Element name (unused)



153
154
155
156
 
# File 'lib/canon/xml/sax_builder.rb', line 153

def end_element(_name)
  @stack.pop
  @namespace_stack.pop
end

#error(string) ⇒ Object

SAX callbacks for libxml errors and warnings. Without these overrides the default handlers swallow the events; with them, libxml's "Attribute xml:lang redefined" and similar messages land in @parse_errors and ride through to ComparisonResult.



93
94
95
 
# File 'lib/canon/xml/sax_builder.rb', line 93

def error(string)
  @parse_errors << string.to_s.strip
end

#processing_instruction(name, content) ⇒ Object

Called for processing instructions

Parameters:

  • name (String) —

    PI target

  • content (String) —

    PI content



236
237
238
239
240
241
 
# File 'lib/canon/xml/sax_builder.rb', line 236

def processing_instruction(name, content)
  parent = @stack.last
  pi = Nodes::ProcessingInstructionNode.new(target: name,
                                            data: content || "")
  parent.add_child(pi)
end

#reorder_children(root) ⇒ Object

Reorder root children so document element comes first followed by PIs and comments (outside document element)



257
258
259
260
261
262
263
 
# File 'lib/canon/xml/sax_builder.rb', line 257

def reorder_children(root)
  doc_element = root.children.find { |c| c.node_type == :element }
  return unless doc_element

  other_children = root.children.reject { |c| c.node_type == :element }
  root.children = [doc_element] + other_children
end

#result ⇒ Nodes::RootNode

Return the built tree

Returns:



246
247
248
249
250
251
252
253
 
# File 'lib/canon/xml/sax_builder.rb', line 246

def result
  # Reorder children so that the document element comes first,
  # followed by PIs and comments outside the document element
  # (C14N requires this ordering)
  reorder_children(@root)
  @root.parse_errors = @parse_errors if @parse_errors.any?
  @root
end

#start_element(name, attrs = []) ⇒ Object

Called when an element starts

Parameters:

  • name (String) —

    Element name (may include prefix like "ns:element")

  • attrs (Array) (defaults to: []) —

    Array of [name, value] pairs



105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
 
# File 'lib/canon/xml/sax_builder.rb', line 105

def start_element(name, attrs = [])
  parent = @stack.last

  # Parse namespace from name (prefix:localname or just localname)
  prefix, local_name = parse_qname(name)

  # Separate namespace declarations from regular attributes
  ns_decls, regular_attrs = separate_namespaces(attrs)

  # Check for relative namespace URIs (before building hash)
  # Convert to hash for iteration
  ns_hash = build_ns_hash(ns_decls)
  ns_hash.each_value do |uri|
    next if uri.nil? || uri.empty?

    if relative_uri?(uri)
      raise Canon::Error,
            "Relative namespace URI not allowed: #{uri}"
    end
  end

  # Push new namespace scope with declarations
  new_scope = @namespace_stack.last.merge(ns_hash)
  @namespace_stack.push(new_scope)

  # Find namespace URI from current scope
  ns_uri = new_scope[prefix.to_s]

  # Create element node
  element = Nodes::ElementNode.new(
    name: local_name,
    namespace_uri: ns_uri,
    prefix: prefix,
  )

  # Add namespace nodes from current scope
  add_namespace_nodes(element, new_scope)

  # Build and add attribute nodes (excluding xmlns declarations)
  add_attribute_nodes(element, regular_attrs)

  parent.add_child(element)
  @stack.push(element)
end

#warning(string) ⇒ Object 



97
98
99
 
# File 'lib/canon/xml/sax_builder.rb', line 97

def warning(string)
  @parse_errors << string.to_s.strip
end