Class: Traject::NokogiriReader

Inherits:
Object
  • Object
show all
Includes:
Enumerable
Defined in:
lib/traject/nokogiri_reader.rb

Overview

A Trajet reader which reads XML, and yields zero to many Nokogiri::XML::Document objects as source records in the traject pipeline.

It does process the entire input document with Nokogiri::XML.parse, DOM-parsing, so will take RAM for the entire input document, until iteration completes. (There is a separate half-finished ExperimentalStreamingNokogiriReader available, but it is experimental, half-finished, may disappear or change in backwards compat at any time, problematic, not recommended for production use, etc.)

You can have it yield the entire input XML as a single traject source record (default), or you can use setting nokogiri.each_record_xpath to split the source up into separate records to yield into traject pipeline -- each one will be it's own Nokogiri::XML::Document.

Settings

  • nokogiri.default_namespaces: Set namespace prefixes that can be used in other settings, including extract_xpath from NokogiriMacros.
  • nokogiri.each_record_xpath: if set to a string xpath, will take all matching nodes from the input doc, and yield the individually as source records to the pipeline. If you need to use namespaces here, you need to have them registered with nokogiri.default_namespaces. If your source docs use namespaces, you DO need to use them in your each_record_xpath.
  • nokogiri.strict_mode: if set to true or "true", ask Nokogiri to parse in 'strict' mode, it will raise a Nokogiri::XML::SyntaxError if the XML is not well-formed, instead of trying to take it's best-guess correction. https://nokogiri.org/tutorials/ensuring_well_formed_markup.html
  • nokogiri_reader.extra_xpath_hooks: Experimental in progress, see below.

nokogiri_reader.extra_xpath_hooks: For handling nodes outside of your each_record_xpath

What if you want to use each_record_xpath to yield certain nodes as source documents, but there is additional some other info in other parts of the input document you need? This came up when developing the OaiPmhNokogiriReader, which yields "//oai:record" as pipeline source documents, but also needed to look at "//oai:resumptionToken" to scrape the entire results.

There is a semi-finished/in-progress feature that meets that use case -- unclear if it will meet all use cases for this general issue.

Setting nokogiri_reader.extra_xpath_hooks can be set to a Hash where the keys are xpaths (if using namespaces must be must be registered with nokogiri.default_namespaces), and the value is a lambda/ proc/callable object, taking two arguments.

provide "nokogiri_reader.extra_xpath_hooks", {
  "//oai:resumptionToken" =>
    lambda do |node, clipboard|
      clipboard[:resumption_token] = node.text
    end"
}

The first arg is the matching node. What's this clipboard? Well, what are you gonna do with what you get out of there, that you can do in a thread-safe way in the middle of nokogiri processing? The second arg is a thread-safe Hash "clipboard" that you can store things in, and later access via reader.clipboard.

There's no great thread-safe way to get reader.clipboard in a normal nokogiri pipeline though, (the reader can change in multi-file handling so there can be a race condition if you try naively, don't!) Which is why this feature needs some work for general applicability. The OaiPmhReader manually creates it's readers outside the usual nokogiri flow, so can use it.

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(input_stream, settings) ⇒ NokogiriReader

Returns a new instance of NokogiriReader.


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# File 'lib/traject/nokogiri_reader.rb', line 64

def initialize(input_stream, settings)
  @settings = Traject::Indexer::Settings.new settings
  @input_stream = input_stream
  @clipboard = Traject::Util.is_jruby? ? Concurrent::Map.new : Concurrent::Hash.new

  default_namespaces # trigger validation
  validate_xpath(each_record_xpath, key_name: "each_record_xpath") if each_record_xpath
  extra_xpath_hooks.each_pair do |xpath, _callable|
    validate_xpath(xpath, key_name: "extra_xpath_hooks")
  end
end

Instance Attribute Details

#clipboardObject (readonly)

Returns the value of attribute clipboard


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# File 'lib/traject/nokogiri_reader.rb', line 62

def clipboard
  @clipboard
end

#input_streamObject (readonly)

Returns the value of attribute input_stream


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# File 'lib/traject/nokogiri_reader.rb', line 62

def input_stream
  @input_stream
end

#path_trackerObject (readonly)

Returns the value of attribute path_tracker


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# File 'lib/traject/nokogiri_reader.rb', line 62

def path_tracker
  @path_tracker
end

#settingsObject (readonly)

Returns the value of attribute settings


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# File 'lib/traject/nokogiri_reader.rb', line 62

def settings
  @settings
end

Instance Method Details

#default_namespacesObject


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# File 'lib/traject/nokogiri_reader.rb', line 84

def default_namespaces
  @default_namespaces ||= (settings["nokogiri.namespaces"] || {}).tap { |ns|
    unless ns.kind_of?(Hash)
      raise ArgumentError, "nokogiri.namespaces must be a hash, not: #{ns.inspect}"
    end
  }
end

#eachObject


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# File 'lib/traject/nokogiri_reader.rb', line 92

def each
  config_proc = if settings["nokogiri.strict_mode"]
    proc { |config| config.strict }
  end

  whole_input_doc = Nokogiri::XML.parse(input_stream, &config_proc)

  if each_record_xpath
    whole_input_doc.xpath(each_record_xpath, default_namespaces).each do |matching_node|
      # We want to take the matching node, and make it into root in a new Nokogiri document.
      # This is tricky to do as performant as possible (we want to re-use the existing libxml node),
      # while preserving namespaces properly (especially in jruby). Some uses of noko api that seem
      # like they should work don't, esp in jruby.
      child_doc = Nokogiri::XML::Document.new

      reparent_node_to_root(child_doc, matching_node)

      yield child_doc

      child_doc = nil # hopefully make things easier on the GC.
    end
  else
    # caller wants whole doc as a traject source record
    yield whole_input_doc
  end

  run_extra_xpath_hooks(whole_input_doc)

ensure
  # hopefully make things easier on the GC.
  whole_input_doc = nil
end

#each_record_xpathObject


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# File 'lib/traject/nokogiri_reader.rb', line 76

def each_record_xpath
  @each_record_xpath ||= settings["nokogiri.each_record_xpath"]
end

#extra_xpath_hooksObject


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# File 'lib/traject/nokogiri_reader.rb', line 80

def extra_xpath_hooks
  @extra_xpath_hooks ||= settings["nokogiri_reader.extra_xpath_hooks"] || {}
end