Class: Apollo::Crawler::BaseCrawler

Inherits:
Object
  • Object
show all
Defined in:
lib/apollo_crawler/crawler/base_crawler.rb

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize ⇒ BaseCrawler

Returns a new instance of BaseCrawler.



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# File 'lib/apollo_crawler/crawler/base_crawler.rb', line 31

def initialize
  @backlog = []
end

Class Method Details

.create_metadoc(url, doc) ⇒ Object 



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# File 'lib/apollo_crawler/crawler/base_crawler.rb', line 160

def self.create_metadoc(url, doc)
  return {
    'url' => url,
    'doc' => doc.encode('UTF-8', {:invalid => :replace, :undef => :replace, :replace => '?'}),
    'hash' => Digest::SHA256.new.update(doc).hexdigest,
    'created_at' => Time.now.utc,
    'expires_at' => nil,
    'version' => 0
  }
end

.fetch(url) ⇒ Object 



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# File 'lib/apollo_crawler/crawler/base_crawler.rb', line 48

def self.fetch(url)
  RbConfig::DEFAULT_FETCHER.fetch(url)
end

.name_re ⇒ Object 



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# File 'lib/apollo_crawler/crawler/base_crawler.rb', line 35

def self.name_re()
  return /crawler$/
end

.try_get_doc(root, url) ⇒ Object 



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# File 'lib/apollo_crawler/crawler/base_crawler.rb', line 60

def self.try_get_doc(root, url)
  doc = BaseCrawler.try_get_url(root, url)
  
  # TODO: Set experition header
  return {
    :doc => doc,
    :url => url
  }
end

.try_get_url(root, url) ⇒ Object 



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# File 'lib/apollo_crawler/crawler/base_crawler.rb', line 52

def self.try_get_url(root, url)
  begin
    return URI.join(root, url)
  rescue
    return nil
  end
end

Instance Method Details

#etl(url = nil, opts = {}, &block) ⇒ Object

  • (0) Figure out URL

  • (1) Extract Data

  • (2) Extract Links

  • (3) Go to (0) eventually



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# File 'lib/apollo_crawler/crawler/base_crawler.rb', line 74

def etl(url=nil, opts={}, &block)
  # Look for passed URL use default instead and fail if it is not valid
  if(url.nil? || url.empty?)
    url = self.url
  end

  # TODO: Be more agressive, use assert, it is clients responsibility!
  if(url.nil?)
    return nil
  end

  # We support both - list of urls or single url
  if(url.kind_of?(Array))
    @backlog.concat(url)
  else
    @backlog << url
  end

  # Counter of processed documents (pages)
  docs_processed = 0

  res = []
  # TODO: Respect limit of documents/urls processed
  while(@backlog.empty? == false)
    url = @backlog.shift

    # puts "Processing '#{url}'"
    doc = self.process_url(url)
    
    # Increase counter of processed documents
    docs_processed = docs_processed + 1

    # Process document if was successfuly retreived
    if(!doc.nil?)
      # TODO: Use log4r and log it only on info level
      if block_given?
        yield doc
      end

      # Add document to queue of results
      res << doc

      # If
      if(doc[:links].nil? == false)
        doc[:links].each do |link|
          url = link[:link].to_s
          # TODO: Use log4r and log it only on info level
          #puts url

          # TODO: Check if it is unique
          @backlog << url
        end
      end
    end

    # Break if limit of documents to processed was reached
    break if opts[:doc_limit] && docs_processed >= opts[:doc_limit]
  end
  return res
end

#extract_data(doc) ⇒ Object

Extracts data from document



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# File 'lib/apollo_crawler/crawler/base_crawler.rb', line 212

def extract_data(doc)
  res = []
  return res
end

#extract_links(doc) ⇒ Object

Extract links to another documents from this document



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# File 'lib/apollo_crawler/crawler/base_crawler.rb', line 218

def extract_links(doc)
  res = []
  return res
end

#fetch_document(url) ⇒ Object

Fetch document



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# File 'lib/apollo_crawler/crawler/base_crawler.rb', line 172

def fetch_document(url)
  # TODO: Refactor following idiom
  if(url == nil)
    url = self.url
  end

  if(url.nil?)
    return nil
  end

  # TODO: Use some (custom-made) low-level HTTTP Protocol cache - just for sure
  cache = Apollo::Cache::Factory.instance.construct
  metadoc = cache.get(url) do
    max_attempts = 3
    attempt_no = 0
    success = false
    
    doc = nil
    while(attempt_no < max_attempts && success == false) do
      begin
        doc = BaseCrawler.fetch(url)
        success = true
      rescue Exception => e
        puts "EXCEPTION: Unable to fetch '#{url}', reason: '#{e.to_s}'"
        sleep 1

        attempt_no = attempt_no + 1
        success = false
      end
    end

    # Create metadata
    BaseCrawler.create_metadoc(url, doc)
  end

  # TODO: Encapsulate and make more robust => invalid hostname, timeouts and so
  return Nokogiri::HTML(metadoc['doc'])
end

#name ⇒ Object

Name of the crawler



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# File 'lib/apollo_crawler/crawler/base_crawler.rb', line 40

def name
  return "Crawler Base" 
end

#process_url(url) ⇒ Object 



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# File 'lib/apollo_crawler/crawler/base_crawler.rb', line 135

def process_url(url)
  doc = self.fetch_document(url)
  if(doc.nil?)
    return nil
  end

  # Try extract data from document
  data = self.extract_data(doc)

  # Try extract links for another documents 
  links = self.extract_links(doc)
  
  # TODO: Make configurable if links extracted from doc should be printed
  # puts links.inspect

  # Format ETL result
  res = { 
    :crawler => self.class.name,
    :data => data,
    :links => links
  }

  return res
end

#url ⇒ Object 



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# File 'lib/apollo_crawler/crawler/base_crawler.rb', line 44

def url
  return nil
end