class BufferedTokenizer

BufferedTokenizer takes a delimiter upon instantiation, or acts line-based by default. It allows input to be spoon-fed from some outside source which receives arbitrary length datagrams which may-or-may-not contain the token by which entities are delimited.

Commonly used to parse lines out of incoming data:

module LineBufferedConnection
  def receive_data(data)
    (@buffer ||= BufferedTokenizer.new).extract(data).each do |line|
      receive_line(line)
    end
  end
end

Public Class Methods

new(delimiter = "\n", size_limit = nil) click to toggle source

New BufferedTokenizers will operate on lines delimited by "n" by default or allow you to specify any delimiter token you so choose, which will then be used by String#split to tokenize the input data

# File lib/em/buftok.rb, line 36
def initialize(delimiter = "\n", size_limit = nil)
  # Store the specified delimiter
  @delimiter = delimiter

  # Store the specified size limitation
  @size_limit = size_limit

  # The input buffer is stored as an array.  This is by far the most efficient
  # approach given language constraints (in C a linked list would be a more
  # appropriate data structure).  Segments of input data are stored in a list
  # which is only joined when a token is reached, substantially reducing the
  # number of objects required for the operation.
  @input = []

  # Size of the input buffer
  @input_size = 0
end

Public Instance Methods

empty?() click to toggle source

Is the buffer empty?

# File lib/em/buftok.rb, line 135
def empty?
  @input.empty?
end

extract(data) click to toggle source

Extract takes an arbitrary string of input data and returns an array of tokenized entities, provided there were any available to extract. This makes for easy processing of datagrams using a pattern like:

tokenizer.extract(data).map { |entity| Decode(entity) }.each do ...

# File lib/em/buftok.rb, line 59
  def extract(data)
    # Extract token-delimited entities from the input string with the split command.
    # There's a bit of craftiness here with the -1 parameter.  Normally split would
    # behave no differently regardless of if the token lies at the very end of the 
    # input buffer or not (i.e. a literal edge case)  Specifying -1 forces split to
    # return "" in this case, meaning that the last entry in the list represents a
    # new segment of data where the token has not been encountered
    entities = data.split @delimiter, -1

    # Check to see if the buffer has exceeded capacity, if we're imposing a limit
    if @size_limit
      raise 'input buffer full' if @input_size + entities.first.size > @size_limit
      @input_size += entities.first.size
    end
    
    # Move the first entry in the resulting array into the input buffer.  It represents
    # the last segment of a token-delimited entity unless it's the only entry in the list.
    @input << entities.shift

    # If the resulting array from the split is empty, the token was not encountered
    # (not even at the end of the buffer).  Since we've encountered no token-delimited
    # entities this go-around, return an empty array.
    return [] if entities.empty?

    # At this point, we've hit a token, or potentially multiple tokens.  Now we can bring
    # together all the data we've buffered from earlier calls without hitting a token,
    # and add it to our list of discovered entities.
    entities.unshift @input.join

    # Note added by FC, 10Jul07. This paragraph contains a regression. It breaks
    # empty tokens. Think of the empty line that delimits an HTTP header. It will have
    # two "\n" delimiters in a row, and this code mishandles the resulting empty token.
    # It someone figures out how to fix the problem, we can re-enable this code branch.
    # Multi-character token support.
    # Split any tokens that were incomplete on the last iteration buf complete now.
    entities.map! do |e|
      e.split @delimiter, -1
    end
    # Flatten the resulting array.  This has the side effect of removing the empty
    # entry at the end that was produced by passing -1 to split.  Add it again if
    # necessary.
    if (entities[-1] == [])
      entities.flatten! << []
    else
      entities.flatten!
    end

    # Now that we've hit a token, joined the input buffer and added it to the entities
    # list, we can go ahead and clear the input buffer.  All of the segments that were
    # stored before the join can now be garbage collected.
    @input.clear
    
    # The last entity in the list is not token delimited, however, thanks to the -1
    # passed to split.  It represents the beginning of a new list of as-yet-untokenized  
    # data, so we add it to the start of the list.
    @input << entities.pop
    
    # Set the new input buffer size, provided we're keeping track
    @input_size = @input.first.size if @size_limit

    # Now we're left with the list of extracted token-delimited entities we wanted
    # in the first place.  Hooray!
    entities
  end

flush() click to toggle source

Flush the contents of the input buffer, i.e. return the input buffer even though a token has not yet been encountered

# File lib/em/buftok.rb, line 128
def flush
  buffer = @input.join
  @input.clear
  buffer
end