Class: JsonProjection::Parser

Inherits:
Object
  • Object
show all
Defined in:
lib/json-projection/parser.rb

Overview

A streaming JSON parser that generates SAX-like events for state changes. Use the json gem for small documents. Use this for huge documents that won’t fit in memory.

Constant Summary collapse

CONTROL = 
/[\x00-\x1F]/
WS = 
/[ \n\t\r]/
HEX = 
/[0-9a-fA-F]/
DIGIT = 
/[0-9]/
DIGIT_1_9 = 
/[1-9]/
DIGIT_END = 
/\d$/
TRUE_RE = 
/[rue]/
FALSE_RE = 
/[alse]/
NULL_RE = 
/[ul]/
TRUE_KEYWORD = 
'true'
FALSE_KEYWORD = 
'false'
NULL_KEYWORD = 
'null'
LEFT_BRACE = 
'{'
RIGHT_BRACE = 
'}'
LEFT_BRACKET = 
'['
RIGHT_BRACKET = 
']'
BACKSLASH = 
'\\'
SLASH = 
'/'
QUOTE = 
'"'
COMMA = 
','
COLON = 
':'
ZERO = 
'0'
MINUS = 
'-'
PLUS = 
'+'
POINT = 
'.'
EXPONENT = 
/[eE]/

Instance Method Summary collapse

Constructor Details

#initialize(stream, chunk_size = 4096) ⇒ Parser

Initialize a new parser with a stream. The stream cursor is advanced as events are drawn from the parser. The parser maintains a small data cache of bytes read from the stream.

stream

IO IO stream to read data from.

chunk_size

Integer Number of bytes to read from the stream at a time.

Returns nothing.



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# File 'lib/json-projection/parser.rb', line 76

def initialize(stream, chunk_size = 4096)
  @stream = stream
  @chunk_size = chunk_size

  @event_buffer = Fifo.new

  @character_buffer = Buffer.new

  @characters_cursor = -1
  @characters = nil

  @stream_position = -1
  @state = :start_document
  @stack = []

  @value_buffer = ""
  @unicode = ""
end

Instance Method Details

#next_event ⇒ Object

Draw bytes from the stream until an event can be constructed. May raise IO errors.

Returns a JsonProject::StreamEvent subclass or raises StandardError.



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# File 'lib/json-projection/parser.rb', line 99

def next_event()
  # Are there any already read events, return the oldest
  event = @event_buffer.pop!
  return event unless event.nil?

  if @state == :end_document
    error("already EOF, no more events")
  end

  while true do
    if @characters.nil? || @characters_cursor == @characters.size
      data = stream.read(@chunk_size)
      if data == nil # hit EOF
        error("unexpected EOF")
      end

      @characters = @character_buffer.<<(data).each_char.to_a
      @characters_cursor = 0
    end

    character = @characters[@characters_cursor]
    @characters_cursor += 1

    @stream_position += 1

    new_state, new_events = handle_character(@state, character)

    @state = new_state
    @event_buffer.prepend!(new_events)

    event = @event_buffer.pop!
    return event unless event.nil?
  end
end