Class: JSON::Stream::Parser

Inherits:
Object
  • Object
show all
Defined in:
lib/json/stream/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

BUF_SIZE = 
512
CONTROL = 
/[[:cntrl:]]/
WS = 
/\s/
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]/

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(&block) ⇒ Parser

Create a new parser with an optional initialization block where we can register event callbacks. For example: parser = JSON::Stream::Parser.new do

start_document { puts "start document" }
end_document   { puts "end document" }
start_object   { puts "start object" }
end_object     { puts "end object" }
start_array    { puts "start array" }
end_array      { puts "end array" }
key            {|k| puts "key: #{k}" }
value          {|v| puts "value: #{v}" }

end



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# File 'lib/json/stream/parser.rb', line 84

def initialize(&block)
  @state = :start_document
  @utf8 = Buffer.new
  @listeners = Hash.new {|h, k| h[k] = [] }
  @stack, @unicode, @buf, @pos = [], "", "", -1
  instance_eval(&block) if block_given?
end

Class Method Details

.parse(json) ⇒ Object

Parses a full JSON document from a String or an IO stream and returns the parsed object graph. For parsing small JSON documents with small memory requirements, use the json gem’s faster JSON.parse method instead.



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# File 'lib/json/stream/parser.rb', line 44

def self.parse(json)
  stream = json.is_a?(String) ? StringIO.new(json) : json
  parser = Parser.new
  builder = Builder.new(parser)
  while (buf = stream.read(BUF_SIZE)) != nil
    parser << buf
  end
  raise ParserError, "unexpected eof" unless builder.result
  builder.result
ensure
  stream.close
end

Instance Method Details

#<<(data) ⇒ Object

Pass data into the parser to advance the state machine and generate callback events. This is well suited for an EventMachine receive_data loop.



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# File 'lib/json/stream/parser.rb', line 95

def <<(data)
  (@utf8 << data).each_char do |ch|
    @pos += 1
    case @state
    when :start_document
      case ch
      when LEFT_BRACE
        @state = :start_object
        @stack.push(:object)
        notify_start_document
        notify_start_object
      when LEFT_BRACKET
        @state = :start_array
        @stack.push(:array)
        notify_start_document
        notify_start_array
      when WS
        # ignore
      else
        error("Expected object or array start")
      end
    when :start_object
      case ch
      when RIGHT_BRACE
        end_container(:object)
      when QUOTE
        @state = :start_string
        @stack.push(:key)
      when WS
        # ignore
      else
        error("Expected object key start")
      end
    when :start_string
      case ch
      when QUOTE
        if @stack.pop == :string
          @state = :end_value
          notify_value(@buf)
        else # :key
          @state = :end_key
          notify_key(@buf)
        end
        @buf = ""
      when BACKSLASH
        @state = :start_escape
      when CONTROL
        error('Control characters must be escaped')
      else
        @buf << ch
      end
    when :start_escape
      case ch
      when QUOTE, BACKSLASH, SLASH
        @buf << ch
        @state = :start_string
      when B
        @buf << "\b"
        @state = :start_string
      when F
        @buf << "\f"
        @state = :start_string
      when N
        @buf << "\n"
        @state = :start_string
      when R
        @buf << "\r"
        @state = :start_string
      when T
        @buf << "\t"
        @state = :start_string
      when U
        @state = :unicode_escape
      else
        error("Expected escaped character")
      end
    when :unicode_escape
      case ch
      when HEX
        @unicode << ch
        if @unicode.size == 4
          codepoint = @unicode.slice!(0, 4).hex
          if codepoint >= 0xD800 && codepoint <= 0xDBFF
            error('Expected low surrogate pair half') if @stack[-1].is_a?(Fixnum)
            @state = :start_surrogate_pair
            @stack.push(codepoint)
          elsif codepoint >= 0xDC00 && codepoint <= 0xDFFF
            high = @stack.pop
            error('Expected high surrogate pair half') unless high.is_a?(Fixnum)
            pair = ((high - 0xD800) * 0x400) + (codepoint - 0xDC00) + 0x10000
            @buf << pair
            @state = :start_string
          else
            @buf << codepoint
            @state = :start_string
          end
        end
      else
        error('Expected unicode escape hex digit')
      end
    when :start_surrogate_pair
      case ch
      when BACKSLASH 
        @state = :start_surrogate_pair_u
      else
        error('Expected low surrogate pair half')
      end
    when :start_surrogate_pair_u
      case ch
      when U
        @state = :unicode_escape
      else
        error('Expected low surrogate pair half')
      end
    when :start_negative_number
      case ch
      when ZERO
        @state = :start_zero
        @buf << ch
      when DIGIT_1_9
        @state = :start_int
        @buf << ch
      else
        error('Expected 0-9 digit')
      end
    when :start_zero
      case ch
      when POINT
        @state = :start_float
        @buf << ch
      when EXPONENT
        @state = :start_exponent
        @buf << ch
      else
        @state = :end_value
        notify_value(@buf.to_i)
        @buf = ""
        @pos -= 1
        redo
      end
    when :start_float
      case ch
      when DIGIT
        @state = :in_float
        @buf << ch
      else
        error('Expected 0-9 digit')
      end
    when :in_float
      case ch
      when DIGIT
        @buf << ch
      when EXPONENT
        @state = :start_exponent
        @buf << ch
      else
        @state = :end_value
        notify_value(@buf.to_f)
        @buf = ""
        @pos -= 1
        redo
      end
    when :start_exponent
      case ch
      when MINUS, PLUS, DIGIT
        @state = :in_exponent
        @buf << ch
      else
        error('Expected +, -, or 0-9 digit')
      end
    when :in_exponent
      case ch
      when DIGIT
        @buf << ch
      else
        error('Expected 0-9 digit') unless @buf =~ DIGIT_END
        @state = :end_value
        num = @buf.include?('.') ? @buf.to_f : @buf.to_i
        notify_value(num)
        @buf = ""
        @pos -= 1
        redo
      end
    when :start_int
      case ch
      when DIGIT
        @buf << ch
      when POINT
        @state = :start_float
        @buf << ch
      when EXPONENT
        @state = :start_exponent
        @buf << ch
      else
        @state = :end_value
        notify_value(@buf.to_i)
        @buf = ""
        @pos -= 1
        redo
      end
    when :start_true
      keyword(TRUE_KEYWORD, true, TRUE_RE, ch)
    when :start_false
      keyword(FALSE_KEYWORD, false, FALSE_RE, ch)
    when :start_null
      keyword(NULL_KEYWORD, nil, NULL_RE, ch)
    when :end_key
      case ch
      when COLON
        @state = :key_sep
      when WS
        # ignore
      else
        error("Expected colon key separator")
      end
    when :key_sep
      start_value(ch)
    when :start_array
      case ch
      when RIGHT_BRACKET
        end_container(:array)
      when WS
        # ignore
      else
        start_value(ch)
      end
    when :end_value
      case ch
      when COMMA
        @state = :value_sep
      when RIGHT_BRACKET
        end_container(:array)
      when RIGHT_BRACE
        end_container(:object)
      when WS
        # ignore
      else
        error("Expected comma or object or array close")
      end
    when :value_sep
      if @stack[-1] == :object
        case ch
        when QUOTE
          @state = :start_string
          @stack.push(:key)
        when WS
          # ignore
        else
          error("Expected object key start")
        end
      else
        start_value(ch)
      end
    when :end_document
      error("Unexpected data") unless ch =~ WS
    end
  end
end