WebSocket: Ruby parsing library

The WebSocket protocol establishes a two-way communication channel via TCP. Messages are made up of one or more dataframes, and are delineated by frames with the fin bit set.

KS implementation details

License: CC0-1.0

References

This page hosts a formal specification of WebSocket using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.

Usage

Runtime library

All parsing code for Ruby generated by Kaitai Struct depends on the Ruby runtime library. You have to install it before you can parse data.

The Ruby runtime library can be installed from RubyGems:

gem install kaitai-struct

Code

Parse a local file and get structure in memory:

data = Websocket.from_file("path/to/local/file.WebSocket")

Or parse structure from a string of bytes:

bytes = "\x00\x01\x02..."
data = Websocket.new(Kaitai::Struct::Stream.new(bytes))

After that, one can get various attributes from the structure by invoking getter methods like:

data.initial_frame # => get initial frame

Ruby source code to parse WebSocket

websocket.rb

# This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild

require 'kaitai/struct/struct'

unless Gem::Version.new(Kaitai::Struct::VERSION) >= Gem::Version.new('0.9')
  raise "Incompatible Kaitai Struct Ruby API: 0.9 or later is required, but you have #{Kaitai::Struct::VERSION}"
end


##
# The WebSocket protocol establishes a two-way communication channel via TCP.
# Messages are made up of one or more dataframes, and are delineated by
# frames with the `fin` bit set.
class Websocket < Kaitai::Struct::Struct

  OPCODE = {
    0 => :opcode_continuation,
    1 => :opcode_text,
    2 => :opcode_binary,
    3 => :opcode_reserved_3,
    4 => :opcode_reserved_4,
    5 => :opcode_reserved_5,
    6 => :opcode_reserved_6,
    7 => :opcode_reserved_7,
    8 => :opcode_close,
    9 => :opcode_ping,
    10 => :opcode_pong,
    11 => :opcode_reserved_control_b,
    12 => :opcode_reserved_control_c,
    13 => :opcode_reserved_control_d,
    14 => :opcode_reserved_control_e,
    15 => :opcode_reserved_control_f,
  }
  I__OPCODE = OPCODE.invert
  def initialize(_io, _parent = nil, _root = self)
    super(_io, _parent, _root)
    _read
  end

  def _read
    @initial_frame = InitialFrame.new(@_io, self, @_root)
    if initial_frame.header.finished != true
      @trailing_frames = []
      i = 0
      begin
        _ = Dataframe.new(@_io, self, @_root)
        @trailing_frames << _
        i += 1
      end until _.header.finished
    end
    self
  end
  class FrameHeader < Kaitai::Struct::Struct
    def initialize(_io, _parent = nil, _root = self)
      super(_io, _parent, _root)
      _read
    end

    def _read
      @finished = @_io.read_bits_int_be(1) != 0
      @reserved = @_io.read_bits_int_be(3)
      @opcode = Kaitai::Struct::Stream::resolve_enum(Websocket::OPCODE, @_io.read_bits_int_be(4))
      @is_masked = @_io.read_bits_int_be(1) != 0
      @len_payload_primary = @_io.read_bits_int_be(7)
      @_io.align_to_byte
      if len_payload_primary == 126
        @len_payload_extended_1 = @_io.read_u2be
      end
      if len_payload_primary == 127
        @len_payload_extended_2 = @_io.read_u4be
      end
      if is_masked
        @mask_key = @_io.read_u4be
      end
      self
    end
    def len_payload
      return @len_payload unless @len_payload.nil?
      @len_payload = (len_payload_primary <= 125 ? len_payload_primary : (len_payload_primary == 126 ? len_payload_extended_1 : len_payload_extended_2))
      @len_payload
    end
    attr_reader :finished
    attr_reader :reserved
    attr_reader :opcode
    attr_reader :is_masked
    attr_reader :len_payload_primary
    attr_reader :len_payload_extended_1
    attr_reader :len_payload_extended_2
    attr_reader :mask_key
  end
  class InitialFrame < Kaitai::Struct::Struct
    def initialize(_io, _parent = nil, _root = self)
      super(_io, _parent, _root)
      _read
    end

    def _read
      @header = FrameHeader.new(@_io, self, @_root)
      if header.opcode != :opcode_text
        @payload_bytes = @_io.read_bytes(header.len_payload)
      end
      if header.opcode == :opcode_text
        @payload_text = (@_io.read_bytes(header.len_payload)).force_encoding("UTF-8")
      end
      self
    end
    attr_reader :header
    attr_reader :payload_bytes
    attr_reader :payload_text
  end
  class Dataframe < Kaitai::Struct::Struct
    def initialize(_io, _parent = nil, _root = self)
      super(_io, _parent, _root)
      _read
    end

    def _read
      @header = FrameHeader.new(@_io, self, @_root)
      if _root.initial_frame.header.opcode != :opcode_text
        @payload_bytes = @_io.read_bytes(header.len_payload)
      end
      if _root.initial_frame.header.opcode == :opcode_text
        @payload_text = (@_io.read_bytes(header.len_payload)).force_encoding("UTF-8")
      end
      self
    end
    attr_reader :header
    attr_reader :payload_bytes
    attr_reader :payload_text
  end
  attr_reader :initial_frame
  attr_reader :trailing_frames
end