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require "ftw/namespace"
require "ftw/websocket"
# This class implements a parser for WebSocket messages over a stream.
#
# Protocol diagram copied from RFC6455
# 0 1 2 3
# 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
# +-+-+-+-+-------+-+-------------+-------------------------------+
# |F|R|R|R| opcode|M| Payload len | Extended payload length |
# |I|S|S|S| (4) |A| (7) | (16/64) |
# |N|V|V|V| |S| | (if payload len==126/127) |
# | |1|2|3| |K| | |
# +-+-+-+-+-------+-+-------------+ - - - - - - - - - - - - - - - +
# | Extended payload length continued, if payload len == 127 |
# + - - - - - - - - - - - - - - - +-------------------------------+
# | |Masking-key, if MASK set to 1 |
# +-------------------------------+-------------------------------+
# | Masking-key (continued) | Payload Data |
# +-------------------------------- - - - - - - - - - - - - - - - +
# : Payload Data continued ... :
# + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - +
# | Payload Data continued ... |
# +---------------------------------------------------------------+
#
# Example use:
#
# socket = FTW::Connection.new("example.com:80")
# parser = FTW::WebSocket::Parser.new
# # ... do HTTP Upgrade request to websockets
# loop do
# data = socket.sysread(4096)
# payload = parser.feed(data)
# if payload
# # We got a full websocket frame, print the payload.
# p :payload => payload
# end
# end
#
class FTW::WebSocket::Parser
# XXX: Implement control frames: http://tools.ietf.org/html/rfc6455#section-5.5
# States are based on the minimal unit of 'byte'
STATES = [ :flags_and_opcode, :mask_and_payload_init, :payload_length, :payload ]
private
# A new WebSocket protocol parser.
def initialize
@logger = Cabin::Channel.get
@opcode = 0
@masking_key = ""
@flag_final_payload = 0
@flag_mask = 0
transition(:flags_and_opcode, 1)
@buffer = ""
@buffer.force_encoding("BINARY")
end # def initialize
# Transition to a specified state and set the next required read length.
def transition(state, next_length)
@logger.debug("Transitioning", :transition => state, :nextlen => next_length)
@state = state
# TODO(sissel): Assert this self.respond_to?(state)
# TODO(sissel): Assert next_length is a number
need(next_length)
end # def transition
# Feed data to this parser.
#
# Currently, it will return the raw payload of websocket messages.
# Otherwise, it returns nil if no complete message has yet been consumed.
#
# @param [String] the string data to feed into the parser.
# @return [String, nil] the websocket message payload, if any, nil otherwise.
def feed(data)
@buffer << data
while have?(@need)
value = send(@state)
# Return if our state yields a value.
yield value if !value.nil? and block_given?
end
return nil
end # def <<
# Do we have at least 'length' bytes in the buffer?
def have?(length)
return length <= @buffer.bytesize
end # def have?
# Get 'length' string from the buffer.
def get(length=nil)
length = @need if length.nil?
data = @buffer[0 ... length]
@buffer = @buffer[length .. -1]
return data
end # def get
# Set the minimum number of bytes we need in the buffer for the next read.
def need(length)
@need = length
end # def need
# State: Flags (fin, etc) and Opcode.
# See: http://tools.ietf.org/html/rfc6455#section-5.3
def flags_and_opcode
# 0
# 0 1 2 3 4 5 6 7
# +-+-+-+-+-------
# |F|R|R|R| opcode
# |I|S|S|S| (4)
# |N|V|V|V|
# | |1|2|3|
byte = get(@need).bytes.first
@opcode = byte & 0xF # last 4 bites
@fin = (byte & 0x80 == 0x80)# first bit
#p :byte => byte, :bits => byte.to_s(2), :opcode => @opcode, :fin => @fin
# mask_and_payload_length has a minimum length
# of 1 byte, so start there.
transition(:mask_and_payload_init, 1)
# This state yields no output.
return nil
end # def flags_and_opcode
# State: mask_and_payload_init
# See: http://tools.ietf.org/html/rfc6455#section-5.2
def mask_and_payload_init
byte = get(@need).bytes.first
@masked = (byte & 0x80) == 0x80 # first bit (msb)
@payload_length = byte & 0x7F # remaining bits are the length
case @payload_length
when 126 # 2 byte, unsigned value is the payload length
transition(:extended_payload_length, 2)
when 127 # 8 byte, unsigned value is the payload length
transition(:extended_payload_length, 8)
else
# If there is a mask, read that next
if @masked
transition(:mask, 4)
else
# Otherwise, the payload is next.
# Keep the current payload length, a 7 bit value.
# Go to read the payload
transition(:payload, @payload_length)
end
end # case @payload_length
# This state yields no output.
return nil
end # def mask_and_payload_init
# State: payload_length
# This is the 'extended payload length' with support for both 16
# and 64 bit lengths.
# See: http://tools.ietf.org/html/rfc6455#section-5.2
def extended_payload_length
# 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
# +-+-+-+-+-------+-+-------------+-------------------------------+
# |F|R|R|R| opcode|M| Payload len | Extended payload length |
# |I|S|S|S| (4) |A| (7) | (16/64) |
# |N|V|V|V| |S| | (if payload len==126/127) |
# | |1|2|3| |K| | |
# +-+-+-+-+-------+-+-------------+ - - - - - - - - - - - - - - - +
# | Extended payload length continued, if payload len == 127 |
# + - - - - - - - - - - - - - - - +-------------------------------+
# | |Masking-key, if MASK set to 1 |
# +-------------------------------+-------------------------------+
data = get
case @need
when 2
@payload_length = data.unpack("S>").first
when 8
@payload_length = data.unpack("Q>").first
else
raise "Unknown payload_length byte length '#{@need}'"
end
if @masked
# Read the mask next if there is one.
transition(:mask, 4)
else
# Otherwise, next is the payload
transition(:payload, @payload_length)
end
# This state yields no output.
return nil
end # def extended_payload_length
# State: mask
# Read the mask key
def mask
# + - - - - - - - - - - - - - - - +-------------------------------+
# | |Masking-key, if MASK set to 1 |
# +-------------------------------+-------------------------------+
# | Masking-key (continued) | Payload Data |
# +-------------------------------- - - - - - - - - - - - - - - - +
@mask = get(@need)
transition(:payload, @payload_length)
return nil
end # def mask
# State: payload
# Read the full payload and return it.
# See: http://tools.ietf.org/html/rfc6455#section-5.3
def payload
# TODO(sissel): Handle massive payload lengths without exceeding memory.
# Perhaps if the payload is large (say, larger than 500KB by default),
# instead of returning the whole thing, simply return an Enumerable that
# yields chunks of the payload. There's no reason to buffer the entire
# thing. Have the consumer of this library make that decision.
data = get(@need)
transition(:flags_and_opcode, 1)
if @masked
return unmask(data, @mask)
else
return data
end
end # def payload
# Unmask the message using the key.
#
# For implementation specification, see
# http://tools.ietf.org/html/rfc6455#section-5.3
def unmask(message, key)
masked = []
mask_bytes = key.unpack("C4")
i = 0
message.each_byte do |byte|
masked << (byte ^ mask_bytes[i % 4])
i += 1
end
#p :unmasked => masked.pack("C*"), :original => message
return masked.pack("C*")
end # def unmask
public(:feed)
end # class FTW::WebSocket::Parser
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