require "ftw/namespace" require "ftw/websocket" require "ftw/singleton" require "ftw/websocket/constants" # This class implements a writer 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 ... | # +---------------------------------------------------------------+ class FTW::WebSocket::Writer include FTW::WebSocket::Constants extend FTW::Singleton # VALID_MODES = [:server, :client] private # Write the given text in a websocket frame to the connection. # # Valid 'mode' settings are :server or :client. If :client, the # payload will be masked according to RFC6455 section 5.3: # http://tools.ietf.org/html/rfc6455#section-5.3 def write_text(connection, text, mode=:server) if !VALID_MODES.include?(mode) raise InvalidArgument.new("Invalid message mode: #{mode}, expected one of" \ "#{VALID_MODES.inspect}") end data = [] pack = [] # For now, assume single-fragment, text frames pack_opcode(data, pack, OPCODE_TEXT) pack_payload(data, pack, text, mode) connection.write(data.pack(pack.join(""))) end # def write_text def pack_opcode(data, pack, opcode) # Pack the first byte (fin + opcode) data << ((1 << 7) | opcode) pack << "C" end # def pack_opcode def pack_payload(data, pack, text, mode) pack_maskbit_and_length(data, pack, text.length, mode) pack_extended_length(data, pack, text.length) if text.length > 126 if mode == :client mask_key = [rand(1 << 32)].pack("Q") pack_mask(data, pack, mask_key) data << mask(text, mask_key) pack << "A*" else data << text pack << "A*" end end # def pack_payload # Implement masking as described by http://tools.ietf.org/html/rfc6455#section-5.3 # Basically, we take a 4-byte random string and use it, round robin, to XOR # every byte. Like so: # message[0] ^ key[0] # message[1] ^ key[1] # message[2] ^ key[2] # message[3] ^ key[3] # message[4] ^ key[0] # ... def mask(message, key) masked = [] mask_bytes = key.unpack("C4") i = 0 message.each_byte do |byte| masked << (byte ^ mask_bytes[i % 4]) i += 1 end return masked.pack("C*") end # def mask def pack_maskbit_and_length(data, pack, length, mode) # Pack mask + payload length maskbit = (mode == :client) ? (1 << 7) : 0 if length >= 126 if length < (1 << 16) # if less than 2^16, use 2 bytes lengthbits = 126 else lengthbits = 127 end else lengthbits = length end data << (maskbit | lengthbits) pack << "C" end public(:initialize, :write_text) end # module FTW::WebSocket::Writer