Initial work on UDP mode ICMP ping (https://keith.github.io/xcode-man-pages/icmp.4.html#Non-privileged_ICMP)

lib/ping.rb

@@ -0,0 +1,70 @@
+require "socket"
+
+ICMPHeader = Data.define(:type, :code, :checksum, :_ping_id, :_sequence_id, :data)
+
+ICMP_ECHOREPLY = 0 # Echo reply
+ICMP_ECHO      = 8 # Echo request
+ICMP_SUBCODE   = 0
+
+# Perform a checksum on the message.  This is the sum of all the short
+# words and it folds the high order bits into the low order bits.
+#
+def checksum(msg)
+  length    = msg.length
+  num_short = length / 2
+  check     = 0
+
+  msg.unpack("n#{num_short}").each do |short|
+    check += short
+  end
+
+  if (length % 2).positive?
+    check += msg[length-1, 1].unpack1("C") << 8
+  end
+
+  check = (check >> 16) + (check & 0xffff)
+  ~((check >> 16) + check) & 0xffff
+end
+
+ip_address = "127.0.0.1" # "example.com" # "timecrafters.org" #
+@ping_id = 92_459_064_892 & 0xffff
+@sequence = 1 % 65_536
+data = ""
+data_size = 56
+data_size.times { |n| data << (n % 256).chr }
+
+check = 0
+packer = "C2 n3 A" << data_size.to_s
+message = [ICMP_ECHO, ICMP_SUBCODE, check, @ping_id, @sequence, data].pack(packer)
+check = checksum(message)
+message = [ICMP_ECHO, ICMP_SUBCODE, check, @ping_id, @sequence, data].pack(packer)
+message_header = ICMPHeader.new(*[ICMP_ECHO, ICMP_SUBCODE, check, @ping_id, @sequence, data])
+socket = Socket.new(Socket::AF_INET, Socket::SOCK_DGRAM, Socket::IPPROTO_ICMP)
+socket.send(message, 0, Socket.pack_sockaddr_in(0, ip_address))
+s = Time.now
+loop do
+  data, _addrinfo = socket.recvfrom(1500)
+  pp [message, data]
+  header = ICMPHeader.new(*data.unpack("C2 n3 A*"))
+  pp [message_header, header]
+  # reply_type = data[20, 2].unpack1("C2")
+  # pp reply_type
+
+  ping_id = header._ping_id
+  sequence = header._sequence_id
+
+  case header.type
+  when ICMP_ECHOREPLY
+    puts "ECHOREPLY"
+  end
+
+  pp [@ping_id, ping_id]
+  pp [@sequence, sequence]
+
+  if ping_id == @ping_id && sequence == @sequence && reply_type == ICMP_ECHOREPLY
+    puts "PING OKAY: #{Time.now - s}s"
+    break
+  end
+
+  break
+end