Make correct mask when converting IPv4 <=> IPv6

[Tietew]

When converting IPv4 to/from IPv6, IPAddr#set generates incorrect mask value.
This causes IPAddr#include? returns incorrect result.

ip4 = IPAddr.new('::ffff:127.0.0.1').native
p [ip4.to_s, ip4.prefix]
ip6 = IPAddr.new('127.0.0.1').ipv4_mapped
p [ip6.to_s, ip6.prefix]

Expected

["127.0.0.1", 32]
["::ffff:127.0.0.1", 128]

Actual

["127.0.0.1", -96]       # @mask_addr == 0xFFFFFFFFFFFFFFFF
["::ffff:127.0.0.1", 0]  # @mask_addr == 0x000000000000FFFF

[ioquatix]

@Tietew can you rebase on master.

[Tietew]

@ioquatix done.

[ioquatix]

Can you please squash typo fix.

[taketo1113]

#native / #ipv4_mapped (fixed)

In ipaddr v1.2.7, these methods have already been fixed and now behave as expected:

IPAddr::VERSION
=> "1.2.7"

ip4 = IPAddr.new('::ffff:127.0.0.1').native
=> #<IPAddr: IPv4:127.0.0.1/255.255.255.255>
p [ip4.to_s, ip4.prefix]
["127.0.0.1", 32]

ip6 = IPAddr.new('127.0.0.1').ipv4_mapped
=> #<IPAddr: IPv6:0000:0000:0000:0000:0000:ffff:7f00:0001/ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff>
p [ip6.to_s, ip6.prefix]
["::ffff:127.0.0.1", 128]

These fixes were introduced in ipaddr v1.2.4 in the following Pull Requests:
https://github.com/ruby/ipaddr/releases/tag/v1.2.4

• Ipaddr#native must also coerce @mask_addr #34 fixed #native.
• Fix include? and ipv4_mapped to allow drb tests to pass #31 fixed #ipv4_mapped.

#ipv4_compat (still broken)

However, #ipv4_compat still returns incorrect values for #prefix:

ip4 = IPAddr.new('192.168.1.1').ipv4_compat
=> #<IPAddr: IPv6:0000:0000:0000:0000:0000:0000:c0a8:0101/0000:0000:0000:0000:0000:0000:ffff:ffff>
p [ip4.to_s, ip4.prefix]
["::192.168.1.1", 0] # expected ["::192.168.1.1", 128]

ip4 = IPAddr.new('192.168.0.0/16').ipv4_compat
=> #<IPAddr: IPv6:0000:0000:0000:0000:0000:0000:c0a8:0000/0000:0000:0000:0000:0000:0000:ffff:0000>
p [ip4.to_s, ip4.prefix]
["::192.168.0.0", 0] # expected ["::192.168.0.0", 112]

NOTE: fix #ipv4_compat

Since the implementation of lib/ipaddr.rb has changed from when this Pull Request was first created, the following patch can be applied to fix #ipv4_compat so that it behaves as expected:

  def ipv4_compat
    warn "IPAddr\##{__callee__} is obsolete", uplevel: 1 if $VERBOSE
    if !ipv4?
      raise InvalidAddressError, "not an IPv4 address: #{@addr}"
    end
-    return self.clone.set(@addr, Socket::AF_INET6)
+    clone = self.clone.set(@addr, Socket::AF_INET6)
+    clone.instance_variable_set(:@mask_addr, @mask_addr | 0xffffffffffffffffffffffff00000000)
+    clone
  end

ip4 = IPAddr.new('192.168.1.1').ipv4_compat
=> #<IPAddr: IPv6:0000:0000:0000:0000:0000:0000:c0a8:0101/ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff>
p [ip4.to_s, ip4.prefix]
["::192.168.1.1", 128]

ip4 = IPAddr.new('192.168.0.0/16').ipv4_compat
=> #<IPAddr: IPv6:0000:0000:0000:0000:0000:0000:c0a8:0000/ffff:ffff:ffff:ffff:ffff:ffff:ffff:0000>
p [ip4.to_s, ip4.prefix]
["::192.168.0.0", 112]

[taketo1113]

@ioquatix I create Pull Request (#86) to fix #ipv4_compat returning an invalid prefix.

[ioquatix]

Thanks everyone, appreciate your patience and contributions on this issue.