Add parsing of shorthand IPv4 addresses (compatible with inet_aton)

Many applications (like browsers, curl, and wget) and even
Ruby's own Net::HTTP library accepts shorthand IPv4 addresses
like 127.1 or 2130706433 for 127.0.0.1.

It is confusing that IPAddr can't accept them.

CHANGELOG.md

@@ -1,3 +1,5 @@
+- Change IPv4 address parsing to recognize shorthand addresses, like [inet_aton](https://linux.die.net/man/3/inet_aton) does. [Feature #15734](https://bugs.ruby-lang.org/issues/15734)
+
 1.2.2
 -----
 

lib/ipaddr.rb

@@ -49,11 +49,17 @@ class IPAddr
   IN6FORMAT = (["%.4x"] * 8).join(':')
 
   # Regexp _internally_ used for parsing IPv4 address.
+  # Accepts shorthand forms like +inet_aton+ does:
+  #   127.0.0.1 = 127.1 = 0x7f.1 = 0177.1 =
+  #   192.168.255.255 = 192.168.65535 = 0xC0.0xA8FFFF = 3232301055
   RE_IPV4ADDRLIKE = %r{
-    \A
-    (\d+) \. (\d+) \. (\d+) \. (\d+)
-    \z
-  }x
+      \A
+      (?:((?:0x?)?[\da-f]{1,3})\.)?
+      (?:((?:0x?)?[\da-f]{1,3})\.)?
+      (?:((?:0x?)?[\da-f]{1,3})\.)?
+      (?:((?:0x?)?[\da-f]{1,10}))
+      \z
+    }xi
 
   # Regexp _internally_ used for parsing IPv6 address.
   RE_IPV6ADDRLIKE_FULL = %r{
@@ -617,11 +623,16 @@ def in_addr(addr)
       m = RE_IPV4ADDRLIKE.match(addr) or return nil
       octets = m.captures
     end
-    octets.inject(0) { |i, s|
-      (n = s.to_i) < 256 or raise InvalidAddressError, "invalid address"
-      s.match(/\A0./) and raise InvalidAddressError, "zero-filled number in IPv4 address is ambiguous"
-      i << 8 | n
-    }
+    octets.each.with_index.inject(0) do |address, (octet, index)|
+      address = address << 8
+      next address unless octet
+
+      n = Integer(octet)
+      max_exponent = index == 3 ? 8 * (1 + octets.count(&:nil?)) : 8
+      n < 2**max_exponent or raise InvalidAddressError, "invalid address"
+
+      address | n
+    end
   end
 
   def in6_addr(left)

test/test_ipaddr.rb

@@ -86,7 +86,6 @@ def test_s_new
     assert_equal("0:2:3:4:5:6:7:8", IPAddr.new("::2:3:4:5:6:7:8").to_s)
 
     assert_raise(IPAddr::InvalidAddressError) { IPAddr.new("192.168.0.256") }
-    assert_raise(IPAddr::InvalidAddressError) { IPAddr.new("192.168.0.011") }
     assert_raise(IPAddr::InvalidAddressError) { IPAddr.new("fe80::1%fxp0") }
     assert_raise(IPAddr::InvalidAddressError) { IPAddr.new("[192.168.1.2]/120") }
     assert_raise(IPAddr::InvalidAddressError) { IPAddr.new("[2001:200:300::]\nINVALID") }
@@ -99,6 +98,23 @@ def test_s_new
     assert_raise(IPAddr::AddressFamilyError) { IPAddr.new("::ffff:192.168.1.2/120", Socket::AF_INET) }
   end
 
+  def test_s_new_aton_compatible
+    assert_equal("127.0.0.1",       IPAddr.new("127.1").to_s)
+    assert_equal("127.0.0.2",       IPAddr.new("0x7F.2").to_s)
+    assert_equal("127.0.0.42",      IPAddr.new("0177.42").to_s)
+    assert_equal("127.0.0.34",      IPAddr.new("0x7f.042").to_s)
+    assert_equal("127.0.0.1",       IPAddr.new("2130706433").to_s)
+    assert_equal("255.255.255.255", IPAddr.new("4294967295").to_s)
+    assert_equal("192.168.1.1",     IPAddr.new("192.168.257").to_s)
+    assert_equal("10.1.136.148",    IPAddr.new("10.100500").to_s)
+    assert_equal("192.168.0.9",     IPAddr.new("192.168.0.011").to_s)
+    assert_equal("192.168.255.255", IPAddr.new("0xC0.0xA8FFFF").to_s)
+
+    assert_raise(IPAddr::InvalidAddressError) { IPAddr.new("192.168.0.256") }
+    assert_raise(IPAddr::InvalidAddressError) { IPAddr.new("256.168.0.1") }
+    assert_raise(IPAddr::InvalidAddressError) { IPAddr.new("4294967296") }
+  end
+
   def test_s_new_ntoh
     addr = ''
     IPAddr.new("1234:5678:9abc:def0:1234:5678:9abc:def0").hton.each_byte { |c|