ntop: Measure address size in bytes

`IPAddr.ntop` takes the binary representation of an IP address, whose
length should be 4 or 16 *bytes* (not characters/codepoints).

The current implementation accepts strings in any encoding, but for
some values in non-BINARY encoding, it fails proper length check and
raises an `AddressFamilyError`. Since passing strings in a multibyte
encoding has never worked correctly for years, this patch makes it an
explicit error with an `InvalidAddressError`.

Fixes: #56

Author: hanazuki

lib/ipaddr.rb

@@ -110,8 +110,13 @@ def self.new_ntoh(addr)
 
   # Convert a network byte ordered string form of an IP address into
   # human readable form.
+  # It expects the string to be encoded in Encoding::US_ASCII (BINARY).
   def self.ntop(addr)
-    case addr.size
+    if addr.is_a?(String) && addr.encoding != Encoding::BINARY
+      raise InvalidAddressError, "invalid encoding (given #{addr.encoding}, expected BINARY)"
+    end
+
+    case addr.bytesize
     when 4
       addr.unpack('C4').join('.')
     when 16

test/test_ipaddr.rb

@@ -133,18 +133,37 @@ def test_s_new_ntoh
 
   def test_ntop
     # IPv4
-    assert_equal("192.168.1.1", IPAddr.ntop("\xC0\xA8\x01\x01"))
+    assert_equal("192.168.1.1", IPAddr.ntop("\xC0\xA8\x01\x01".b))
+    assert_equal("10.231.140.171", IPAddr.ntop("\x0A\xE7\x8C\xAB".b))
     # IPv6
     assert_equal("0000:0000:0000:0000:0000:0000:0000:0001",
-                 IPAddr.ntop("\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01"))
+                 IPAddr.ntop("\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01".b))
+    assert_equal("fe80:0000:0000:0000:f09f:9985:f09f:9986",
+                 IPAddr.ntop("\xFE\x80\x00\x00\x00\x00\x00\x00\xF0\x9F\x99\x85\xF0\x9F\x99\x86".b))
 
     # Invalid parameters
+    ## wrong length
     assert_raise(IPAddr::AddressFamilyError) {
-      IPAddr.ntop("192.168.1.1")
+      IPAddr.ntop("192.168.1.1".b)
     }
-
     assert_raise(IPAddr::AddressFamilyError) {
-      IPAddr.ntop("\xC0\xA8\x01\xFF1")
+      IPAddr.ntop("\xC0\xA8\x01\xFF1".b)
+    }
+    ## UTF-8
+    assert_raise(IPAddr::InvalidAddressError) {
+      IPAddr.ntop("192.168.1.1")
+    }
+    assert_raise(IPAddr::InvalidAddressError) {
+      IPAddr.ntop("\x0A\x0A\x0A\x0A")
+    }
+    assert_raise(IPAddr::InvalidAddressError) {
+      IPAddr.ntop("\x0A\xE7\x8C\xAB")
+    }
+    assert_raise(IPAddr::InvalidAddressError) {
+      IPAddr.ntop("\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01")
+    }
+    assert_raise(IPAddr::InvalidAddressError) {
+      IPAddr.ntop("\xFE\x80\x00\x00\x00\x00\x00\x00\xF0\x9F\x99\x85\xF0\x9F\x99\x86")
     }
   end