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Compress the longest run of zero fields in IPv6#to_s #160

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Compress the longest run of zero fields in IPv6#to_s #160

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26 changes: 25 additions & 1 deletion lib/resolv.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -3347,7 +3347,31 @@ def initialize(address) # :nodoc:
attr_reader :address

def to_s # :nodoc:
sprintf("%x:%x:%x:%x:%x:%x:%x:%x", *@address.unpack("nnnnnnnn")).sub(/(^|:)0(:0)+(:|$)/, '::')
words = @address.unpack("nnnnnnnn")

# RFC 5952 Section 4.2.3: compress the longest run of two or more
# zero fields, choosing the first one when runs are equally long.
best_start = best_len = nil
i = 0
while i < 8
if words[i] == 0
j = i
j += 1 while j < 8 && words[j] == 0
if j - i >= 2 && (best_len.nil? || j - i > best_len)
best_start, best_len = i, j - i
end
i = j
else
i += 1
end
end

hex = words.map {|word| sprintf("%x", word) }
return hex.join(":") unless best_start

head = hex[0, best_start].join(":")
tail = hex[(best_start + best_len)..-1].join(":")
"#{head}::#{tail}"
end

def inspect # :nodoc:
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6 changes: 5 additions & 1 deletion test/resolv/test_dns.rb
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Expand Up @@ -622,8 +622,12 @@ def test_ipv6_to_s
["2001::", "2001::0"],
["2001:db8:0:1:1:1:1:1", "2001:db8:0:1:1:1:1:1"], # RFC 5952 Section 4.2.2.
["2001:db8::1:1:1:1", "2001:db8:0:0:1:1:1:1"],
["1::1:0:0:0:1", "1:0:0:1:0:0:0:1"],
["1:0:0:1::1", "1:0:0:1:0:0:0:1"], # RFC 5952 Section 4.2.3.
["1::1:0:0:1", "1:0:0:0:1:0:0:1"],
["2001:db8::1:0:0:1", "2001:db8:0:0:1:0:0:1"], # RFC 5952 Section 4.2.3.
["2001:0:0:1::", "2001:0:0:1:0:0:0:0"],
["::1:0:0:1", "0:0:0:0:1:0:0:1"],
["1:2:3:4:5:6:7:8", "1:2:3:4:5:6:7:8"],
]

test_cases.each do |expected, ipv6|
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