IPv4 octet parsing subject to Word overflow

[TravisCardwell]

The decodeIPv4TextReader function uses TextRead.decimal to parse Word values. Since Word is a bounded type, it is subject to overflow, which causes some invalid strings to parse successfully.

Example:

λ: import Net.IPv4 (decode)
λ: print $ decode "127.0.0.18446744073709551617"
Just (ipv4 127 0 0 1)

I do not think that this issue is significant, but I figure that I should at least report it.

[andrewthad]

If anyone wants to fix this, I would accept a PR for it.

EDIT: Also, thanks for reporting.

[TravisCardwell]

You are welcome!

I just submitted a PR with a fix.

[TravisCardwell]

I went for a hike this afternoon and realized that my comment about digitToInt was inaccurate. (It supports ASCII hex digits.) Checking the source to confirm, I realized that it is best to avoid both isDigit and digitToInt. This leads to slightly better performance: two fewer calls of fromIntegral, three fewer calls of ord, and one less subtraction per parsed character. I updated the pull request, squashing the commits to keep the commit history clean.

If you have any ideas for further improvement or other suggestions, please feel free to let me know, and I would be happy to look into them.

[andrewthad]

Resolved in #75

[TravisCardwell]

I realized that the readOctet function can be optimized further... All processed characters are guaranteed to be digits (~9) through use of Char.isDigit, so the range check in helper function go` is not necessary.

diff --git a/src/Net/IPv4.hs b/src/Net/IPv4.hs
index 40459d7..a020582 100644
--- a/src/Net/IPv4.hs
+++ b/src/Net/IPv4.hs
@@ -771,9 +771,8 @@ readOctet t = do
   where
   go :: Char -> (Int -> Maybe Int) -> Int -> Maybe Int
   go !d !f !n =
-    let d' = Char.ord d - 48
-        n' = n * 10 + d'
-    in  if d' >= 0 && d' <=9 && n' <= 255 then f n' else Nothing
+    let n' = n * 10 + Char.ord d - 48
+    in  if n' <= 255 then f n' else Nothing
 
 stripDecimal :: Text -> Either String Text
 stripDecimal t = case Text.uncons t of

Sorry for not noticing that before! If you would like to commit this optimization, I can create a PR.

[andrewthad]

Yeah, go ahead and PR. That would be great.