I've been trying to get in touch with the maintainers of the Binary
package, to report an issue. When I emailed the addresses given on
Hackage, I got an automated response saying I had used an address that
was no longer current.
I don't want to put pressure on anyone to fix my bug -- I didn't pay
anything for Binary, so it wouldn't be fair for me to have that kind of
expectation. At the same time, I don't really want my bug report to go
missing just because someone's email address has changed. Does anyone
know who I should be talking to? Or is there a bug tracker for the
Hackage packages somewhere?
I noticed this problem when I ran into some trouble with the network-dns
package. It would hang up as soon as I tried to send a query.
Eventually I traced the problem to the binary module, and reduced it to
this short test case:
module Main where
import qualified Data.Binary.Get as G
import qualified Data.ByteString.Lazy as B
main = do
urandom <- B.readFile "/dev/urandom"
let urandomParser :: G.Get [Int]
urandomParser = do
v <- G.getWord32be
rest <- urandomParser
return $ fromIntegral v : rest
seeds = G.runGet urandomParser urandom
print $ take 4 seeds
This code attempts to create an infinite list of random numbers -- a
technique also used by network-dns. It turns out that this code works
with binary-0.4.4 but not with binary-0.5.0.2. Both were built with
ghc-6.12.1 on Ubuntu. (I haven't tested with the intermediate versions
of the binary module.) It seems that with binary-0.5.0.2 there is some
unwanted strictness; something is evaluated for the whole list, even
though it is only the first few elements that are required.
Incidentally, if the test case is changed like this:
--- get_monad.hs 2010-05-28 11:31:02.399202535 +0100
+++ get_monad2.hs 2010-05-28 13:44:25.515486013 +0100
@@ -1,10 +1,12 @@
module Main where
+import Control.Monad
+
import qualified Data.Binary.Get as G
import qualified Data.ByteString.Lazy as B
main = do
- urandom <- B.readFile "/dev/urandom"
+ urandom <- liftM (B.take 64) $ B.readFile "/dev/urandom"
let urandomParser :: G.Get [Int]
urandomParser = do
v <- G.getWord32be
the program exits with an error:
get_monad2.hs: too few bytes. Failed reading at byte position 68
This seems to demonstrate that the program is reading more data than it
needs to.
Thanks,
Pete
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