[Haskell-cafe] Success and one last issue with Data.Binary

[David Leimbach]

On Tue, Jun 2, 2009 at 10:24 AM, Thomas DuBuisson <
thomas.dubuisson at gmail.com> wrote:

> > I think getRemainingLazyByteString expects at least one byte
> No, it works with an empty bytestring.  Or, my tests do with binary
> 0.5.0.1.
>
> The specific error means you are requiring more data than providing.


I've shown that I am not trying to decode more than I'm providing.  I've
asked, expliciitly, for 13 bytes, and then "remaining", and the library is
complaining about the 20th byte.



>
> First check the length of the bytestring you pass in to the to level
> decode (or 'get') routine and walk though that to figure out how much
> it should be consuming.  I notice you have a guard on the
> 'getSpecific' function, hopefully you're sure the case you gave us is
> the branch being taken.


The other branch is Rerror, which is a shorter message decode stream.
 Unfortunately, I can't get Debug.Trace to show anything to prove it's
taking this fork of the code.  I suppose I could unsafePerformIO :-)

Perhaps I just need a new version of "binary"??  I'll give it a go and try
your version.  But I need to decode over a dozen message types, so I will
need a case or guard or something.

Dave


>
> I think the issue isn't with the code provided.  I cleaned up the code
> (which did change behavior due to the guard and data declarations that
> weren't in the mailling) and it works fine all the way down to the
> expected minimum of 13 bytes.
>
>
> > import Data.ByteString.Lazy
> > import Data.Binary
> > import Data.Binary.Get
> >
> > data RV =
> > Rversion {     size   :: Word32,
> >                mtype  :: Word8,
> >                tag    :: Word16,
> >                msize  :: Word32,
> >                ssize  :: Word16,
> >                version :: ByteString}
> >       deriving (Eq, Ord, Show)
>
> > instance Binary RV where
> >  get = do s <- getWord32le
> >          mtype <- getWord8
> >          getSpecific s mtype
> >   where
> >    getSpecific s mt = do t <- getWord16le
> >                          ms <- getWord32le
> >                          ss <- getWord16le
> >                          v <- getRemainingLazyByteString
> >                          return $ Rversion {size=s,
> >                                             mtype=mt,
> >                                             tag=t,
> >                                             msize=ms,
> >                                             ssize=ss,
> >                                             version=v }
> >  put _ = undefined
>
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