[Haskell-cafe] Success and one last issue with Data.Binary
John Van Enk
vanenkj at gmail.com
Tue Jun 2 16:36:43 EDT 2009
What happens if you use `getRemainingLazyByteString' in your error
branch instead of `getLazyByteString'?
On Tue, Jun 2, 2009 at 4:31 PM, David Leimbach <leimy2k at gmail.com> wrote:
>
>
> On Tue, Jun 2, 2009 at 1:28 PM, John Van Enk <vanenkj at gmail.com> wrote:
>>
>> I think Thomas' point was that some other branch in `getSpecific' is
>> running. Is there a chance we can see the rest of `getSpecific'?
>
> Sure: (In the meantime, I'll try the suggested code from before)
> get = do s <- getWord32le
> mtype <- getWord8
> getSpecific s mtype
> where
> getSpecific s mt
> | mt == mtRversion = do t <- getWord16le
> ms <- getWord32le
> ss <- getWord16le
> v <-
> getRemainingLazyByteString
> return $ MessageClient $
> Rversion {size=s,
>
> mtype=mt,
>
> tag=t,
>
> msize=ms,
>
> ssize=ss,
>
> version=v}
> | mt == mtRerror = do t <- getWord16le
> ss <- getWord16le
> e <- getLazyByteString $
> fromIntegral ss
> return $ MessageClient $ Rerror
> {size=s,
>
> mtype=mt,
>
> tag=t,
>
> ssize=ss,
>
> ename=e}
>
>>
>> On Tue, Jun 2, 2009 at 4:20 PM, David Leimbach <leimy2k at gmail.com> wrote:
>> > The thing is I have 19 bytes in the hex string I provided:
>> > 1300000065ffff000400000600395032303030
>> > That's 38 characters or 19 bytes.
>> > The last 4 are 9P2000
>> > 13000000 = 4 bytes for 32bit message payload, This is little endian
>> > for 19
>> > bytes total.
>> > 65 = 1 byte for message type. 65 is "Rversion" or the response type for
>> > a
>> > Tversion request
>> > ffff = 2 bytes for 16bit message "tag".
>> >
>> > 00040000 = 4 bytes for the 32 bit maximum message payload size I'm
>> > negotiating with the 9P server. This is little endian for 1024
>> > 0600 = 2 bytes for 16 bit value for the length of the "string" I'm
>> > sending.
>> > The strings are *NOT* null terminated in 9p, and this is little endian
>> > for
>> > 6 bytes remaining.
>> > 5032303030 = 6 bytes the ASCII or UTF-8 string "9P2000" which is 6 bytes
>> > 4 + 1 + 2 + 4 + 2 + 6 = 19 bytes.
>> > As far as I can see, my "get" code does NOT ask for a 20th byte, so why
>> > am I
>> > getting that error?
>> > get = do s <- getWord32le -- 4
>> > mtype <- getWord8 -- 1
>> > getSpecific s mtype
>> > where
>> > getSpecific s mt
>> > | mt == mtRversion = do t <- getWord16le -- 2
>> > ms <- getWord32le -- 4
>> > ss <- getWord16le -- 2
>> > v <-
>> > getRemainingLazyByteString -- remaining should be 6 bytes.
>> > return $ MessageClient $
>> > Rversion {size=s,
>> >
>> > mtype=mt,
>> >
>> > tag=t,
>> >
>> > msize=ms,
>> >
>> > ssize=ss,
>> >
>> > version=v}
>> > Should I file a bug? I don't believe I should be seeing an error
>> > message
>> > claiming a failure at the 20th byte when I've never asked for one.
>> > Dave
>> >
>> > On Tue, Jun 2, 2009 at 10:51 AM, John Van Enk <vanenkj at gmail.com> wrote:
>> >>
>> >> Thomas,
>> >>
>> >> You're correct. For some reason, I based my advice on the thought that
>> >> 19 was the minimum size instead of 13.
>> >>
>> >> On Tue, Jun 2, 2009 at 1:24 PM, 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.
>> >> > 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.
>> >> >
>> >> > 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
>> >> >
>> >>
>> >>
>> >>
>> >> --
>> >> /jve
>> >
>> >
>> > _______________________________________________
>> > Haskell-Cafe mailing list
>> > Haskell-Cafe at haskell.org
>> > http://www.haskell.org/mailman/listinfo/haskell-cafe
>> >
>> >
>>
>>
>>
>> --
>> /jve
>
>
--
/jve
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