[Haskell-cafe] Success and one last issue with Data.Binary
David Leimbach
leimy2k at gmail.com
Tue Jun 2 17:10:26 EDT 2009
On Tue, Jun 2, 2009 at 2:07 PM, David Leimbach <leimy2k at gmail.com> wrote:
>
>
> On Tue, Jun 2, 2009 at 1:56 PM, Thomas DuBuisson <
> thomas.dubuisson at gmail.com> wrote:
>
>> Again, I can't reproduce your problem. Are you getting data through
>> some previous Binary instance before calling the routines you show us
>> here?
>
>
> Ah good question... I'm calling "decode", but it's not clear that it's even
> running my instance of Get!!!!
>
> If I have a lazy bytestring, and call "decode", which instance of "Get"
> runs? Probably not my 9P message version I'll bet...
>
> geeze... :-(
>
AAAAANd... that was it. I totally didn't decode with the right decoder. By
the expression I had, it appears it was trying to decode a ByteString as a
String, and that was causing a big darned mess.
Thanks for all the help guys. I'm glad it's not a bug in the library, just
my dumb code
Dave
>
>
>
>> The code I tested with is below - I've tried it with both
>> 'getSpecific' paths by commenting out one path at a time. Both
>> methods work, shown below.
>>
>> Thomas
>>
>> *Main> decode test :: RV
>> Rversion {size = 19, mtype = 101, tag = 65535, msize = 1024, ssize =
>> 6, version = Chunk "9P2000" Empty}
>> *Main> :q
>> Leaving GHCi.
>> [... edit ...]
>> [1 of 1] Compiling Main ( p.hs, interpreted )
>> Ok, modules loaded: Main.
>> *Main> decode test :: RV
>> Rerror {size = 19, mtype = 101, tag = 65535, ssize = 1024, ename =
>> Chunk "\NUL\NUL\ACK\NUL9P2000" Empty}
>> *Main>
>>
>>
>>
>> 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}
>> | Rerror { size :: Word32,
>> mtype :: Word8,
>> tag :: Word16,
>> ssize :: Word16,
>> ename :: ByteString}
>> deriving (Eq, Ord, Show)
>>
>> instance Binary RV where
>> put = undefined
>> 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}
>> -}
>> = do t <- getWord16le
>> ss <- getWord16le
>> e <- getLazyByteString $ fromIntegral ss
>> return $ Rerror {size=s,
>> mtype=mt,
>> tag=t,
>> ssize=ss,
>> ename=e}
>>
>> test = pack
>> [ 0x13
>> , 0x00
>> , 0x00
>> , 0x00
>> , 0x65
>> , 0xff
>> , 0xff
>> , 0x00
>> , 0x04
>> , 0x00
>> , 0x00
>> , 0x06
>> , 0x00
>> , 0x39
>> , 0x50
>> , 0x32
>> , 0x30
>> , 0x30
>> , 0x30 ]
>>
>> On Tue, Jun 2, 2009 at 1:31 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
>> >
>> >
>> > _______________________________________________
>> > Haskell-Cafe mailing list
>> > Haskell-Cafe at haskell.org
>> > http://www.haskell.org/mailman/listinfo/haskell-cafe
>> >
>> >
>>
>
>
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