Re: [Haskell-beginners] Extract and integer from a ByteString

16 Jun 2010

      Tom Hobbs wrote:
...
I have a stream of bytes...
Where the first four bytes tell me the number of bytes I should read next in
order to get some string value...
What I have is code similar to the following;
readFromStream address port     =
               do
               h <- connectTo address (PortNumber port)
               hSetBuffering h NoBuffering
               L.hPut h (encode (0xFAB10000 :: Word32))
               p <- L.hGet h 4
               readData h (extractInt((L.unpack p)))
extractInt      = foldl addDigit 0
               where
               addDigit num d = 10*num + d
readData h c    = do
               print c
               s <- L.hGet h c
               print s
You're looking for the binary package. That is a general
library for encoding and decoding of binary data streams
via lazy bytestrings.

http://hackage.haskell.org/package/binary

Then you can write:

import Data.Binary.Get
...
    n <- fmap (runGet word32be) $ L.hGet h 4
    theString <- L.hGet h n

This gives you theString as a lazy bytestring, of course.
You take it from there.

Regards,
Yitz

Re: [Haskell-beginners] Extract and integer from a ByteString

Yitzchak Gale