# streamly-bytestring

Library for streamly and bytestring interoperation.

If you are writing code from scratch, please use `Streamly.Data.Array.Foreign`
which is a generalization of `ByteString` and better integrated with streamly.

This library is to enable interoperation of streamly with existing code that
uses `ByteString`.

The package provides APIs to interconvert between strict `Bytestring` and
streamly `Array Word8` and between lazy `Bytestring` and stream of `Array
Word8`.

The interconversion in the case of strict `Bytestring` and streamly `Array
Word8` has no overhead as the underlying representation of ByteString and Array
are the same, we just need to rewrap the data in a different type.

## Usage

This is a dumb program that counts the number of bytes in a file.

```
import qualified Streamly.Prelude as S

import qualified Data.ByteString as BS
import qualified Data.ByteString.Lazy as BSL

import qualified Streamly.External.ByteString as Strict
import qualified Streamly.External.ByteString.Lazy as Lazy

import System.IO (FilePath)

strictByteStringSize :: BS.ByteString -> IO Int
strictByteStringSize bs = S.length $ S.unfold Strict.read bs

lazyByteStringSize :: BSL.ByteString -> IO Int
lazyByteStringSize bsl = S.foldl' (+) 0
                         $ S.mapM strictByteStringSize
                         $ S.map Strict.fromArray
                         $ Lazy.toChunks bsl

fileSize :: FilePath -> IO Int
fileSize path = do
    bsl <- BSL.readFile path
    lazyByteStringSize bsl
```