Fwd: [Haskell-cafe] fine control of bytestring streaming

Alberto G. Corona agocorona at gmail.com
Wed Jul 28 16:04:09 EDT 2010

Thanks  Henning ,

I finally found the problem and an elegant solution (I guess)

The problem is not, as I feared, the coalescence of bytestring chunks
in more bigger chunks, but the buffering mode of the stream.  The
stream simply waits until the buffer is full to stream its content.

So the solution is either to change the blocking to NoBlocking (with
hSetBuffering, and very inefficient) or else to modify
Data.BytreString.Lazy.hPut  to insert an hFlush after each chunk
delivered to the stream:

import qualified Data.ByteString as S(hPut)
import  Data.ByteString.Lazy.Internal(foldrChunks)

   myhPut :: Handle →  ByteString →  IO ()
   myhPut h cs = foldrChunks (λc rest →  S.hPut h c >>
System.IO.hFlush h >> rest) (return ()) cs

the original Data.BytreString.Lazy.hPut  has not the hFlush step.

I had to modify simpleServer to do that and now I control exactly the
size of the fragment and the moment when it is delivered, because  the
mappend instance of ByteString.Lazy respect the chunks created with
"pack (String)".

I give it to the consideration of the maintainers of
Data.ByteString.Lazy (Dons),, because lazy bytestrings, since are a
concatenation of user made blocks,  have such possibility of
controlling precise streaming. Something that neither ordinary strings
nor strict bytestring, and I guess nothing else has. Don´t miss out

2010/7/27, Henning Thielemann <lemming at henning-thielemann.de>:
> On Tue, 27 Jul 2010, Alberto G. Corona wrote:
>> The question is:  are there some way to control bytestring streaming?.
>> Can It be done without the stream handler?
> I think there is a function that converts a lazy ByteString to a list of
> strict ByteStrings, that should work without copying the chunk data
> around. On this chunk list you can do all kind of manipulations, like
> merging adjacent small chunks.
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