Sockets again

[Simon Marlow]

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=20
> The attached short program (compile with "ghc VServer.hs -o v=20
> -package net")
> is supposed to set up a server on port 15151, wait for a=20
> connection, read
> the first character from the connection, and print it out. =20
> Unfortunately
> if I test it, by running it, and starting up "telnet [machine] 15151"
> somewhere else, and then type some random text, EG=20
> "foo[RETURN]", it does
> not work.  It looks as if the problem is that VServer.hs issues the
> command
>     hSetBuffering handle (BlockBuffering (Just 4096))
> on the connection, because when I change it to
>     hSetBuffering handle NoBuffering
> the program works.
>=20
> However this is not what I want to do!!  Because setting=20
> NoBuffering on the
> handle is going to mean that when the Server *outputs*=20
> something, it will
> potentially be done very expensively character by character.  How do I
> get block buffering on the Server's output, but not have input to the
> server held up?

Hmm.  I rather think that hGetChar should always return a character
immediately if there is one available, regardless of the buffering mode.
Looking at the source, it appears that hGetLine behaves like this, as
does lazy reading with hGetContents.  I can't see any reason for waiting
for the buffer to be completely full before returning anything.

If you have a source tree handy, try the enclosed patch.  If not, make a
copy of hGetChar from the sources in libraries/base/GHC/IO.hs, apply the
patch, and compile it separately (you'll need to import GHC.Handle
explicitly, amongst other things).

Cheers,
	Simon

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