Re: [Ocaml-lib-devel] IO.really_nread

[Bardur A. <oca...@sc...>]

On Mon, Aug 30, 2004 at 10:35:51PM +0200, Nicolas Cannasse wrote:

> > Hi all,
> > 
> > It seems there is no function to read exactly n characters
> > into a string (ie. IO.nread just without automatically
> > shortening the string if EOF is hit while reading). Since
> > at least one person needs it (me :)) I thought I would add
> > this:
> > 
> >    let really_nread i n =
> >         if n < 0 then raise (Invalid_argument "IO.really_nread");
> >         if n = 0 then
> >                 ""
> >         else
> >         let s = String.create n in
> >         let l = ref n in
> >         let p = ref 0 in
> >         while !l > 0 do
> >                 let r = i.in_input s !p !l in
> >                 p := !p + r;
> >                 l := !l - r;
> >         done;
> >         s
> > 
> > which is exactly the same code as IO.nread, except it
> > doesn't try to catch the No_more_input exception.
> > 
> > Any objections to adding this?
> 
> This will cause an infinite loop on non-blocking IO (r = 0).
> You might want to raise Sys_blocked_io in this case.
> 

Hmm... the channel adapter uses Pervasives.input to read.
This in turn uses Pervasives.unsafe_input, which uses
caml_ml_input(), which uses caml_do_read() which will
actually raise Sys_blocked_io itself when the read()
function returns the appropriate error code. So unless I'm
missing something it should actually work correctly for
non-blocking IO...

-- 
Bardur Arantsson
<ba...@im...>
<ba...@sc...>

Hard work often pays off after time. But laziness always pays off
now.
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