From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <till.varoquaux@gmail.com>
X-Spam-Checker-Version: SpamAssassin 3.1.3 (2006-06-01) on yquem.inria.fr
X-Spam-Level: *
X-Spam-Status: No, score=1.1 required=5.0 tests=AWL,SPF_NEUTRAL 
	autolearn=disabled version=3.1.3
Received: from concorde.inria.fr (concorde.inria.fr [192.93.2.39])
	by yquem.inria.fr (Postfix) with ESMTP id 0BB0BBC0A
	for <caml-list@yquem.inria.fr>; Wed, 10 Jan 2007 18:08:59 +0100 (CET)
Received: from nf-out-0910.google.com (nf-out-0910.google.com [64.233.182.187])
	by concorde.inria.fr (8.13.6/8.13.6) with ESMTP id l0AH8w8Z025072
	for <caml-list@inria.fr>; Wed, 10 Jan 2007 18:08:58 +0100
Received: by nf-out-0910.google.com with SMTP id m19so550241nfc
        for <caml-list@inria.fr>; Wed, 10 Jan 2007 09:08:58 -0800 (PST)
DomainKey-Signature: a=rsa-sha1; c=nofws;
        d=gmail.com; s=beta;
        h=received:message-id:date:from:to:subject:mime-version:content-type:content-transfer-encoding:content-disposition;
        b=qntdUI1LpOEBT6uwqMX5/on3AqVyGc8B/NRGTut69fgUeb5+A+15HH/5bBBIHYbiERaCA6oUOK0PCfyXPeMmzNqDJs8Pn81WQZpYKOFVbwBja5QFZEGTMJS6n3qQQrN/Hlm0adXuWmNqIqddJM0+zWqXw0YS0o/r5OpSx7U+ASk=
Received: by 10.82.184.2 with SMTP id h2mr112316buf.1168448938257;
        Wed, 10 Jan 2007 09:08:58 -0800 (PST)
Received: by 10.82.152.3 with HTTP; Wed, 10 Jan 2007 09:08:57 -0800 (PST)
Message-ID: <9d3ec8300701100908m40f986dmafd9c41cb9fe06ba@mail.gmail.com>
Date: Wed, 10 Jan 2007 18:08:57 +0100
From: "Till Varoquaux" <till.varoquaux@gmail.com>
To: "ocaml ml" <caml-list@inria.fr>
Subject: Implementing rollback channels with Ocamlnet
MIME-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Content-Disposition: inline
X-j-chkmail-Score: MSGID : 45A51DAA.000 on concorde : j-chkmail score : X : 0/20 1 0.000 -> 1
X-Miltered: at concorde with ID 45A51DAA.000 by Joe's j-chkmail (http://j-chkmail . ensmp . fr)!
X-Spam: no; 0.00; ocamlnet:01 buffered:01 netstream:01 netchannels:01 val:01 mutable:01 val:01 mutable:01 netbuffer:01 blit:01 netchannels:01 rec:01 rec:01 exception:01 len:02 

I need to be able to backtrack while reading a stream. The way I tried
to do it was to build a new in_channel reading from the window of the
previous (buffered) channel.
Here's my current failed attempt:

open Netstream;;

exception BaseChannelAccess

class rollback_chan (is:in_obj_stream) : Netchannels.rec_in_channel=
object
 val mutable p_in=is#pos_in
 val mutable closed=false
 method close_in  () = ()
  method input dest dest_pos len =
  if (is#pos_in != p_in) then
   raise BaseChannelAccess;
  is#want(p_in+len);
  Netbuffer.blit is#window p_in dest dest_pos len;
  p_in <- p_in + len;
  len
end;;

let rollback_chan input=
  Netchannels.lift_in(`Rec (new rollback_chan(input)))

It doesn't work (at all). I must be getting something awfully wrong,
has anyone had more chance trying something similar?

Till