Re: [Ocamlnet-devel] I am writing a NNTP client using Ocamlnet.

[GDWebster <gd...@wa...>]

> Thanks for putting together an NNTP client!  If you're interested, there
> was also some earlier prototyping of the NNTP protocol that is available
> in the CVS repository.  It is under the prototype directory.

Ah. No more this getting-excited-and-plowing-straight in stuff for me....

> You mention one of my main complaints I have with current POP interface --
> messages are read completely before returned to the client.  Initially,
> the object channel returned to the client would read data on demand.
> Unfortunately, if a client didn't read all of the data out of the channel,
> then the protocol would be in an inconsistent state.
>
> To avoid this, I added a quick fix to read the entire message before
> returning it.
>
> Here are the choices I see related to this issue:
>
>   - API has invariants that can't be checked by the compiler (e.g. it is
> an error to not cloes the channel before sending another command).  A
> custom in_obj_channel could be written that could fix the problem
> discussed above.

I think this is what I have done. This is Netnews' method for opening a 
channel to read a text response:

  method response_open_in () =
    if state <> `Command then raise Wrong_state (state, `Command);
    state <- `Receiving_text;
    let restore_state () = state <- `Command in
    new response_input_channel ic ~onclose:restore_state

All NNTP command methods have the "if state <> `Command then..." assertion. 
Improper flow control still causes a runtime error, but all at least it 
happens promptly and clearly this way, before anything really puzzling is 
allowed to happen.

"response_input_channel" objects read to the end of the current text response 
if they are closed before EOF, so there's no way to leave a response half 
read, but otherwise there is nothing special about them.

-- 
--
Glyn Webster ~ Simplicity Himself.