Unix module API: nonblocking connect's errors retrieving

Unix module API: nonblocking connect's errors retrieving

[Vsevolod Fedorov]

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Hello, Camlers!

I have the following problem when using Unix module:

I issuing 'connect' for nonblocked-mode socket.
This can raise EINPROGRESS error meaning connect is not yet complete.
Then (as I taught by manuals) I use 'select' method and then 'getsockopt_int sock SO_ERROR' to retreive connect results.
The problem is: 'getsockopt_int' returns 'int' while I need Unix.error type.
I can't map int to error in good way.

Of couse, I can use some workarounds (and I had to use one), but they all are not look good.

May be is it the time to extend Unix module API?
For example, add function like 'getsockopt_error' or 'int_to_error'?

Seva


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Re: [Caml-list] Unix module API: nonblocking connect's errors retrieving

[Markus Mottl]

On 9/22/05, Vsevolod Fedorov <sevaAtWork@mail.ru> wrote:
> The problem is: 'getsockopt_int' returns 'int' while I need Unix.error type.
> I can't map int to error in good way.

I have also run into this same problem a while ago.

> May be is it the time to extend Unix module API?
> For example, add function like 'getsockopt_error' or 'int_to_error'?

There is already a C-function for handling that case in the
OCaml-runtime (unix_error).  You only need to write a C-wrapper that
converts the arguments to this function appropriately, and define an
"external"-function in OCaml.  Then you can raise the corresponding
Unix_error-exceptions by passing the error code and other arguments
(i.e. name of associated Unix-call and arguments).

But I agree, it would be a very good idea to expose this function in
the standard Unix-module (hint, hint!)...

Best regards,
Markus

--
Markus Mottl        http://www.ocaml.info        markus.mottl@gmail.com

Re: [Caml-list] Unix module API: nonblocking connect's errors retrieving

[Jerome Vouillon]

Hello,

On Thu, Sep 22, 2005 at 05:51:25PM +0400, Vsevolod Fedorov wrote:
> I have the following problem when using Unix module:
>
> I issuing 'connect' for nonblocked-mode socket.
> This can raise EINPROGRESS error meaning connect is not yet
> complete.  Then (as I taught by manuals) I use 'select' method and
> then 'getsockopt_int sock SO_ERROR' to retreive connect results.
> The problem is: 'getsockopt_int' returns 'int' while I need
> Unix.error type.  I can't map int to error in good way.
>
> Of couse, I can use some workarounds (and I had to use one), but
> they all are not look good.

I'm using the following piece of code as a work-around:

    begin try
      (* This succeeds only if the socket is connected *)
      ignore (Unix.getpeername fd)
    with Unix.Unix_error (Unix.ENOTCONN, _, _) ->
      (* This returns the right error message *)
      ignore (Unix.read fd " " 0 1))
    end

-- Jerome