dmd: [PATCH] Improve socket connection errors handling.

dmd: [PATCH] Improve socket connection errors handling.

[Cyprien Nicolas]

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My first patch for dmd :-)

I thought about moving the interior format call to support.scm
(caught-error), but I wanted to keep the patch simple, and not making
two differents changes in one patch (error handling, support
improvements).

Comments welcome.
-- 
Cyprien/Fulax

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From 6e8f871198b661b631a319f3abaef71bc6269fb7 Mon Sep 17 00:00:00 2001
From: Cyprien Nicolas <cyp@fulax.fr>
Date: Thu, 10 Apr 2014 10:07:06 +0200
Subject: [PATCH] Improve socket connection errors handling.

If the user running `deco' does not have the rights privileges to open
the unix socket, the raised exception produces a backtrace.

* modules/dmd/comm.scm (open-connection): Add a (catch
  'system-error...) guard around the connect function call.
  The handler will abort the program in case of error.
---
 modules/dmd/comm.scm | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/modules/dmd/comm.scm b/modules/dmd/comm.scm
index d3743e6..4a0d383 100644
--- a/modules/dmd/comm.scm
+++ b/modules/dmd/comm.scm
@@ -63,7 +63,14 @@ return the socket."
   (with-fluids ((%default-port-encoding "UTF-8"))
     (let ((sock    (socket PF_UNIX SOCK_STREAM 0))
           (address (make-socket-address PF_UNIX file)))
-      (connect sock address)
+      (catch 'system-error
+        (lambda ()
+          (connect sock address))
+        (lambda (key . args)
+          (display (format #f "Error: Cannot connect to socket `~a': ~a\n"
+                           file (apply format #f (cadr args) (caddr args)))
+                   (current-error-port))
+          (quit 1)))
       sock)))
 
 (define (read-command port)
-- 
1.8.5.4


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Re: dmd: [PATCH] Improve socket connection errors handling.

[Ludovic Courtès]

Cyprien Nicolas <cyprien@nicolas.tf> skribis:

> My first patch for dmd :-)

Very cool, welcome!  :-)

Those backtraces had been bothering me for a while too, so thanks for
looking at it.

> From 6e8f871198b661b631a319f3abaef71bc6269fb7 Mon Sep 17 00:00:00 2001
> From: Cyprien Nicolas <cyp@fulax.fr>
> Date: Thu, 10 Apr 2014 10:07:06 +0200
> Subject: [PATCH] Improve socket connection errors handling.
>
> If the user running `deco' does not have the rights privileges to open
> the unix socket, the raised exception produces a backtrace.
>
> * modules/dmd/comm.scm (open-connection): Add a (catch
>   'system-error...) guard around the connect function call.
>   The handler will abort the program in case of error.

I pushed a couple of patches that achieve the same result slightly
differently: ‘open-connection’ is left unchanged and it’s the caller’s
responsibility to handle any errors; clients use the new
‘with-system-error-handling’ macro do handle all ‘system-error’
exceptions gracefully.

One remark:

> +        (lambda (key . args)
> +          (display (format #f "Error: Cannot connect to socket `~a': ~a\n"
> +                           file (apply format #f (cadr args) (caddr args)))
> +                   (current-error-port))

This could be directly (format (current-error-port) ...).

Also, we avoid uses of ‘car’, ‘cadr’ etc. in favor of ‘match’ (at least
in new code.)

Thanks!

Ludo’.

Re: dmd: [PATCH] Improve socket connection errors handling.

[Cyprien Nicolas]

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Il y a environ 24 minutes, Ludovic Courtès écrivit :
> I pushed a couple of patches that achieve the same result slightly
> differently: ‘open-connection’ is left unchanged and it’s the caller’s
> responsibility to handle any errors; clients use the new
> ‘with-system-error-handling’ macro do handle all ‘system-error’
> exceptions gracefully.

Right, much better and elegant fix :-)

> One remark:
>
> > +        (lambda (key . args)
> > +          (display (format #f "Error: Cannot connect to socket `~a': ~a\n"
> > +                           file (apply format #f (cadr args) (caddr args)))
> > +                   (current-error-port))
>
> This could be directly (format (current-error-port) ...).

I missed that part of the documentation.  Thanks for pointing
that out.

> Also, we avoid uses of ‘car’, ‘cadr’ etc. in favor of ‘match’ (at least
> in new code.)

Noted, thanks.

-- 
Cyprien/Fulax

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