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#46 handling host-info errors
From: brownb@ja.gs.com (Robert E. Brown)
To: scsh-news@zurich.ai.mit.edu
Subject: handling host-info errors
Date: 07 Feb 2000 12:29:35 -0500
I'm using scsh-0.5.2 on Linux.
When my scsh script calls the function socket-connect
with a bad host name,
I get the following error
Error: name->host-info: non-zero herrno ~s ~s
1
#f
since socket-connect calls host-info, which calls name-
>host-info, which
indicates a problem by calling the error function.
I'd like to handle this condition and print a
reasonable error message that
the users of my script will understand. I want some
syntax like
with-errno-handler, but it should handle herror/host-
not-found. I have not
yet located what I need in the manual. Am I looking
in the wrong spot?
What syntax should I be using?
bob
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From: Eric Marsden <emarsden@mail.dotcom.fr>
To: scsh-news@zurich.ai.mit.edu
Subject: Re: handling host-info errors
Date: 07 Feb 2000 20:40:32 +0100
>>>>> "reb" == Robert E Brown <brownb@ja.gs.com> writes:
reb> I'd like to handle this condition and print a
reasonable error
reb> message that the users of my script will understand.
I want
reb> some syntax like with-errno-handler, but it should
handle
reb> herror/host-not-found.
I suppose that ideally there should be condition types
instead of raw
errors for many of these things, but there would be a huge
number of
them. Here is one way of intercepting specific error types:
#!/usr/local/bin/scsh \ -dm -m whnf -e main -s
!#
(define-structure whnf
(export main)
(open scheme scsh handle)
(begin
(define (with-host-not-found* thunk)
(call-with-current-continuation
(lambda (k)
(with-handler
(lambda (condition next)
(cond ((string-match "^name->host-info" (cadr
condition))
(display "No such host")
(newline)
(k))
(else (next))))
thunk))))
(define-syntax with-host-not-found
(syntax-rules ()
((with-host-not-found ?body ...)
(with-host-not-found* (lambda () ?body ...)))))
(define (main args)
(with-host-not-found
(host-info "foo.bar.com")))))
--
Eric Marsden
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user_id=27364
From: brownb@ja.gs.com (Robert E. Brown)
To: scsh-news@zurich.ai.mit.edu
Subject: Re: handling host-info errors
Date: 07 Feb 2000 17:51:14 -0500
I was afraid I'd have to do something like this.
One interesting thing I noticed is that the codes for host
info errors are
already defined and documented in scsh:
herror/host-not-found
herror/try-again
herror/no-recovery
herror/no-data
herror/no-address
I think it's fair for scsh routines to call "error" when
they're passed
illegal arguments. However, when I call socket-connect and
pass in a
perfectly reasonable host name string that DNS can't
resolve, I should get
an exception that's as easy to catch as the system call
errors I might get.
Thanks for your help!
bob
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