Asp Forum - rescue doesn't handle every error

Mage

2/23/2007 8:11:00 AM

Hello,

the example works both on Debian, Ruby 1.8.4 and Gentoo, Ruby 1.8.5
-----------------------------------

irb(main):006:0> require 'open-uri'
=> true
irb(main):007:0> begin
irb(main):008:1* open('http://www.url.with.timeout.p...).read
irb(main):009:1> rescue
irb(main):010:1> puts 'timeout'
irb(main):011:1> end
/usr/lib/ruby/1.8/timeout.rb:54:in `rbuf_fill': execution expired
(Timeout::Error)
from /usr/lib/ruby/1.8/timeout.rb:56:in `timeout'
from /usr/lib/ruby/1.8/timeout.rb:76:in `timeout'
from /usr/lib/ruby/1.8/net/protocol.rb:132:in `rbuf_fill'
from /usr/lib/ruby/1.8/net/protocol.rb:116:in `readuntil'
from /usr/lib/ruby/1.8/net/protocol.rb:126:in `readline'
from /usr/lib/ruby/1.8/net/http.rb:2224:in `read_chunked'
from /usr/lib/ruby/1.8/net/http.rb:2204:in `read_body_0'
from /usr/lib/ruby/1.8/net/http.rb:2170:in `read_body'
... 13 levels...
from /usr/lib/ruby/1.8/open-uri.rb:30:in `open'
from (irb):8:in `irb_binding'
from /usr/lib/ruby/1.8/irb/workspace.rb:52:in `irb_binding'
from /usr/lib/ruby/1.8/irb/workspace.rb:52

------------------------------------------

I think it's terrible bad. Rescue without explicit error type should
have deal with *every* error. Its purpose is to handle unexpected
errors. My production application stopped working by a bad url, but the
whole process was inside a begin-rescue-end block.

This is not the first time. I have seen same when I was dealing with
SCGI source code.

Correct me if I am wrong but I think this is a serious issue in Ruby's
error handling and should be fixed soon.

Mage

9 Answers

Peña, Botp

2/23/2007 8:23:00 AM

From: Mage [mailto:mage@mage.hu] :
# irb(main):006:0> require 'open-uri'
# => true
# irb(main):007:0> begin
# irb(main):008:1* open('http://www.url.with.timeout.p...).read
# irb(main):009:1> rescue

rescue Exception

# irb(main):010:1> puts 'timeout'
# irb(main):011:1> end

kind regards -botp

Robert Klemme

2/23/2007 8:26:00 AM

rescue without exception spec just handles RuntimeError - that's also
documented behavior IIRC.

Regards

robert

Mage

2/23/2007 8:33:00 AM

PeÃ±a wrote:
> rescue Exception
>
Thank you, it works.

I googled for string "rescue exception", and I found this: "'rescue' by
itself is like 'rescue StandardError', I believe (which catches
StandardError and all its subclasses)".

If it works that way, I think, it should be documented in the Ruby book,
exception part.

Have a nice day.

Mage

Mage

2/23/2007 8:35:00 AM

Robert Klemme wrote:
>
> rescue without exception spec just handles RuntimeError - that's also
> documented behavior IIRC.
>
I think it's not documented, or I just skipped?

http://www.rubycentral.com/book/tut_excep...

Mage

come

2/23/2007 8:49:00 AM

There is a timeout package in the standard library which will raise an
exception. You could use it in your code like this :

require "timeout"
require "open-uri"

begin
Timeout::timeout(60) do |timeout_length|
open('http://www.url.with.timeout.p...).read
end
rescue Timeout::Error
puts "timeout : 60 seconds"
end

On 23 f?v, 09:11, Mage <m...@mage.hu> wrote:
> Hello,
>
> the example works both on Debian, Ruby 1.8.4 and Gentoo, Ruby 1.8.5
> -----------------------------------
>
> irb(main):006:0> require 'open-uri'
> => true
> irb(main):007:0> begin
> irb(main):008:1* open('http://www.url.with.timeout.p...).read
> irb(main):009:1> rescue
> irb(main):010:1> puts 'timeout'
> irb(main):011:1> end
> /usr/lib/ruby/1.8/timeout.rb:54:in `rbuf_fill': execution expired
> (Timeout::Error)
> from /usr/lib/ruby/1.8/timeout.rb:56:in `timeout'
> from /usr/lib/ruby/1.8/timeout.rb:76:in `timeout'
> from /usr/lib/ruby/1.8/net/protocol.rb:132:in `rbuf_fill'
> from /usr/lib/ruby/1.8/net/protocol.rb:116:in `readuntil'
> from /usr/lib/ruby/1.8/net/protocol.rb:126:in `readline'
> from /usr/lib/ruby/1.8/net/http.rb:2224:in `read_chunked'
> from /usr/lib/ruby/1.8/net/http.rb:2204:in `read_body_0'
> from /usr/lib/ruby/1.8/net/http.rb:2170:in `read_body'
> ... 13 levels...
> from /usr/lib/ruby/1.8/open-uri.rb:30:in `open'
> from (irb):8:in `irb_binding'
> from /usr/lib/ruby/1.8/irb/workspace.rb:52:in `irb_binding'
> from /usr/lib/ruby/1.8/irb/workspace.rb:52
>
> ------------------------------------------
>
> I think it's terrible bad. Rescue without explicit error type should
> have deal with *every* error. Its purpose is to handle unexpected
> errors. My production application stopped working by a bad url, but the
> whole process was inside a begin-rescue-end block.
>
> This is not the first time. I have seen same when I was dealing with
> SCGI source code.
>
> Correct me if I am wrong but I think this is a serious issue in Ruby's
> error handling and should be fixed soon.
>
> Mage

Ben Bleything

2/23/2007 9:30:00 AM

On Fri, Feb 23, 2007, Mage wrote:
> Robert Klemme wrote:
> > rescue without exception spec just handles RuntimeError - that's also
> > documented behavior IIRC.
> >
> I think it's not documented, or I just skipped?
>
> http://www.rubycentral.com/book/tut_excep...

It is:

The match is made using $!.kind_of?(parameter), and so will succeed if
the parameter has the same class as the exception or is an ancestor of
the exception. If you write a rescue clause with no parameter list, the
parameter defaults to StandardError.

Easy to miss, though. Took me a while to find it. The explanation is
clearer (IIRC) in the second edition.

Ben

Brian Candler

2/23/2007 10:47:00 AM

On Fri, Feb 23, 2007 at 05:34:53PM +0900, Mage wrote:
> Robert Klemme wrote:
> >
> > rescue without exception spec just handles RuntimeError - that's also
> > documented behavior IIRC.
> >
> I think it's not documented, or I just skipped?
>
> http://www.rubycentral.com/book/tut_excep...

which does say:

"If you write a rescue clause with no parameter list, the parameter defaults
to StandardError."

Mage

2/23/2007 3:09:00 PM

Brian Candler wrote:
>
>> I think it's not documented, or I just skipped?
>>
>> http://www.rubycentral.com/book/tut_excep...
>>
>
> which does say:
>
> "If you write a rescue clause with no parameter list, the parameter defaults
> to StandardError."
>
>
You are right, it's my mistake.

Mage

Jano Svitok

2/23/2007 3:18:00 PM

On 2/23/07, Mage <mage@mage.hu> wrote:
> Brian Candler wrote:
> >
> >> I think it's not documented, or I just skipped?
> >>
> >> http://www.rubycentral.com/book/tut_excep...
> >>
> >
> > which does say:
> >
> > "If you write a rescue clause with no parameter list, the parameter defaults
> > to StandardError."
> >
> >
> You are right, it's my mistake.

This is a pretty common mistake, so maybe in the next edition it
should be somehow highlighted. Maybe a separate paragraph or
something...

comp.lang.ruby

rescue doesn't handle every error

Mage

Peña, Botp

Robert Klemme

Mage

Mage

come

Ben Bleything

Brian Candler

Mage

Jano Svitok

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