From: brian ford <brixen@...>
Date: 2011-09-01T04:03:37+09:00
Subject: [ruby-core:39215] Re: [Ruby 1.9 - Bug #5237] IO.copy_stream calls #read on an object infinitely many times

Hi,

On Tue, Aug 30, 2011 at 8:48 PM, Motohiro KOSAKI
<kosaki.motohiro@gmail.com> wrote:
>
> Issue #5237 has been updated by Motohiro KOSAKI.
>
>
> If you are reading following paragraph,
>
>> * �At end of file, it returns <code>nil</code> or <code>""</code>
>> * �depend on <i>length</i>.
>> * �<code><i>ios</i>.read()</code> and
>> * �<code><i>ios</i>.read(nil)</code> returns <code>""</code>.
>> * �<code><i>ios</i>.read(<i>positive-integer</i>)</code> returns <code>nil</code>.
>
> you have to read following paragraph too, I think.
>
>> * �If <i>length</i> is a positive integer,
>> * �it try to read <i>length</i> bytes without any conversion (binary mode).
>> * �It returns <code>nil</code> or a string whose length is 1 to <i>length</i> bytes.
>> * �<code>nil</code> means it met EOF at beginning.
>
> *AT BEGINNING*
>
> Thus, positive length destination buffer and returning nil are exclusive. Now, I don't think
> we need doc fix.
>
> but I'm not talking about a behavior change. I have no strong opinion. It's another story. I'm waiting akr-san's response.

I'm not following your explanation. The return value, whether nil or
anything else, including an empty string or any string (one byte or
not) will NOT cause the copy_stream method to return. It will loop
infinitely unless the buffer that is passed in is set to "". In fact,
I can return *anything* from #read as long as I set the buffer to "".
This is bizarre.

At the least, the rdoc should note that to participate in this API,
#read must set the buffer to "" to signal EOF. Still, in my opinion,
that is a bad API. The return value should be the sole way to signal
EOF given that the arguments to #read are optional.

sasha:rubinius2.0 brian$ cat copy_stream_bug.rb
class A
  def initialize
    @count = 0
    @read = 0
  end

  def read(bytes, buffer)
    puts buffer
    puts "read: #{@count += 1}"
    @read += 1
    case @read
    when 1
      buffer.replace "this is"
    when 2
      buffer << " a test"
    else
      buffer.replace ""
      return A.new
    end
  end
end

a = A.new
IO.copy_stream a, "copy_stream_test"
sasha:rubinius2.0 brian$ ruby -v copy_stream_bug.rb
ruby 1.9.2p290 (2011-07-09 revision 32553) [x86_64-darwin10.8.0]

read: 1
this is
read: 2
this is a test
read: 3


Thanks,
Brian