`readlong': undefined method `unpack' for nil:NilClass (NoMethodError)

[kyanny]

EXIFR::TIFF::Data#readlong throws exception for this image file.

http://dl.dropbox.com/u/4289117/2011-01-02%2016.24.57%5B1%5D.jpg

This photo was taken by Galaxy S camera in consinuous shooting mode.

backtrace is below.

$ exifr ~/daniel.jpg 
/usr/lib64/ruby/gems/1.8/gems/exifr-1.0.5/lib/exifr/tiff.rb:573:in `readlong': undefined method `unpack' for nil:NilClass (NoMethodError)
        from /usr/lib64/ruby/gems/1.8/gems/exifr-1.0.5/lib/exifr/tiff.rb:460:in `initialize'
        from /usr/lib64/ruby/gems/1.8/gems/exifr-1.0.5/lib/exifr/tiff.rb:399:in `new'
        from /usr/lib64/ruby/gems/1.8/gems/exifr-1.0.5/lib/exifr/tiff.rb:399:in `initialize'
        from /usr/lib64/ruby/gems/1.8/gems/exifr-1.0.5/lib/exifr/tiff.rb:398:in `times'
        from /usr/lib64/ruby/gems/1.8/gems/exifr-1.0.5/lib/exifr/tiff.rb:398:in `initialize'
        from /usr/lib64/ruby/gems/1.8/gems/exifr-1.0.5/lib/exifr/tiff.rb:448:in `new'
        from /usr/lib64/ruby/gems/1.8/gems/exifr-1.0.5/lib/exifr/tiff.rb:448:in `add_field'
        from /usr/lib64/ruby/gems/1.8/gems/exifr-1.0.5/lib/exifr/tiff.rb:399:in `initialize'
         ... 14 levels...
        from /usr/lib64/ruby/gems/1.8/gems/exifr-1.0.5/bin/exifr:50:in `each'
        from /usr/lib64/ruby/gems/1.8/gems/exifr-1.0.5/bin/exifr:50
        from /usr/bin/exifr:19:in `load'
        from /usr/bin/exifr:19

readlong (and also readshort) try to access data out of range.
self[pos..(pos + 3)] returns nil, so nil.unpack called and NoMethodError thrown.

https://github.com/remvee/exifr/blob/master/lib/exifr/tiff.rb#L572

In my case, I wrote wrapper method and catched all exception from readlong.

https://gist.github.com/1096796

I'm using rails, so I put these code in config/environment.rb.

my envrionment: ruby version 1.8.6, exifr version 1.0.5 (newest)

[kyanny]

Very quick fix, thanks!