como testar open-uri url existe antes de processar qualquer dado

Estou tentando processar o conteúdo de uma lista de links usando "open-uri" em ruby ​​(1.8.6), mas o ruim acontece quando recebo um erro quando um link está quebrado ou requer autenticação:

open-uri.rb:277:in `open_http': 404 Not Found (OpenURI::HTTPError)
from C:/tools/Ruby/lib/ruby/1.8/open-uri.rb:616:in `buffer_open'
from C:/tools/Ruby/lib/ruby/1.8/open-uri.rb:164:in `open_loop'
from C:/tools/Ruby/lib/ruby/1.8/open-uri.rb:162:in `catch' 

ou

C:/tools/Ruby/lib/ruby/1.8/net/http.rb:560:in `initialize': getaddrinfo: no address associated with hostname. (SocketError)
from C:/tools/Ruby/lib/ruby/1.8/net/http.rb:560:in `open'
from C:/tools/Ruby/lib/ruby/1.8/net/http.rb:560:in `connect'
from C:/tools/Ruby/lib/ruby/1.8/timeout.rb:53:in `timeout'

ou

C:/tools/Ruby/lib/ruby/1.8/net/protocol.rb:133:in `sysread': An existing connection was forcibly closed by the remote host. (Errno::ECONNRESET)
from C:/tools/Ruby/lib/ruby/1.8/net/protocol.rb:133:in `rbuf_fill'
from C:/tools/Ruby/lib/ruby/1.8/timeout.rb:62:in `timeout'
from C:/tools/Ruby/lib/ruby/1.8/timeout.rb:93:in `timeout'

existe uma maneira de testar a resposta (url) antes de processar qualquer dado?

o código é:

require 'open-uri'

smth.css.each do |item| 
 open('item[:name]', 'wb') do |file|
   file << open('item[:href]').read
 end
end

Muito obrigado