Ruby URL.parse error - ruby

Question

Here is my ruby program
require 'net/http'
require 'uri'
begin
url = URI.parse("http://google.com")
rescue Exception => err
p err
exit
end
http = Net::HTTP.new(url.host, url.port)
res = http.head("/")
p res.code
It works fine, however if I remove http:// from URL.parse(), It gives me this error:
/usr/lib/ruby/1.9.1/net/http.rb:1196:in `addr_port': undefined method `+' for nil:NilClass (NoMethodError) ...
from /usr/lib/ruby/1.9.1/net/http.rb:1094:in `request'
from /usr/lib/ruby/1.9.1/net/http.rb:860:in `head'
Is it the correct way to handle Exception ?
I know maybe the URL is not correct, but It should raise an exception URI::InvalidURIError instead of accepting and continue the program ?

Answer 1

If you say u = URI.parse('http://google.com'), you'll get a URI::HTTP back and the u.port will have a default of 80. If you say u = URI.parse('google.com'), you'll get a URI::Generic back with the u.port will be nil as will u.host.
So, when you do this:
url = URI.parse('google.com')
http = Net::HTTP.new(url.host, url.port)
You're really doing this:
http = Net::HTTP.new(nil, nil)
and Net::HTTP doesn't like that very much at all. You could try something like this instead:
if(str.to_s.empty?)
# complain loudly about a missing str
end
begin
url = URI.parse(str)
url = URI.parse('http://' + str) if !url.scheme
if(url.scheme != 'http' && url.scheme != 'https')
# more complaining about bad input
end
http = Net::HTTP.new(url.host, url.port)
#...
rescue URI::Error => e
# even yet more complaining
end
That sort of thing should bypass the exception completely and cover a few other things that you might be interested in.

Answer 2

You have to specifically catch URI::InvalidURIError, as it is not a descendant of Exception. See:
irb(main):002:0> URI::InvalidURIError.is_a?(Exception)
=> false
So the fix for your code would be:
begin
url = URI.parse("http://google.com")
rescue URI::InvalidURIError => err
p err
exit
end

Answer 3

The correct way is not to let any exception happen at all, but to check your conditions beforehand. Like this:
require 'net/http'
require 'uri'
begin
url = URI.parse("http://google.com")
rescue URI::InvalidURIError => err
p err
exit
end
if url.host && url.port
http = Net::HTTP.new(url.host, url.port)
res = http.head("/")
p res.code
else
p 'Error parsing url'
end