require 'rubygems'
require 'uri'
require 'mechanize'
require 'rack/utils'

# so you can do `params.inspect` throughout Mechanize
class NilClass; def search(*args); []; end; end

Mechanize::Chain::PostConnectHook.class_eval do

def handle(ctx, params)
headers = params[:response].to_hash
if headers.has_key?("location")
headers["location"].each do |location|
url = URI.parse(location)
if url.host == "localhost" && url.port == 4567
params[:res_klass] = Net::HTTPSuccess
end
end
end

p params.keys
#=> [:res_klass, :uri, :response_body, :referer, :response, :agent, :verb, :redirects, :connection, :params, :request, :headers]
p params[:uri]
#=> #
p params[:response]
#=> #
p params[:response].to_hash
#=> {"location"=>["http://somesite.com"], "expires"=>["Sat, 01 Jan 2000 00:00:00 GMT"], "content-type"=>["text/html; charset=utf-8"], "date"=>["Mon, 16 Aug 2010 04:31:13 GMT"], "content-length"=>["0"], "cache-control"=>["private, no-cache, no-store, must-revalidate"], "x-cnection"=>["close"], "pragma"=>["no-cache"]}

super(ctx, params)
end

end

agent = Mechanize.new
page = agent.get("https://somesite.com")
# ... tons of redirects,
# then finally we find a match in our `handle` method above,
# and reset the `params[:res_klass]` to `Net::HTTPSuccess`.
# that is a hack to say basically,
# "return the page, we found what we want"
location = URI.parse(page.response.to_hash["location"].to_a.first)
params = Rack::Utils.parse_query(location.query)

Read more: http://feeds.dzone.com/~r/dzone/snippets/~3/ea3z8Lo2Ppk/12075