使用OpenUri，我如何获取重定向页面的内容？

Question

I want to get data from this page:

http://www.canadapost.ca/cpotools/apps/track/personal/findByTrackNumber?trackingNumber=0656887000494793

But that page forwards to:

http://www.canadapost.ca/cpotools/apps/track/personal/findByTrackNumber?execution=eXs1

So, when I use open , from OpenUri, to try and fetch the data, it throws a RuntimeError error saying HTTP redirection loop:

I'm not really sure how to get that data after it redirects and throws that error.

Answer 1

You need a tool like Mechanize . From it's description:

The Mechanize library is used for automating interaction with websites. Mechanize automatically stores and sends cookies, follows redirects, can follow links, and submit forms. Form fields can be populated and submitted. Mechanize also keeps track of the sites that you have visited as a history.

which is exactly what you need. So,

sudo gem install mechanize

then

require 'mechanize'
agent = WWW::Mechanize.new
page = agent.get "http://www.canadapost.ca/cpotools/apps/track/personal/findByTrackNumber trackingNumber=0656887000494793"

page.content # Get the resulting page as a string
page.body # Get the body content of the resulting page as a string
page.search(".somecss") # Search for specific elements by XPath/CSS using nokogiri

and you're ready to rock 'n' roll.

Answer 2

While mechanize is a wonderful tool I prefer to "cook" my own thing.

If you are serious about parsing you can take a look at this code. It serves to crawl thousands of site on an international level everyday and as far as I have researched and tweaked there isn't a more stable approach to this that also allows you to highly customize later on your needs.

require "open-uri"
require "zlib"
require "nokogiri"
require "sanitize"
require "htmlentities"
require "readability"

def crawl(url_address)
self.errors = Array.new
begin
  begin
    url_address = URI.parse(url_address)
  rescue URI::InvalidURIError
    url_address = URI.decode(url_address)
    url_address = URI.encode(url_address)
    url_address = URI.parse(url_address)
  end
  url_address.normalize!
  stream = ""
  timeout(8) { stream = url_address.open(SHINSO_HEADERS) }
  if stream.size > 0
    url_crawled = URI.parse(stream.base_uri.to_s)
  else
    self.errors << "Server said status 200 OK but document file is zero bytes."
    return
  end
rescue Exception => exception
  self.errors << exception
  return
end
# extract information before html parsing
self.url_posted       = url_address.to_s
self.url_parsed       = url_crawled.to_s
self.url_host         = url_crawled.host
self.status           = stream.status
self.content_type     = stream.content_type
self.content_encoding = stream.content_encoding
self.charset          = stream.charset
if    stream.content_encoding.include?('gzip')
  document = Zlib::GzipReader.new(stream).read
elsif stream.content_encoding.include?('deflate')
  document = Zlib::Deflate.new().deflate(stream).read
#elsif stream.content_encoding.include?('x-gzip') or
#elsif stream.content_encoding.include?('compress')
else
  document = stream.read
end
self.charset_guess = CharGuess.guess(document)
if not self.charset_guess.blank? and (not self.charset_guess.downcase == 'utf-8' or not self.charset_guess.downcase == 'utf8')
  document = Iconv.iconv("UTF-8", self.charset_guess, document).to_s
end
document = Nokogiri::HTML.parse(document,nil,"utf8")
document.xpath('//script').remove
document.xpath('//SCRIPT').remove
for item in document.xpath('//*[translate(@src, "ABCDEFGHIJKLMNOPQRSTUVWXYZ", "abcdefghijklmnopqrstuvwxyz")]')
  item.set_attribute('src',make_absolute_address(item['src']))
end
document = document.to_s.gsub(/<!--(.|\s)*?-->/,'')
self.content = Nokogiri::HTML.parse(document,nil,"utf8")
end

Answer 3

The site seems to be doing some of the redirection logic with sessions. If you don't send back the session cookies they are sending on the first request you will end up in a redirect loop. IMHO it's a crappy implementation on their part.

However, I tried to pass the cookies back to them, but I didn't get it to work, so I can't be completely sure that that is all that's going on here.