How to make a HTTP request using Ruby on Rails?

You can use Ruby's Net::HTTP class:

require 'net/http'

url = URI.parse('http://www.example.com/index.html')
req = Net::HTTP::Get.new(url.to_s)
res = Net::HTTP.start(url.host, url.port) {|http|
  http.request(req)
}
puts res.body

Net::HTTP is built into Ruby, but let's face it, often it's easier not to use its cumbersome 1980s style and try a higher level alternative:

HTTP Gem

HTTParty

RestClient

Excon

Feedjira (RSS only)

OpenURI is the best; it's as simple as

require 'open-uri'
response = open('http://example.com').read

require 'net/http'
result = Net::HTTP.get(URI.parse('http://www.example.com/about.html'))
# or
result = Net::HTTP.get(URI.parse('http://www.example.com'), '/about.html')

I prefer httpclient over Net::HTTP.

client = HTTPClient.new
puts client.get_content('http://www.example.com/index.html')

HTTParty is a good choice if you're making a class that's a client for a service. It's a convenient mixin that gives you 90% of what you need. See how short the Google and Twitter clients are in the examples.

And to answer your second question: no, I wouldn't put this functionality in a controller--I'd use a model instead if possible to encapsulate the particulars (perhaps using HTTParty) and simply call it from the controller.

Here is the code that works if you are making a REST api call behind a proxy:

require "uri"
require 'net/http'

proxy_host = '<proxy addr>'
proxy_port = '<proxy_port>'
proxy_user = '<username>'
proxy_pass = '<password>'

uri = URI.parse("https://saucelabs.com:80/rest/v1/users/<username>")
proxy = Net::HTTP::Proxy(proxy_host, proxy_port, proxy_user, proxy_pass)

req = Net::HTTP::Get.new(uri.path)
req.basic_auth(<sauce_username>,<sauce_password>)

result = proxy.start(uri.host,uri.port) do |http|
http.request(req)
end

puts result.body

My favorite two ways to grab the contents of URLs are either OpenURI or Typhoeus.

OpenURI because it's everywhere, and Typhoeus because it's very flexible and powerful.