Ideally, you would set up rules like that in your web server configuration. Requests would become faster, because they would not even reach the rails stack. There would be no need to add any code to your app either.
However, if you are running in some restricted environment, like heroku, I'd advise adding a rack middleware. (Just for guidelines, can't guarantee if this particular code is bug free)
class Redirector
SUBDOMAIN = 'www'
def initialize(app)
@app = app
end
def call(env)
@env = env
if redirect?
redirect
else
@app.call(env)
end
end
private
def redirect?
# do some regex to figure out if you want to redirect
end
def redirect
headers = {
"location" => redirect_url
}
[302, headers, ["You are being redirected..."]] # 302 for temp, 301 for permanent
end
def redirect_url
scheme = @env["rack.url_scheme"]
if @env['SERVER_PORT'] == '80'
port = ''
else
port = ":#{@env['SERVER_PORT']}"
end
path = @env["PATH_INFO"]
query_string = ""
if !@env["QUERY_STRING"].empty?
query_string = "?" + @env["QUERY_STRING"]
end
host = "://#{SUBDOMAIN}." + domain # this is where we add the subdomain
"#{scheme}#{host}#{path}#{query_string}"
end
def domain
# extract domain from request or get it from an environment variable etc.
end
end
You can also test the whole thing in isolation
describe Redirector do
include Rack::Test::Methods
def default_app
lambda { |env|
headers = {'Content-Type' => "text/html"}
headers['Set-Cookie'] = "id=1; path=/\ntoken=abc; path=/; secure; HttpOnly"
[200, headers, ["default body"]]
}
end
def app()
@app ||= Rack::Lint.new(Redirector.new(default_app))
end
it "redirects unsupported subdomains" do
get "http://example.com/zomg?a=1"
last_response.status.should eq 301
last_response.header['location'].should eq "http://www.example.com/zomg?a=1"
end
# and so on
end
Then you can add it to production (or any preferred environments) only
# production.rb
# ...
config.middleware.insert_after 'ActionDispatch::Static', 'Redirector'
If you want to test it in development, add the same line to development.rb and add a record to your hosts file (usually /etc/hosts) to treat yoursubdomain.localhost as 127.0.0.1