How redirect_to works in Rails?

If you are a Rails developer, chances are you have already used redirect_to bunch of times. But have you ever wondered, how it works?

Suppose if you put this in your controller code and set the appropriate routing

def index
  redirect_to "https://www.google.com"
end

Your browser will redirect you to google.com, which is fine. But how does your browser know to redirect to google.com?

The magic lies here https://github.com/rails/rails/blob/b738f1930f3c82f51741ef7241c1fee691d7deb2/actionpack/lib/action_controller/metal/redirecting.rb#L58

The code is this

    def redirect_to(options = {}, response_options = {})
      raise ActionControllerError.new("Cannot redirect to nil!") unless options
      raise AbstractController::DoubleRenderError if response_body

      self.status        = _extract_redirect_to_status(options, response_options)
      self.location      = _compute_redirect_to_location(request, options)
      self.response_body = "<html><body>You are being <a href=\"#{ERB::Util.unwrapped_html_escape(response.location)}\">redirected</a>.</body></html>"
    end

Basically, the above code is setting the status as 302 by default. And location header to https://www.google.com. And the response body to

You are being <a href="https://www.google.com">redirected</a>.

So when the browser receives a status of 3xx with a location header, it redirects!

In the browser, if you see the network, it looks like this

As you can see it's setting the status to 302
and Location to https://www.google.com

I was unsuccessful in seeing the response body in the browser, maybe that's just the browser's behavior. Someone can confirm this?

But I could see response body in curl request

It looks like this

curl http://localhost:3000 -v
* Rebuilt URL to: http://localhost:3000/
*   Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 3000 (#0)
> GET / HTTP/1.1
> Host: localhost:3000
> User-Agent: curl/7.54.0
> Accept: */*
>
< HTTP/1.1 302 Found
< X-Frame-Options: SAMEORIGIN
< X-XSS-Protection: 1; mode=block
< X-Content-Type-Options: nosniff
< X-Download-Options: noopen
< X-Permitted-Cross-Domain-Policies: none
< Referrer-Policy: strict-origin-when-cross-origin
< Location: https://www.google.com
< Content-Type: text/html; charset=utf-8
< Cache-Control: no-cache
< X-Request-Id: 660668ae-1176-4770-8e82-a6bb303efbbc
< X-Runtime: 0.029982
< Transfer-Encoding: chunked
<
* Connection #0 to host localhost left intact
<html><body>You are being <a href="https://www.google.com">redirected</a>.</body></html>%

So with our new-found knowledge, how about making our own redirect_to behaviour in Rails? All we need to do is set a status and Location header

def index
  render plain: "You are being redirected to google.com", status: 302
  response.headers['Location'] = 'https://www.google.com'
end

The above method also works like redirect_to but looks a little ugly. But who cares :p

You can read more about how redirect works here https://developer.mozilla.org/en-US/docs/Web/HTTP/Redirections

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How redirect_to works in Rails?

vamsi pavan mahesh gunturu

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