In Rails, I needed to take the request url and redirect the user to a new host with additional query parameters while passing the original path and query parameters.
For example, if the original request looked like:
I needed to redirect them to:
While this could be done with fancy string manipulation, I figured there had to be a cleaner and less error prone way.
There is a great utility in Ruby Core to handle URL manipulation. Unfortunately, it isn’t well documented.
There is a kernal level method named URI which parses the full url and breaks it down into parts
# request.url = http://www.mystore.com/cart?sort=desc uri = URI(request.url) puts uri.host # www.mystore.com puts uri.scheme # http puts uri.query # sort=desc
To swap the host and scheme was easy enough
uri.host = "mobile.mystore.com" uri.scheme = "https"
To modify the query parameters, we had to consider the possiblity of no parameters. In that case, the uri.query would be nil. The query parameters are only broken down into a string, so we have to split, add and join them back together.
query = uri.query ? uri.query.split('&') :  query << "view=ipad" uri.query = query.join('&')
Then we just have to reconstruct the url and redirect the user
redirect_to uri.to_s # https://mobile.mystore.com/cart?sort=desc&view=ipad
There is always a cleaner way.