Your best bet would be to set up redirect with your DNS provider, so it happens long before any request reaches your server. From the Heroku Dev Center:
Subdomain redirection results in a 301 permanent redirect to the specified subdomain for all requests to the naked domain so all current and future requests are properly routed and the full www hostname is displayed in the user’s location field.
DNSimple provides a convenient URL redirect seen here redirecting from
the heroku-sslendpoint.com
naked domain to the
www.heroku-sslendpoint.com
subdomain.
For proper configuration on Heroku the www subdomain should then be a
CNAME record reference to yourappname.herokuapp.com.
It's not just DNSimple that does this. My DNS provider is 123 Reg and they support it but call it web forwarding
.
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