Automatically Insert ETag (asset fingerprinting) as comment at top of the resource

Question

How to ask Play to automatically insert the file\'s ETag as a comment near the top of the file without using third party plugins?

E.g., for a HTML resource, insert

Answer 1

In conf/routes add the following:

GET  /resources/*file  controllers.Resources.at(file)

In app/controllers/Resources controller:

package controllers

import play.api.mvc._

object Resources extends Controller {
  def at(path: String): Action = {
    // calculate ETag
    val etag = ETag(path)
    // stream file with ETag inserted
    Ok(... <!-- ETag: etag --> ...)
  }
}