Attach a pdf in asset pipeline using ActionMailer Rails 4 - ruby-on-rails

Question

I'm trying to attach a file to an email. The file is in assets/downloads/product.pdf
In the mailer, I have:
attachments["product.pdf"] = File.read(ActionController::Base.helpers.asset_path("product.pdf"))
I've tried:
attachments["product.pdf"] = File.read(ActionController::Base.helpers.asset_url("product.pdf"))
...and even:
attachments["product.pdf"] = File.read(ActionController::Base.helpers.compute_asset_host("product.pdf") + ActionController::Base.helpers.compute_asset_path("product.pdf"))
I always get the same error:
EmailJob crashed!
Errno::ENOENT: No such file or directory - //localhost:3000/assets/product.pdf
...or a variation on the theme. But even when I try using asset_url in the view or just put the url in the browser it works:
http://localhost:3000/assets/product.pdf
I've also tried using straight up:
File.read("app/assets/downloads/product.pdf")
File.read("downloads/product.pdf")
...which works in dev environment but not on staging server (heroku). Error is still:
Errno::ENOENT: No such file or directory - downloads/product-market-fit-storyboard.pdf
Also tried:
File.read("/downloads/product.pdf")
File.read("http://lvh.me:3000/assets/product.pdf")
...don't work at all.
Ideas?

Answer 1

you should use syntex like this.it is work for me may be will work for you also.
File.open(Dir.glob("#{Rails.root}/app/assets/downloads/product.pdf"), "r")

Answer 2

When using mailer, you shouldn't use assets pipline. Asset pipeline would be useful if you wanted to have link to a file inside your email. When rendering an email, action mailer has access to files in app directory.
Please read about attachments in action mailer guide. As you can see, you just need to pass path to a file, not url:
attachments['filename.jpg'] = File.read('/path/to/filename.jpg')