Setup a mirror to use with $HOMEBREW_ARTIFACT_DOMAIN

brew-mirror-artifacts.rb

# Homebrew has $HOMEBREW_ARTIFACT_DOMAIN which allows using a mirror for downloads:
# 
# https://docs.brew.sh/Manpage#environment
#
# But no easy way to create such a mirror. This command which creates a mirror from
# all core formulae downloads. Pop it in /usr/local/Homebrew/Library/Homebrew/cmd/
# with a `chmod +x` and run `brew mirror-artifacts`.

require "formula"

base_path = Pathname.new(ENV.fetch("HOMEBREW_ARTIFACT_PATH") { Dir.pwd })

ohai "Mirroring all formula downloads to: #{path}"
Formula.core_files.each do |fi|
  begin
    f = Formula[fi]
  rescue Exception => e
    opoo "#{fi}: something goes wrong."
    puts e.message
    puts e.backtrace.inspect
    next
  end

  if f.downloader.is_a? CurlDownloadStrategy
    ohai "Mirroring #{f}"
    url = f.downloader.url
    uri = URI.parse(url)
    path = base_path.join(uri.host, uri.path.delete_prefix("/"))
    path.parent.mkpath
    curl_download url, to: path
  end
end