compute_asset_host

# File actionpack/lib/action_view/asset_paths.rb, line 107
    def compute_asset_host(source)
      if host = asset_host_config
        if host.respond_to?(:call)
          args = [source]
          arity = arity_of(host)
          if (arity > 1 || arity < -2) && !has_request?
            invalid_asset_host!("Remove the second argument to your asset_host Proc if you do not need the request, or make it optional.")
          end
          args << current_request if (arity > 1 || arity < 0) && has_request?
          host.call(*args)
        else
          (host =~ /%d/) ? host % (Zlib.crc32(source) % 4) : host
        end
      end
    end