Building a downloadable sitemap zip file in Heroku - ruby

Question

I'm building a web tool in Heroku / Ruby Sinatra that scrapes a web domain and downloads all specified filetypes (it should provide a zip file of the sitemap of the domain's filetypes to download).
I am trying to figure out how to build a ZipFile on Heroku. How do I set the home directory? Then once I have the ZipFile, how do I link to it so it's downloadable?
Here is some of the relavent code so far:
anemone.after_crawl do
puts "Crawl finished. Gathering files, preparing download..."
datasets.each do |url|
u = URI.parse(url.to_s)
Net::HTTP.start(u.host) { |http|
resp = http.get(u.path)
if u.path[0] == "/"
u.path[0] = ''
end
full_path = u.path.split("/")
i = 0
len = full_path.size
filename = full_path[-1]
Zip::ZipFile.open(u.host + ".zip", Zip::ZipFile::CREATE) {
|zipfile|
while i < (len-1) do
directory = full_path[i]
unless File.directory?(directory)
zipfile.mkdir(directory)
end
Dir.chdir directory
i+=1
end
zipfile.add(filename);
while (i > 0) do
Dir.chdir File.expand_path("..",Dir.pwd)
i-=1
end
}
}
end
end

Answer 1

The Heroku filesystem is mostly read-only, but you should be able to temporarily stash the zipfile on /tmp:
Zip::ZipFile.open("#{RAILS_ROOT}/tmp/" + u.host + ".zip", Zip::ZipFile::CREATE)
You'll probably want to use send_file in a "downloads" controller to allow users to download the file. You'll want to build in error handling in case the temporary file disappears before the user downloads it (e.g., if the dyno restarted between zipfile creation and download).
EDIT
The documentation I linked is apparently outdated. RAILS_ROOT is the Rails 2 way to refer to the directory root, but the Rails 3 way (Rails.root) doesn't work either--in Heroku it refers to the ./app folder.
However, you can use the Heroku base filesystem /tmp folder, like this:
Zip::ZipFile.open("/tmp/" + u.host + ".zip", Zip::ZipFile::CREATE)