Dead simple static file server using Ruby Rack, implementing Apaches RewriteMap feature using a plain-text mapping file.

config.ru

# frozen_string_literal: true

# Dead simple static file server using Ruby Rack implementing
# Apaches RewriteMap feature using a plain-text mapping file.
# See: https://httpd.apache.org/docs/current/rewrite/rewritemap.html#txt
#
# Deliberately does not use any caching, so keep the size of your redirects.txt
# in mind.
#
# Usage:
#   $ cat /var/www/redirects.txt
#   /foo/old%20path /foo/new-path/
#
#   $ RACK_ROOT=/var/www rackup config.ru

# $stdout.sync = true

PUBLIC_ROOT = ENV["RACK_ROOT"]
REDIRECTS_FILE = File.join(PUBLIC_ROOT, "redirects.txt")

INDEX = "index.html"
INDEX_PATH_SUFFIX = "/#{INDEX}".freeze

use Rack::CommonLogger
use Rack::Static, urls: [""], root: PUBLIC_ROOT, index: INDEX, cascade: true
run ->(env) do
  path_info = env["PATH_INFO"].delete_suffix(INDEX_PATH_SUFFIX)
  query_string = env["QUERY_STRING"]

  requested_url = "#{path_info}#{"?#{query_string}" unless query_string.empty?}"
  requested_slash_url = "#{File.join(path_info, '/')}#{"?#{query_string}" unless query_string.empty?}"

  redirect = nil
  File.open(REDIRECTS_FILE).each_line(chomp: true) { |line|
    orig, mapped = line.split(" ", 2)
    next unless [requested_url, requested_slash_url, path_info].include?(orig)

    redirect = mapped
    redirect << "?#{query_string}" if !query_string.empty? && !orig.include?("?")
    break
  }

  if redirect
    [301, { "Location" => redirect }, [""]]
  elsif File.directory?(File.join(PUBLIC_ROOT, path_info))
    [301, { "Location" => requested_slash_url }, [""]]
  else
    [404, {}, ["Not Found"]]
  end
end