http_proxy.rb

require 'webrick'
require 'webrick/httpproxy'
require 'optparse'
require 'fileutils'

opts = {
  port: 8080,
  outdir: '.',
}
optparse = OptionParser.new("USAGE: #{$0} [OPTIONS]", 20)
optparse.on('-p PORT', Integer) {|x| opts[:port] = x }
optparse.on('-o DIR') {|x| opts[:outdir] = x }
begin
  optparse.parse!
rescue OptionParser::ParseError => e
  $stderr.puts e.to_s
  exit 1
end

auth_handler = proc do |req, res|
  req.header.delete('if-modified-since')
end

content_handler = proc do |req, res|
  next if req.request_method != 'GET'
  next if res.status != 200

  uri = req.request_uri
  path = File.join(opts[:outdir], uri.host)  # FIXME: Add port number
  path << uri.request_uri
  path << 'index.html' if path.end_with?('/')
  path.gsub!(/\?/, '__')

  dir = File.dirname(path)
  FileUtils.mkdir_p(dir) unless File.exists?(dir)
  IO.binwrite(path, res.body)

  if last_modified = res['last-modified']
    last_modified = Time.httpdate(last_modified)
    File.utime(Time.now, last_modified, path)
  end
end

server = WEBrick::HTTPProxyServer.new(
  Port: opts[:port],
  ProxyAuthProc: auth_handler,
  ProxyContentHandler: content_handler
)
trap(:INT) { server.shutdown }
server.start