A little server example extracted from un.rb for barg

server.rb

# frozen_string_literal: false
#
# = un.rb
#
# Copyright (c) 2003 WATANABE Hirofumi <eban@ruby-lang.org>
#
# This program is free software.
# You can distribute/modify this program under the same terms of Ruby.
#
#   ruby -run -e httpd -- [OPTION] DocumentRoot

require 'fileutils'
require 'optparse'

def setup(options = "", *long_options)
  caller = caller_locations(1, 1)[0].label
  opt_hash = {}
  argv = []
  OptionParser.new do |o|
    options.scan(/.:?/) do |s|
      opt_name = s.delete(":").intern
      o.on("-" + s.tr(":", " ")) do |val|
        opt_hash[opt_name] = val
      end
    end
    long_options.each do |s|
      opt_name, arg_name = s.split(/(?=[\s=])/, 2)
      opt_name.delete_prefix!('--')
      s = "--#{opt_name.gsub(/([A-Z]+|[a-z])([A-Z])/, '\1-\2').downcase}#{arg_name}"
      puts "#{opt_name}=>#{s}" if $DEBUG
      opt_name = opt_name.intern
      o.on(s) do |val|
        opt_hash[opt_name] = val
      end
    end
    o.on("-v") do opt_hash[:verbose] = true end
    o.on("--help") do
      UN.help([caller])
      exit
    end
    o.order!(ARGV) do |x|
      if /[*?\[{]/ =~ x
        argv.concat(Dir[x])
      else
        argv << x
      end
    end
  end
  yield argv, opt_hash
end

setup("", "BindAddress=ADDR", "Port=PORT", "MaxClients=NUM", "TempDir=DIR",
      "DoNotReverseLookup", "RequestTimeout=SECOND", "HTTPVersion=VERSION",
      "ServerName=NAME", "ServerSoftware=NAME",
      "SSLCertificate=CERT", "SSLPrivateKey=KEY") do
  |argv, options|
  require 'webrick'
  opt = options[:RequestTimeout] and options[:RequestTimeout] = opt.to_i
  [:Port, :MaxClients].each do |name|
    opt = options[name] and (options[name] = Integer(opt)) rescue nil
  end
  if cert = options[:SSLCertificate]
    key = options[:SSLPrivateKey] or
      raise "--ssl-private-key option must also be given"
    require 'webrick/https'
    options[:SSLEnable] = true
    options[:SSLCertificate] = OpenSSL::X509::Certificate.new(File.read(cert))
    options[:SSLPrivateKey] = OpenSSL::PKey.read(File.read(key))
    options[:Port] ||= 8443   # HTTPS Alternate
  end
  options[:Port] ||= 8080     # HTTP Alternate
  options[:DocumentRoot] = argv.shift || '.'
  s = WEBrick::HTTPServer.new(options)
  shut = proc {s.shutdown}
  siglist = %w"TERM QUIT"
  siglist.concat(%w"HUP INT") if STDIN.tty?
  siglist &= Signal.list.keys
  siglist.each do |sig|
    Signal.trap(sig, shut)
  end
  s.start
end