An sample ICAP server written in Ruby

icapserver.rb

require 'socket'

class ICAPServer
  def initialize(port = 1344)
    @server = TCPServer.new(port)
    puts "ICAP server started on port #{port}"
  end

  def run
    loop do
      client = @server.accept
      handle_request(client)
      client.close
    end
  end

  private

  def handle_request(client)
    request = client.gets
    puts "Received request: #{request.strip}"

    if request.start_with?('OPTIONS')
      handle_options(client)
    elsif request.start_with?('REQMOD')
      handle_reqmod(client)
    else
      client.puts "ICAP/1.0 400 Bad Request\r\n\r\n"
    end
  end

  def handle_options(client)
    response = <<~OPTIONS
      ICAP/1.0 200 OK
      Methods: REQMOD RESPMOD
      Service: Ruby ICAP Server
      Preview: 0
      Transfer-Preview: *
      Allow: 204
      ISTag: "RubyICAPServer"
      
    OPTIONS
    client.puts response
    puts "Responded to OPTIONS request"
  end
  def handle_reqmod(client)
    headers = []
    while (line = client.gets.strip) != ""
      headers << line
    end

    # Log and modify the request (example header addition)
    puts "Original Headers:\n#{headers.join("\n")}"
    headers << "X-Modified-By: Ruby ICAP Server"

    # Send the modified response back
    response = <<~REQMOD
      ICAP/1.0 200 OK
      Encapsulated: req-hdr=0, null-body=#{headers.join.length}

      #{headers.join("\r\n")}\r\n
    REQMOD

    client.puts response
    puts "Modified request sent back"
  end
end

server = ICAPServer.new
server.run