A listen-only TCP server with configurable read options for testing

mock-tcpserver.rb

#!/usr/bin/env ruby

require 'socket'
require 'optparse'
require 'thread'

config = {
	port: 0,
	lag_ms: 0,
  jitter_ms: 0,
	buffer_bytes: 1024
}

OptionParser.new do |opts|
  opts.banner = "Usage: mock-tcpserver [options]"

  opts.on("-pPORT", '--port=PORT', 'specify port') do |port|
  	config[:port] = Integer(port)
  end

  opts.on("-lLAGMS", "--lag=LAGMS", 'specify lag in millis') do |lag_ms|
  	config[:lag_ms] = Integer(lag_ms)
  end

  opts.on("-jJITTERMS", "--jitter", 'specify max jitter in millis') do |jitter_ms|
    config[:jitter_ms] = Integer(jitter_ms)
  end

  opts.on("-bBUFFSIZE", '--buffer-size=BUFFERSIZE', 'specify buffer size in bytes') do |buffer_bytes|
  	config[:buffer_bytes] = Integer(buffer_bytes)
  end
end.parse!

global_mutex = Mutex.new
fmt_addr = -> (addr) { addr.include?(?:) ? "[#{addr}]" : addr }
sync_puts = -> (io, message) { global_mutex.synchronize { io.puts(message) } }

buffer_bytes = config[:buffer_bytes]

effective_lag_ms = case
when config[:lag_ms] <= 0    then ->() { 0 }
when config[:jitter_ms] <= 0 then ->() { config[:lag_ms] }
                             else ->() { config[:lag_ms] + Random.rand(config[:jitter_ms])}
end

server = TCPServer.new(config.fetch(:port, 0))
self_afam, self_port, self_hostname, self_addr = server.addr

sync_puts[$stderr, "LISTEN[#{self_afam}->#{fmt_addr[self_hostname]}:#{self_port}]"]

loop do
  Thread.start(server.accept) do |client|
  	peer_afam, peer_port, peer_hostname, peer_addr = client.peeraddr
  	client_desc = "#{peer_afam}<-#{fmt_addr[peer_hostname]}:#{peer_port}"
  	sync_puts[$stderr, "OPEN[#{client_desc}]"]

  	begin
  		loop do
  			buf = client.readpartial(buffer_bytes)
	  		sync_puts[$stderr, "BUFF[#{client_desc}]<-(#{buf.length})"]
        lag_ms = effective_lag_ms[]
  			sleep(Rational(lag_ms, 1000)) if (lag_ms > 0)
  		end
  	rescue EOFError
	  	sync_puts[$stderr, "EOF[#{client_desc}]"]
	  	client.close
  	end
  end
end