Native messaging host

test-native.pl

#!/usr/bin/env perl
# klg, Jun 2017
use strict;
use JSON;

my $j = JSON->new->utf8->allow_nonref;
my $c = 0;

local $| = 1;
while (1) {
  sysread \*STDIN, $_, 4 or last;
  sysread \*STDIN, $_, unpack 'L' or die $!;
  my $msg = $j->decode($_);
  print pack 'L/a', $j->encode({
      echo => $msg,
      count => ++$c,
      argv => \@ARGV,
      a => chr 261,
      v => "perl $^V",
      pid => $$
    });
}

test-native.py

#!/usr/bin/env python3
# klg, May 2018
import os
import sys
import struct
import json

stdin = os.fdopen(sys.stdin.fileno(), 'rb', 0)
stdout = os.fdopen(sys.stdout.fileno(), 'wb', 0)

try:
    chr = unichr
except:
    pass

cnt = 0

while True:
    tag = stdin.read(4)
    if not tag:
        sys.exit()
    length = struct.unpack('=L', tag)[0]
    msg = json.loads(stdin.read(length))
    cnt += 1
    res = json.dumps({
        'echo': msg,
        'count': cnt,
        'argv': sys.argv,
        'a': chr(261),
        'v': 'python '+sys.version,
        'pid': os.getpid(),
    })
    res = res.encode('UTF-8')
    stdout.write(struct.pack('=L', len(res)) + res)

test-native.rb

#!/usr/bin/env ruby
# klg, May 2018
require 'json'

cnt = 0

loop do
  len = $stdin.sysread(4).unpack('L')[0]
  msg = JSON.parse($stdin.sysread(len))
  res = JSON.generate({
    echo: msg,
    count: cnt += 1,
    argv: ARGV,
    a: [261].pack('U'),
    v: "ruby #{RUBY_VERSION}",
    pid: Process.pid
  })
  $stdout.syswrite([res.bytes.length, res].pack 'La*')
rescue EOFError
  exit
end

Note that Python version above works just fine with either Python 2 or 3; there's no need to make is as ridiculous as they did in example at MDN.