data/exec_standard_entrypoint.rb.erb

# Copyright 2019 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

require "webrick"
require "monitor"
require "json"

SECRET = <%= secret %>
COMMAND = Array(<%= command %>)

port = Integer ENV["PORT"]
server = ::WEBrick::HTTPServer.new Port: port

Status = ::Struct.new :out_lines, :err_lines, :exit_status, :pid, :start_time
$status = Status.new [], [], nil, nil, nil
$status.extend ::MonitorMixin

def do_start
  $status.synchronize do
    return unless $status.pid.nil?
  end
  $stdout.puts "Executing: #{COMMAND.inspect}"
  $stdout.flush
  rout, wout = ::IO.pipe
  rerr, werr = ::IO.pipe
  ::Thread.new do
    rout.each_line do |line|
      $status.synchronize { $status.out_lines << line }
      $stdout.puts line
      $stdout.flush
    end
  end
  ::Thread.new do
    rerr.each_line do |line|
      $status.synchronize { $status.err_lines << line }
      $stderr.puts line
      $stderr.flush
    end
  end
  start_time = Time.now.to_i
  pid = ::Process.spawn *COMMAND, err: werr, out: wout
  werr.close
  wout.close
  $status.synchronize do
    $status.pid = pid
    $status.start_time = start_time
  end
  ::Thread.new do
    _pid, status = ::Process.wait2 pid
    $status.synchronize do
      $status.exit_status = status.exitstatus
    end
  end
end

def get_status outpos: 0, errpos: 0
  outlines, errlines, status, start_time =
    $status.synchronize do
      [
        $status.out_lines[outpos..-1],
        $status.err_lines[errpos..-1],
        $status.exit_status,
        $status.start_time
      ]
    end
  {
    "outpos" => outpos + outlines.size,
    "errpos" => errpos + errlines.size,
    "outlines" => outlines,
    "errlines" => errlines,
    "status" => status,
    "time" => Time.now.to_i - start_time
  }
end

server.mount_proc "/_ah/start" do |req, res|
  do_start
end

server.mount_proc "/#{SECRET}" do |req, res|
  do_start
  status = get_status outpos: req.query["outpos"].to_i,
                      errpos: req.query["errpos"].to_i
  res.body = JSON.dump status
end

server.mount_proc "/#{SECRET}/kill" do |req, res|
  unless req.request_method == "POST"
    res.status = 404
    return
  end
  $status.synchronize do
    if $status.pid.nil?
      res.status = 404
      return
    end
    ::Process.kill "SIGTERM", $status.pid
  end
end

begin
  server.start
ensure
  server.shutdown
end