chrome/test/data/native_messaging/native_hosts/echo.py

#!/usr/bin/env python
# Copyright (c) 2012 The Chromium Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

# A simple native client in python.
# All this client does is echo the text it receives back at the extension.

import argparse
import base64
import json
import os
import platform
import sys
import struct

def WriteMessage(message):
  try:
    sys.stdout.write(struct.pack("I", len(message)))
    sys.stdout.write(message)
    sys.stdout.flush()
    return True
  except IOError:
    return False


def ParseArgs():
  parser = argparse.ArgumentParser()
  parser.add_argument('--parent-window', type=int)
  parser.add_argument('--reconnect-command')
  parser.add_argument('--native-messaging-connect-id')
  parser.add_argument('origin')
  return parser.parse_args()

def Main():
  message_number = 0

  args = ParseArgs()
  caller_url = args.origin

  if sys.argv[1] != args.origin:
    sys.stderr.write(
        "URL of the calling application is not specified as the first arg.\n")
    return 1

  # Verify that the process was started in the correct directory.
  cwd = os.getcwd()
  script_path = os.path.dirname(os.path.abspath(sys.argv[0]))
  if cwd.lower() != script_path.lower():
    sys.stderr.write('Native messaging host started in a wrong directory.')
    return 1

  # Verify that --parent-window parameter is correct.
  if platform.system() == 'Windows' and args.parent_window:
    import win32gui
    if not win32gui.IsWindow(args.parent_window):
      sys.stderr.write('Invalid --parent-window.\n')
      return 1

  reconnect_args = json.loads(base64.b64decode(
      args.reconnect_command)) if args.reconnect_command else None

  while 1:
    # Read the message type (first 4 bytes).
    text_length_bytes = sys.stdin.read(4)

    if len(text_length_bytes) == 0:
      break

    # Read the message length (4 bytes).
    text_length = struct.unpack('i', text_length_bytes)[0]

    # Read the text (JSON object) of the message.
    text = json.loads(sys.stdin.read(text_length).decode('utf-8'))

    # bigMessage() test sends a special message that is sent to verify that
    # chrome rejects messages that are too big. Try sending a message bigger
    # than 1MB after receiving a message that contains 'bigMessageTest'.
    if 'bigMessageTest' in text:
      text = {"key": "x" * 1024 * 1024}

    # "stopHostTest" verifies that Chrome properly handles the case when the
    # host quits before port is closed. When the test receives response it
    # will try sending second message and it should fail becasue the stdin
    # pipe will be closed at that point.
    if 'stopHostTest' in text:
      # Using os.close() here because sys.stdin.close() doesn't really close
      # the pipe (it just marks it as closed, but doesn't close the file
      # descriptor).
      os.close(sys.stdin.fileno())
      WriteMessage('{"stopped": true }')
      sys.exit(0)

    message_number += 1

    message = json.dumps({
        'id': message_number, 'echo': text, 'caller_url': caller_url,
        'args': reconnect_args, 'connect_id': args.native_messaging_connect_id,
    }).encode('utf-8')
    if not WriteMessage(message):
      break

if __name__ == '__main__':
  sys.exit(Main())