blob: 0603e746a339805507e0cd9b07df7d92ded50766 [file] [log] [blame]
# Copyright 2018 The Chromium OS Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
import socket
import threading
import Queue
_BUF_SIZE = 4096
class FakePrinter():
A fake printer (server).
It starts a thread that listens on given localhost's port and saves
incoming documents in the internal queue. Documents can be fetched from
the queue by calling the fetch_document() method. At the end, the printer
must be stopped by calling the stop() method. The stop() method is called
automatically when the object is managed by "with" statement.
See for examples.
def __init__(self, port):
Initialize fake printer.
It configures the socket and starts the printer. If no exceptions
are thrown (the method succeeded), the printer must be stopped by
calling the stop() method.
@param port: port number on which the printer is supposed to listen
@raises socket or thread related exception in case of failure
# If set to True, the printer is stopped either by invoking stop()
# method or by an internal error
self._stopped = False
# It is set when printer is stopped because of some internal error
self._error_message = None
# An internal queue with printed documents
self._documents = Queue.Queue()
# Create a TCP/IP socket
self._socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
# Bind the socket to the port
self._socket.bind( ('localhost', port) )
# Start thread
self._thread = threading.Thread(target = self._thread_read_docs)
# failure - the socket must be closed before exit
# These methods allow to use the 'with' statement to automaticaly stop
# the printer
def __enter__(self):
return self
def __exit__(self, exc_type, exc_value, traceback):
def stop(self):
Stops the printer.
self._stopped = True
def fetch_document(self, timeout):
Fetches the next document from the internal queue.
This method returns the next document and removes it from the internal
queue. If there is no documents in the queue, it blocks until one
arrives. If waiting time exceeds a given timeout, an exception is
@param timeout: max waiting time in seconds
@returns next document from the internal queue
@raises Exception if the timeout was reached
return self._documents.get(block=True, timeout=timeout)
except Queue.Empty:
# Builds a message for the exception
message = 'Timeout occured when waiting for the document. '
if self._stopped:
message += 'The fake printer was stopped '
if self._error_message is None:
message += 'by the stop() method.'
message += 'because of the error: %s.' % self._error_message
message += 'The fake printer is in valid state.'
# Raises and exception
raise Exception(message)
def _read_whole_document(self):
Reads a document from the printer's socket.
It assumes that operation on sockets may timeout.
@returns whole document or None, if the printer was stopped
# Accepts incoming connection
while True:
(connection, client_address) = self._socket.accept()
# success - exit the loop
except socket.timeout:
# exit if the printer was stopped, else return to the loop
if self._stopped:
return None
# Reads document
document = ''
while True:
data = connection.recv(_BUF_SIZE)
# success - check data and continue
if not data:
# we got the whole document - exit the loop
# save chunk of the document and return to the loop
document += data
except socket.timeout:
# exit if the printer was stopped, else return to the loop
if self._stopped:
return None
# Closes connection & returns document
return document
def _thread_read_docs(self):
Reads documents from the printer's socket and adds them to the
internal queue.
It exits when the printer is stopped by the stop() method.
In case of any error (exception) it stops the printer and exits.
# Listen for incoming printer request.
# All following socket's methods throw socket.timeout after
# 500 miliseconds
while True:
# Reads document from the socket
document = self._read_whole_document()
# 'None' means that the printer was stopped -> exit
if document is None:
# Adds documents to the internal queue
except BaseException as e:
# Error occured, the printer must be stopped -> exit
self._error_message = str(e)
self._stopped = True
# Closes socket before the exit