zc.monitor 0.4.0.post1

A network-accessible command-line monitoring interface.

Monitor Server

The monitor server is a server that provides a command-line interface to request various bits of information. The server is zc.ngi based, so we can use the zc.ngi testing infrastructure to demonstrate it.

>>> import zc.ngi.testing
>>> import zc.monitor

>>> connection = zc.ngi.testing.TextConnection()
>>> server = zc.monitor.Server(connection)

The server supports an extensible set of commands. It looks up commands as named zc.monitor.interfaces.IMonitorPlugin “utilities”, as defined by the zope.component package.

To see this, we’ll create a hello plugin:

>>> def hello(connection, name='world'):
...     """Say hello
...
...     Provide a name if you're not the world.
...     """
...     connection.write("Hi %s, nice to meet ya!\n" % name)

and register it:

>>> zc.monitor.register(hello)

When we register a command, we can provide a name. To see this, we’ll register hello again:

>>> zc.monitor.register(hello, 'hi')

Now we can give the hello command to the server:

>>> connection.test_input('hi\n')
Hi world, nice to meet ya!
-> CLOSE

We can pass a name:

>>> connection = zc.ngi.testing.TextConnection()
>>> server = zc.monitor.Server(connection)
>>> connection.test_input('hello Jim\n')
Hi Jim, nice to meet ya!
-> CLOSE

The server comes with a few basic commands. Let’s register them so we can see what they do. We’ll use the simplfied registration interface:

>>> zc.monitor.register_basics()

The first is the help command. Giving help without input, gives a list of available commands:

>>> connection = zc.ngi.testing.TextConnection()
>>> server = zc.monitor.Server(connection)
>>> connection.test_input('help\n')
Supported commands:
  hello -- Say hello
  help -- Get help about server commands
  hi -- Say hello
  interactive -- Turn on monitor's interactive mode
  quit -- Quit the monitor
-> CLOSE

We can get detailed help by specifying a command name:

>>> connection = zc.ngi.testing.TextConnection()
>>> server = zc.monitor.Server(connection)
>>> connection.test_input('help help\n')
Help for help:
<BLANKLINE>
Get help about server commands
<BLANKLINE>
    By default, a list of commands and summaries is printed.  Provide
    a command name to get detailed documentation for a command.
<BLANKLINE>
-> CLOSE

>>> connection = zc.ngi.testing.TextConnection()
>>> server = zc.monitor.Server(connection)
>>> connection.test_input('help hello\n')
Help for hello:
<BLANKLINE>
Say hello
<BLANKLINE>
    Provide a name if you're not the world.
<BLANKLINE>
-> CLOSE

The interactive command switches the monitor into interactive mode. As seen above, the monitor usually responds to a single command and then closes the connection. In “interactive mode”, the connection is not closed until the quit command is used. This can be useful when accessing the monitor via telnet for diagnostics.

>>> connection = zc.ngi.testing.TextConnection()
>>> server = zc.monitor.Server(connection)
>>> connection.test_input('interactive\n')
Interactive mode on.  Use "quit" To exit.
>>> connection.test_input('help interactive\n')
Help for interactive:
<BLANKLINE>
Turn on monitor's interactive mode
<BLANKLINE>
    Normally, the monitor releases the connection after a single command.
    By entering the interactive mode, the monitor will not end the connection
    until you enter the "quit" command.
<BLANKLINE>
    In interactive mode, an empty line repeats the last command.
<BLANKLINE>
>>> connection.test_input('help quit\n')
Help for quit:
<BLANKLINE>
Quit the monitor
<BLANKLINE>
    This is only really useful in interactive mode (see the "interactive"
    command).
<BLANKLINE>

Notice that the result of the commands did not end with “-> CLOSE”, which would have indicated a closed connection.

Also notice that the interactive mode allows you to repeat commands.

>>> connection.test_input('hello\n')
Hi world, nice to meet ya!
>>> connection.test_input('\n')
Hi world, nice to meet ya!
>>> connection.test_input('hello Jim\n')
Hi Jim, nice to meet ya!
>>> connection.test_input('\n')
Hi Jim, nice to meet ya!

Now we will use quit to close the connection.

>>> connection.test_input('quit\n')
Goodbye.
-> CLOSE

Finally, it’s worth noting that exceptions will generate a traceback on the connection.

>>> connection = zc.ngi.testing.TextConnection()
>>> server = zc.monitor.Server(connection)
>>> connection.test_input('hello Jim 42\n') # doctest: +ELLIPSIS
Traceback (most recent call last):
...
TypeError: hello() takes at most 2 arguments (3 given)
<BLANKLINE>
-> CLOSE

Command loops

Using the “MORE” mode, commands can signal that they want to claim all future user input. We’ll implement a silly example to demonstrate how it works.

Here’s a command that implements a calculator.

>>> PROMPT = '.'
>>> def calc(connection, *args):
...     if args and args[0] == 'quit':
...         return zc.monitor.QUIT_MARKER
...
...     if args:
...         connection.write(str(eval(''.join(args))))
...         connection.write('\n')
...
...     connection.write(PROMPT)
...     return zc.monitor.MORE_MARKER

If we register this command…

>>> zc.monitor.register(calc)

…we can invoke it and we get a prompt.

>>> connection = zc.ngi.testing.TextConnection()
>>> server = zc.monitor.Server(connection)
>>> connection.test_input('calc\n')
.

If we then give it more input we get the result plus another prompt.

>>> connection.test_input('2+2\n')
4
.

>>> connection.test_input('4*2\n')
8
.

Once we’re done we can tell the calculator to let us go.

>>> connection.test_input('quit\n')
-> CLOSE

Start server

>>> import time
>>> import zope.testing.loggingsupport, logging
>>> loghandler = zope.testing.loggingsupport.InstalledHandler(
...                  None, level=logging.INFO)

>>> zc.monitor.start(9644)
('', 9644)

>>> print loghandler
zc.ngi.async.server INFO
  listening on ('', 9644)

>>> zc.monitor.last_listener.close()
>>> zc.monitor.last_listener = None
>>> time.sleep(0.1)

>>> loghandler.clear()

>>> zc.monitor.start(('127.0.0.1', 9644))
('127.0.0.1', 9644)

>>> print loghandler
zc.ngi.async.server INFO
  listening on ('127.0.0.1', 9644)

>>> zc.monitor.last_listener.close()
>>> zc.monitor.last_listener = None
>>> time.sleep(0.1)

Bind to port 0:

>>> addr = zc.monitor.start(0)
>>> addr == zc.monitor.last_listener.address
True

>>> zc.monitor.last_listener.close()
>>> zc.monitor.last_listener = None
>>> time.sleep(0.1)

Trying to rebind to a port in use:

>>> loghandler.clear()

>>> zc.monitor.start(('127.0.0.1', 9644))
('127.0.0.1', 9644)

>>> zc.monitor.start(('127.0.0.1', 9644))
False

>>> print loghandler
zc.ngi.async.server INFO
  listening on ('127.0.0.1', 9644)
zc.ngi.async.server WARNING
  unable to listen on ('127.0.0.1', 9644)
root WARNING
  unable to start zc.monitor server because the address ('127.0.0.1', 9644) is in use.

>>> zc.monitor.last_listener.close()
>>> zc.monitor.last_listener = None
>>> time.sleep(0.1)

>>> loghandler.uninstall()

Change History

0.4.0.post1 (2019-12-06)

• Fix change log on PyPI.

0.4.0 (2019-12-06)

• Use new Python 2.6/3.x compatible exception syntax. (This does not mean that this package is already Python 3 compatible.)

0.3.1 (2012-04-27)

• When binding the monitor to a Unix-domain socket, remove an existing socket at the same path so the bind is successful. This may affect existing usage with respect to zopectl debug behavior, but will be more predictable.

0.3.0 (2011-12-12)

• Added a simplified registration interface.

0.2.1 (2011-12-10)

• Added an address option to start to be able to specify an adapter to bind to.

• start now returns the address being listened on, which is useful when binding to port 0.

• Using Python’s doctest module instead of depreacted zope.testing.doctest.

0.2.0 (2009-10-28)

• Add the “MORE” mode so commands can co-opt user interaction

0.1.2 (2008-09-15)

• Bugfix: The z3monitor server lacked a handle_close method, which caused errors to get logged when users closed connections before giving commands.

0.1.1 (2008-09-14)

• Bugfix: fixed and added test for regression in displaying tracebacks.

0.1.0 (2008-09-14)

Initial release