Source code for plainbox.impl.commands

# This file is part of Checkbox.
#
# Copyright 2012 Canonical Ltd.
# Written by:
#   Zygmunt Krynicki <zygmunt.krynicki@canonical.com>
#
# Checkbox is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License version 3,
# as published by the Free Software Foundation.

#
# Checkbox is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with Checkbox.  If not, see <http://www.gnu.org/licenses/>.

"""
:mod:`plainbox.impl.commands` -- shared code for plainbox sub-commands
======================================================================

.. warning::

    THIS MODULE DOES NOT HAVE STABLE PUBLIC API
"""

from abc import abstractmethod, ABCMeta
import argparse
import errno
import logging
import os
import pdb
import sys

from plainbox.impl.logging import adjust_logging
from plainbox.impl.providers.v1 import all_providers
from plainbox.impl.providers.special import CheckBoxSrcProvider
from plainbox.impl.providers.special import StubBoxProvider


logger = logging.getLogger("plainbox.commands")


[docs]class PlainBoxCommand(metaclass=ABCMeta): """ Simple interface class for plainbox commands. Command objects like this are consumed by PlainBoxTool subclasses to implement hierarchical command system. The API supports arbitrary many sub commands in arbitrary nesting arrangement. """ @abstractmethod
[docs] def invoked(self, ns): """ Implement what should happen when the command gets invoked The ns is the namespace produced by argument parser """
@abstractmethod
[docs] def register_parser(self, subparsers): """ Implement what should happen to register the additional parser for this command. The subparsers argument is the return value of ArgumentParser.add_subparsers() """
[docs] def autopager(self): """ Enable automatic pager. This invokes :func:`autopager()` which wraps execution in a pager program so that long output is not a problem to read. Do not call this in interactive commands. """ autopager()
[docs]class PlainBoxToolBase(metaclass=ABCMeta): """ Base class for implementing commands like 'plainbox'. The tools support a variety of sub-commands, logging and debugging support. If argcomplete module is available and used properly in the shell then advanced tab-completion is also available. There are three methods to implement for a basic tool. Those are: 1. :meth:`get_config_cls()` -- to know which config to use 2. :meth:`get_exec_name()` -- to know how the command will be called 3. :meth:`add_subcommands()` -- to add some actual commands to execute This class has some complex control flow to support important and interesting use cases. There are some concerns to people that subclass this in order to implement their own command line tools. The first concern is that input is parsed with two parsers, the early parser and the full parser. The early parser quickly checks for a fraction of supported arguments and uses that data to initialize environment before construction of a full parser is possible. The full parser sees the reminder of the input and does not re-parse things that where already handled. The second concern is that this command natively supports the concept of a config object and a provider object. This may not be desired by all users but it is the current state as of this writing. This means that by the time eary init is done we have a known provider and config objects that can be used to instantiate command objects in :meth:`add_subcommands()`. This API might change when full multi-provider is available but details are not known yet. """ def __init__(self): """ Initialize all the variables, real stuff happens in main() """ self._early_parser = None # set in _early_init() self._config = None # set in _late_init() self._provider_list = [] # reset in _late_init() self._parser = None # set in _late_init()
[docs] def main(self, argv=None): """ Run as if invoked from command line directly """ # Another try/catch block for catching KeyboardInterrupt # This one is really only meant for the early init abort # (when someone runs main but bails out before we really # get to the point when we do something useful and setup # all the exception handlers). try: self.early_init() early_ns = self._early_parser.parse_args(argv) self.late_init(early_ns) logger.debug("parsed early namespace: %s", early_ns) # parse the full command line arguments, this is also where we # do argcomplete-dictated exit if bash shell completion # is requested ns = self._parser.parse_args(argv) logger.debug("parsed full namespace: %s", ns) self.final_init(ns) except KeyboardInterrupt: pass else: return self.dispatch_and_catch_exceptions(ns)
@classmethod @abstractmethod
[docs] def get_config_cls(cls): """ Get the Config class that is used by this implementation. This can be overriden by subclasses to use a different config class that is suitable for the particular application. """
@classmethod @abstractmethod
[docs] def get_exec_name(cls): """ Get the name of this executable """
@classmethod @abstractmethod
[docs] def get_exec_version(cls): """ Get the version reported by this executable """
@abstractmethod
[docs] def add_subcommands(self, subparsers): """ Add top-level subcommands to the argument parser. This can be overriden by subclasses to use a different set of top-level subcommands. """
[docs] def early_init(self): """ Do very early initialization. This is where we initalize stuff even without seeing a shred of command line data or anything else. """ self._early_parser = self.construct_early_parser()
[docs] def late_init(self, early_ns): """ Initialize with early command line arguments being already parsed """ adjust_logging( level=early_ns.log_level, trace_list=early_ns.trace, debug_console=early_ns.debug_console) # Load plainbox configuration self._config = self.get_config_cls().get() # If the default value of 'None' was set for the checkbox (provider) # argument then load the actual provider name from the configuration # object (default for that is 'auto'). if early_ns.checkbox is None: early_ns.checkbox = self._config.default_provider assert early_ns.checkbox in ('auto', 'src', 'deb', 'stub', 'ihv') # Decide where to load all of the providers from if early_ns.checkbox == 'auto': if CheckBoxSrcProvider.exists(): self._provider_list = [CheckBoxSrcProvider()] else: all_providers.load() self._provider_list = [ plugin.plugin_object for plugin in all_providers.get_all_plugins()] elif early_ns.checkbox == 'src': self._provider_list = [CheckBoxSrcProvider()] elif early_ns.checkbox == 'deb': all_providers.load() self._provider_list = [ plugin.plugin_object for plugin in all_providers.get_all_plugins()] elif early_ns.checkbox == 'stub': self._provider_list = [StubBoxProvider()] elif early_ns.checkbox == 'ihv': logger.warning( "The -c ihv option is deprecated and doesn't work anymore") if CheckBoxSrcProvider.exists(): self._provider_list = [CheckBoxSrcProvider()] else: all_providers.load() self._provider_list = [ plugin.plugin_object for plugin in all_providers.get_all_plugins()] # Construct the full command line argument parser self._parser = self.construct_parser()
[docs] def final_init(self, ns): """ Do some final initialization just before the command gets dispatched. This is empty here but maybe useful for subclasses. """
[docs] def construct_early_parser(self): """ Create a parser that captures some of the early data we need to be able to have a real parser and initialize the rest. """ parser = argparse.ArgumentParser(add_help=False) # Fake --help and --version parser.add_argument("-h", "--help", action="store_const", const=None) parser.add_argument("--version", action="store_const", const=None) self.add_early_parser_arguments(parser) # A catch-all net for everything else parser.add_argument("rest", nargs="...") return parser
[docs] def construct_parser(self): parser = argparse.ArgumentParser(prog=self.get_exec_name()) parser.add_argument( "--version", action="version", version=self.get_exec_version()) # Add all the things really parsed by the early parser so that it # shows up in --help and bash tab completion. self.add_early_parser_arguments(parser) subparsers = parser.add_subparsers() self.add_subcommands(subparsers) # Enable argcomplete if it is available. try: import argcomplete except ImportError: pass else: argcomplete.autocomplete(parser) return parser
[docs] def add_early_parser_arguments(self, parser): # Since we need a CheckBox instance to create the main argument parser # and we need to be able to specify where Checkbox is, we parse that # option alone before parsing everything else # TODO: rename this to -p | --provider parser.add_argument( '-c', '--checkbox', action='store', # TODO: have some public API for this, pretty please choices=['src', 'deb', 'auto', 'stub', 'ihv'], # None is a special value that means 'use whatever configured' default=None, help="where to find the installation of CheckBox.") group = parser.add_argument_group( title="logging and debugging") # Add the --log-level argument group.add_argument( "-l", "--log-level", action="store", choices=('DEBUG', 'INFO', 'WARNING', 'ERROR', 'CRITICAL'), default=None, help=argparse.SUPPRESS) # Add the --verbose argument group.add_argument( "-v", "--verbose", dest="log_level", action="store_const", const="INFO", help="be more verbose (same as --log-level=INFO)") # Add the --debug flag group.add_argument( "-D", "--debug", dest="log_level", action="store_const", const="DEBUG", help="enable DEBUG messages on the root logger") # Add the --debug flag group.add_argument( "-C", "--debug-console", action="store_true", help="display DEBUG messages in the console") # Add the --trace flag group.add_argument( "-T", "--trace", metavar="LOGGER", action="append", default=[], help=("enable DEBUG messages on the specified logger " "(can be used multiple times)")) # Add the --pdb flag group.add_argument( "-P", "--pdb", action="store_true", default=False, help="jump into pdb (python debugger) when a command crashes") # Add the --debug-interrupt flag group.add_argument( "-I", "--debug-interrupt", action="store_true", default=False, help="crash on SIGINT/KeyboardInterrupt, useful with --pdb")
[docs] def dispatch_command(self, ns): # Argh the horrror! # # Since CPython revision cab204a79e09 (landed for python3.3) # http://hg.python.org/cpython/diff/cab204a79e09/Lib/argparse.py # the argparse module behaves differently than it did in python3.2 # # In practical terms subparsers are now optional in 3.3 so all of the # commands are no longer required parameters. # # To compensate, on python3.3 and beyond, when the user just runs # plainbox without specifying the command, we manually, explicitly do # what python3.2 did: call parser.error(_('too few arguments')) if (sys.version_info[:2] >= (3, 3) and getattr(ns, "command", None) is None): self._parser.error(argparse._("too few arguments")) else: return ns.command.invoked(ns)
[docs] def dispatch_and_catch_exceptions(self, ns): try: return self.dispatch_command(ns) except SystemExit: # Don't let SystemExit be caught in the logic below, we really # just want to exit when that gets thrown. logger.debug("caught SystemExit, exiting") # We may want to raise SystemExit as it can carry a status code # along and we cannot just consume that. raise except BaseException as exc: logger.debug("caught %r, deciding on what to do next", exc) # For all other exceptions (and I mean all), do a few checks # and perform actions depending on the command line arguments # By default we want to re-raise the exception action = 'raise' # We want to ignore IOErrors that are really EPIPE if isinstance(exc, IOError): if exc.errno == errno.EPIPE: action = 'ignore' # We want to ignore KeyboardInterrupt unless --debug-interrupt # was passed on command line elif isinstance(exc, KeyboardInterrupt): if ns.debug_interrupt: action = 'debug' else: action = 'ignore' else: # For all other execptions, debug if requested if ns.pdb: action = 'debug' logger.debug("action for exception %r is %s", exc, action) if action == 'ignore': return 0 elif action == 'raise': logging.getLogger("plainbox.crashes").fatal( "Executable %r invoked with %r has crashed", self.get_exec_name(), ns, exc_info=1) raise elif action == 'debug': logger.error("caught runaway exception: %r", exc) logger.error("starting debugger...") pdb.post_mortem() return 1
[docs]def autopager(pager_list=['sensible-pager', 'less', 'more']): """ Enable automatic pager :param pager_list: List of pager programs to try. :returns: Nothing immedaitely if auto-pagerification cannot be turned on. This is true when running on windows or when sys.stdout is not a tty. This function executes the following steps: * A pager is selected * A pipe is created * The current process forks * The parent uses execlp() and becomes the pager * The child/python carries on the execution of python code. * The parent/pager stdin is connected to the childs stdout. * The child/python stderr is connected to parent/pager stdin only when sys.stderr is connected to a tty .. note:: Pager selection is influenced by the pager environment variabe. if set it will be prepended to the pager_list. This makes the expected behavior of allowing users to customize their environment work okay. .. warning:: This function must not be used for interactive commands. Doing so will prevent users from feeding any input to plainbox as all input will be "stolen" by the pager process. """ # If stdout is not connected to a tty or when running on win32, just return if not sys.stdout.isatty() or sys.platform == "win32": return # Check if the user has a PAGER set, if so, consider that the prime # candidate for the effective pager. pager = os.getenv('PAGER') if pager is not None: pager_list = [pager] + pager_list # Find the best pager based on user perferences and built-in knowledge try: pager_name, pager_pathname = find_exec(pager_list) except LookupError: # If none of the pagers are installed, just return return # Flush any pending output sys.stdout.flush() sys.stderr.flush() # Create a pipe that we'll use to glue ourselves to the pager read_end, write_end = os.pipe() # Fork so that we can have a pager process if os.fork() == 0: # NOTE: this is where plainbox will run # Rewire stdout and stderr (if a tty) to the pipe os.dup2(write_end, sys.stdout.fileno()) if sys.stderr.isatty(): os.dup2(write_end, sys.stderr.fileno()) # Close the unused end of the pipe os.close(read_end) else: # NOTE: this is where the pager will run # Rewire stdin to the pipe os.dup2(read_end, sys.stdin.fileno()) # Close the unused end of the pipe os.close(write_end) # Execute the pager os.execl(pager_pathname, pager_name)
[docs]def find_exec(name_list): """ Find the first executable from name_list in PATH :param name_list: List of names of executable programs to look for, in the order of preference. Only basenames should be passed here (not absolute pathnames) :returns: Tuple (name, pathname), if the executable can be found :raises: LookupError if none of the names in name_list are executable programs in PATH """ path_list = os.getenv('PATH', '').split(os.path.pathsep) for name in name_list: for path in path_list: pathname = os.path.join(path, name) if os.access(pathname, os.X_OK): return (name, pathname) raise LookupError( "Unable to find any of the executables {}".format( ", ".join(name_list)))