buildstream/plugin.py

#!/usr/bin/env python3
#
#  Copyright (C) 2017 Codethink Limited
#
#  This program is free software; you can redistribute it and/or
#  modify it under the terms of the GNU Lesser General Public
#  License as published by the Free Software Foundation; either
#  version 2 of the License, or (at your option) any later version.
#
#  This library 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
#  Lesser General Public License for more details.
#
#  You should have received a copy of the GNU Lesser General Public
#  License along with this library. If not, see <http://www.gnu.org/licenses/>.
#
#  Authors:
#        Tristan Van Berkom <tristan.vanberkom@codethink.co.uk>
"""
Plugin
=======
BuildStream supports third party plugins to define additional kinds of
elements and sources.

Plugin Structure
----------------
A plugin should consist of a `setuptools package
<http://setuptools.readthedocs.io/en/latest/setuptools.html>`_ that
advertises contained plugins using `entry points
<http://setuptools.readthedocs.io/en/latest/setuptools.html#dynamic-discovery-of-services-and-plugins>`_.

A plugin entry point must be a module that extends a class in the
:ref:`core_framework` to be discovered by BuildStream. A YAML file
defining plugin default settings with the same name as the module can
also be defined in the same directory as the plugin module.

.. note::

    BuildStream does not support function/class entry points.

A sample plugin could be structured as such:

.. code-block:: text

    .
    ├── elements
    │   ├── autotools.py
    │   ├── autotools.yaml
    │   └── __init__.py
    ├── MANIFEST.in
    └── setup.py

The setuptools configuration should then contain at least:

setup.py:

.. literalinclude:: ../source/sample_plugin/setup.py
   :language: python

MANIFEST.in:

.. literalinclude:: ../source/sample_plugin/MANIFEST.in
   :language: text

Class Reference
---------------
"""

import os
import subprocess
from contextlib import contextmanager
from weakref import WeakValueDictionary

from . import _yaml, _signals
from . import utils
from ._exceptions import PluginError, ImplError
from ._message import Message, MessageType


class Plugin():
    """Plugin()

    Base Plugin class.

    Some common features to both Sources and Elements are found
    in this class.

    .. note::

        Derivation of plugins is not supported. Plugins may only
        derive from the base :mod:`Source <buildstream.source>` and
        :mod:`Element <buildstream.element>` types, and any convenience
        subclasses (like :mod:`BuildElement <buildstream.buildelement>`)
        which are included in the buildstream namespace.
    """

    BST_REQUIRED_VERSION_MAJOR = 0
    """Minimum required major version"""

    BST_REQUIRED_VERSION_MINOR = 0
    """Minimum required minor version"""

    BST_FORMAT_VERSION = 0
    """The plugin's YAML format version

    This should be set to ``1`` the first time any new configuration
    is understood by your :func:`~buildstream.plugin.Plugin.configure`
    implementation and subsequently bumped every time your
    configuration is enhanced.

    .. note::

       Plugins are expected to maintain backward compatibility
       in the format and configurations they expose. The versioning
       is intended to track availability of new features only.
    """

    def __init__(self, name, context, project, provenance, type_tag):

        self.name = name
        """The plugin name

        For elements, this is the project relative bst filename,
        for sources this is the owning element's name with a suffix
        indicating it's index on the owning element.

        For sources this is for display purposes only.
        """

        self.__context = context        # The Context object
        self.__project = project        # The Project object
        self.__provenance = provenance  # The Provenance information
        self.__type_tag = type_tag      # The type of plugin (element or source)
        self.__unique_id = _plugin_register(self)  # Unique ID
        self.__log = None               # The log handle when running a task

        # Infer the kind identifier
        modulename = type(self).__module__
        self.__kind = modulename.split('.')[-1]

        # Ugly special case to determine the minimum required version
        # from the project.
        if type_tag == 'element':
            version = project._element_format_versions.get(self.get_kind(), 0)
        else:
            version = project._source_format_versions.get(self.get_kind(), 0)

        # Raise PluginError on format version mismatch here
        if self.BST_FORMAT_VERSION < version:
            raise PluginError("{}: Format version {} is too old for requested version {}"
                              .format(self, self.BST_FORMAT_VERSION, version))

        self.debug("Created: {}".format(self))

    def __del__(self):
        # Dont send anything through the Message() pipeline at destruction time,
        # any subsequent lookup of plugin by unique id would raise KeyError.
        if self.__context.log_debug:
            print("DEBUG: Destroyed: {}".format(self))

    def __str__(self):
        return "{kind} {typetag} at {provenance}".format(
            kind=self.__kind,
            typetag=self.__type_tag,
            provenance=self.__provenance)

    def get_kind(self):
        """Fetches the kind of this plugin

        Returns:
           (str): The kind of this plugin
        """
        return self.__kind

    def node_items(self, node):
        """Iterate over a dictionary loaded from YAML

        Args:
            node (dict): The YAML loaded dictionary object

        Returns:
           list: List of key/value tuples to iterate over

        BuildStream holds some private data in dictionaries loaded from
        the YAML in order to preserve information to report in errors.

        This convenience function should be used instead of the dict.items()
        builtin function provided by python.
        """
        yield from _yaml.node_items(node)

    def node_provenance(self, node, member_name=None):
        """Gets the provenance for `node` and `member_name`

        This reports a string with file, line and column information suitable
        for reporting an error or warning.

        Args:
            node (dict): The YAML loaded dictionary object
            member_name (str): The name of the member to check, or None for the node itself

        Returns:
            (str): A string describing the provenance of the node and member
        """
        provenance = _yaml.node_get_provenance(node, key=member_name)
        return str(provenance)

    def node_get_member(self, node, expected_type, member_name, default=None):
        """Fetch the value of a node member, raising an error if the value is
        missing or incorrectly typed.

        Args:
           node (dict): A dictionary loaded from YAML
           expected_type (type): The expected type of the node member
           member_name (str): The name of the member to fetch
           default (expected_type): A value to return when *member_name* is not specified in *node*

        Returns:
           The value of *member_name* in *node*, otherwise *default*

        Raises:
           :class:`.LoadError`: When *member_name* is not found and no *default* was provided

        Note:
           Returned strings are stripped of leading and trailing whitespace

        **Example:**

        .. code:: python

          # Expect a string 'name' in 'node'
          name = self.node_get_member(node, str, 'name')

          # Fetch an optional integer
          level = self.node_get_member(node, int, 'level', -1)
        """
        return _yaml.node_get(node, expected_type, member_name, default_value=default)

    def node_validate(self, node, valid_keys):
        """This should be used in :func:`~buildstream.plugin.Plugin.configure`
        implementations to assert that users have only entered
        valid configuration keys.

        Args:
            node (dict): A dictionary loaded from YAML
            valid_keys (iterable): A list of valid keys for the node

        Raises:
            :class:`.LoadError`: When an invalid key is found

        **Example:**

        .. code:: python

          # Ensure our node only contains valid autotools config keys
          self.node_validate(node, [
              'configure-commands', 'build-commands',
              'install-commands', 'strip-commands'
          ])

        """
        _yaml.node_validate(node, valid_keys)

    def node_get_list_element(self, node, expected_type, member_name, indices):
        """Fetch the value of a list element from a node member, raising an error if the
        value is incorrectly typed.

        Args:
           node (dict): A dictionary loaded from YAML
           expected_type (type): The expected type of the node member
           member_name (str): The name of the member to fetch
           indices (list of int): List of indices to search, in case of nested lists

        Returns:
           The value of the list element in *member_name* at the specified *indices*

        Raises:
           :class:`.LoadError`

        Note:
           Returned strings are stripped of leading and trailing whitespace

        **Example:**

        .. code:: python

          # Fetch the list itself
          things = self.node_get_member(node, list, 'things')

          # Iterate over the list indices
          for i in range(len(things)):

              # Fetch dict things
              thing = self.node_get_list_element(
                  node, dict, 'things', [ i ])
        """
        return _yaml.node_get(node, expected_type, member_name, indices=indices)

    def configure(self, node):
        """Configure the Plugin from loaded configuration data

        Args:
           node (dict): The loaded configuration dictionary

        Raises:
           :class:`.SourceError`: If its a :class:`.Source` implementation
           :class:`.ElementError`: If its an :class:`.Element` implementation
           :class:`.LoadError`: If one of the *node* handling methods fail

        Plugin implementors should implement this method to read configuration
        data and store it. Use of the :func:`~buildstream.plugin.Plugin.node_get_member`
        convenience method will ensure that a nice :class:`.LoadError` is triggered
        whenever the YAML input configuration is faulty.

        Implementations may raise :class:`.SourceError` or :class:`.ElementError` for other errors.

        .. note::

           During configure, logging is suppressed unless buildstream is run with
           debugging output enabled.
        """
        raise ImplError("{tag} plugin '{kind}' does not implement configure()".format(
            tag=self.__type_tag, kind=self.get_kind()))

    def preflight(self):
        """Preflight Check

        Raises:
           :class:`.SourceError`: If its a :class:`.Source` implementation
           :class:`.ElementError`: If its an :class:`.Element` implementation
           :class:`.ProgramNotFoundError`: If a required host tool is not found

        This method is run after :func:`~buildstream.plugin.Plugin.configure` and
        after the pipeline is fully constructed. :class:`.Element` plugins are free
        to use the :func:`~buildstream.element.Element.dependencies` method and inspect
        public data at this time.

        Implementors should simply raise :class:`.SourceError` or :class:`.ElementError`
        with an informative message in the case that the host environment is
        unsuitable for operation.

        Plugins which require host tools (only sources usually) should obtain
        them with :func:`.utils.get_host_tool` which will raise
        :class:`.ProgramNotFoundError` automatically.
        """
        raise ImplError("{tag} plugin '{kind}' does not implement preflight()".format(
            tag=self.__type_tag, kind=self.get_kind()))

    def get_unique_key(self):
        """Return something which uniquely identifies the plugin input

        Returns:
           A string, list or dictionary which uniquely identifies the sources to use

        This is used to construct unique cache keys for elements and sources,
        sources should return something which uniquely identifies the payload,
        such as an sha256 sum of a tarball content. Elements should implement
        this by collecting any configurations which could possibly effect the
        output and return a dictionary of these settings.
        """
        raise ImplError("{tag} plugin '{kind}' does not implement get_unique_key()".format(
            tag=self.__type_tag, kind=self.get_kind()))

    def debug(self, brief, *, detail=None):
        """Print a debugging message

        Args:
           brief (str): The brief message
           detail (str): An optional detailed message, can be multiline output
        """
        if self.__context.log_debug:
            self.__message(MessageType.DEBUG, brief, detail=detail)

    def status(self, brief, *, detail=None):
        """Print a status message

        Args:
           brief (str): The brief message
           detail (str): An optional detailed message, can be multiline output

        Note: Status messages tell about what a plugin is currently doing
        """
        self.__message(MessageType.STATUS, brief, detail=detail)

    def info(self, brief, *, detail=None):
        """Print an informative message

        Args:
           brief (str): The brief message
           detail (str): An optional detailed message, can be multiline output

        Note: Informative messages tell the user something they might want
              to know, like if refreshing an element caused it to change.
        """
        self.__message(MessageType.INFO, brief, detail=detail)

    def warn(self, brief, *, detail=None):
        """Print a warning message

        Args:
           brief (str): The brief message
           detail (str): An optional detailed message, can be multiline output
        """
        self.__message(MessageType.WARN, brief, detail=detail)

    def log(self, brief, *, detail=None):
        """Log a message into the plugin's log file

        The message will not be shown in the master log at all (so it will not
        be displayed to the user on the console).

        Args:
           brief (str): The brief message
           detail (str): An optional detailed message, can be multiline output
        """
        self.__message(MessageType.LOG, brief, detail=detail)

    @contextmanager
    def timed_activity(self, activity_name, *, detail=None, silent_nested=False):
        """Context manager for performing timed activities in plugins

        Args:
           activity_name (str): The name of the activity
           detail (str): An optional detailed message, can be multiline output
           silent_nested (bool): If specified, nested messages will be silenced

        This function lets you perform timed tasks in your plugin,
        the core will take care of timing the duration of your
        task and printing start / fail / success messages.

        **Example**

        .. code:: python

          # Activity will be logged and timed
          with self.timed_activity("Mirroring {}".format(self.url)):

              # This will raise SourceError on its own
              self.call(... command which takes time ...)
        """
        with self.__context._timed_activity(activity_name,
                                            detail=detail,
                                            silent_nested=silent_nested):
            yield

    def call(self, *popenargs, fail=None, **kwargs):
        """A wrapper for subprocess.call()

        Args:
           popenargs (list): Popen() arguments
           fail (str): A message to display if the process returns
                       a non zero exit code
           rest_of_args (kwargs): Remaining arguments to subprocess.call()

        Returns:
           (int): The process exit code.

        Raises:
           (:class:`.PluginError`): If a non-zero return code is received and *fail* is specified

        Note: If *fail* is not specified, then the return value of subprocess.call()
              is returned even on error, and no exception is automatically raised.

        **Example**

        .. code:: python

          # Call some host tool
          self.tool = utils.get_host_tool('toolname')
          self.call(
              [self.tool, '--download-ponies', self.mirror_directory],
              "Failed to download ponies from {}".format(
                  self.mirror_directory))
        """
        exit_code, _ = self.__call(*popenargs, fail=fail, **kwargs)
        return exit_code

    def check_output(self, *popenargs, fail=None, **kwargs):
        """A wrapper for subprocess.check_output()

        Args:
           popenargs (list): Popen() arguments
           fail (str): A message to display if the process returns
                       a non zero exit code
           rest_of_args (kwargs): Remaining arguments to subprocess.call()

        Returns:
           (int): The process exit code
           (str): The process standard output

        Raises:
           (:class:`.PluginError`): If a non-zero return code is received and *fail* is specified

        Note: If *fail* is not specified, then the return value of subprocess.check_output()
              is returned even on error, and no exception is automatically raised.

        **Example**

        .. code:: python

          # Get the tool at preflight time
          self.tool = utils.get_host_tool('toolname')

          # Call the tool, automatically raise an error
          _, output = self.check_output(
              [self.tool, '--print-ponies'],
              "Failed to print the ponies in {}".format(
                  self.mirror_directory),
              cwd=self.mirror_directory)

          # Call the tool, inspect exit code
          exit_code, output = self.check_output(
              [self.tool, 'get-ref', tracking],
              cwd=self.mirror_directory)

          if exit_code == 128:
              return
          elif exit_code != 0:
              fmt = "{plugin}: Failed to get ref for tracking: {track}"
              raise SourceError(
                  fmt.format(plugin=self, track=tracking)) from e
        """
        return self.__call(*popenargs, collect_stdout=True, fail=fail, **kwargs)

    #############################################################
    #            Private Methods used in BuildStream            #
    #############################################################

    # _get_context()
    #
    # Fetches the invocation context
    #
    def _get_context(self):
        return self.__context

    # _get_project()
    #
    # Fetches the project object associated with this plugin
    #
    def _get_project(self):
        return self.__project

    # _get_unique_id():
    #
    # Fetch the plugin's unique identifier
    #
    def _get_unique_id(self):
        return self.__unique_id

    # _get_provenance():
    #
    # Fetch bst file, line and column of the entity
    #
    def _get_provenance(self):
        return self.__provenance

    # Accessor for logging handle
    #
    def _get_log_handle(self, log):
        return self.__log

    # Mutator for logging handle
    #
    def _set_log_handle(self, log):
        self.__log = log

    # Context manager for getting the open file handle to this
    # plugin's log. Used in the child context to add stuff to
    # a log.
    #
    @contextmanager
    def _output_file(self):
        if not self.__log:
            with open(os.devnull, "w") as output:
                yield output
        else:
            yield self.__log

    # _preflight():
    # Calls preflight() for the plugin, and allows generic preflight
    # checks to be added
    #
    # Raises:
    #    SourceError: If it's a Source implementation
    #    ElementError: If it's an Element implementation
    #    ProgramNotFoundError: If a required host tool is not found
    def _preflight(self):
        self.preflight()

    #############################################################
    #                     Local Private Methods                 #
    #############################################################

    # Internal subprocess implementation for the call() and check_output() APIs
    #
    def __call(self, *popenargs, collect_stdout=False, fail=None, **kwargs):

        with self._output_file() as output_file:
            if 'stdout' not in kwargs:
                kwargs['stdout'] = output_file
            if 'stderr' not in kwargs:
                kwargs['stderr'] = output_file
            if collect_stdout:
                kwargs['stdout'] = subprocess.PIPE

            self.__note_command(output_file, *popenargs, **kwargs)

            exit_code, output = utils._call(*popenargs, **kwargs)

            if fail and exit_code:
                raise PluginError("{plugin}: {message}".format(plugin=self, message=fail))

        return (exit_code, output)

    def __message(self, message_type, brief, **kwargs):
        message = Message(self.__unique_id, message_type, brief, **kwargs)
        self.__context._message(message)

    def __note_command(self, output, *popenargs, **kwargs):
        workdir = os.getcwd()
        if 'cwd' in kwargs:
            workdir = kwargs['cwd']
        command = " ".join(popenargs[0])
        output.write('Running host command {}: {}\n'.format(workdir, command))
        output.flush()
        self.status('Running host command', detail=command)

    def _get_full_name(self):
        project = self.__project
        if project._junction:
            return '{}:{}'.format(project._junction.name, self.name)
        else:
            return self.name


# Hold on to a lookup table by counter of all instantiated plugins.
# We use this to send the id back from child processes so we can lookup
# corresponding element/source in the master process.
#
# Use WeakValueDictionary() so the map we use to lookup objects does not
# keep the plugins alive after pipeline destruction.
#
# Note that Plugins can only be instantiated in the main process before
# scheduling tasks.
__PLUGINS_UNIQUE_ID = 0
__PLUGINS_TABLE = WeakValueDictionary()


# _plugin_lookup():
#
# Fetch a plugin in the current process by its
# unique identifier
#
# Args:
#    unique_id: The unique identifier as returned by
#               plugin._get_unique_id()
#
# Returns:
#    (Plugin): The plugin for the given ID, or None
#
def _plugin_lookup(unique_id):
    try:
        plugin = __PLUGINS_TABLE[unique_id]
    except (AttributeError, KeyError) as e:
        print("Could not find plugin with ID {}".format(unique_id))
        raise

    return plugin


# No need for unregister, WeakValueDictionary() will remove entries
# in itself when the referenced plugins are garbage collected.
def _plugin_register(plugin):
    global __PLUGINS_UNIQUE_ID                # pylint: disable=global-statement
    __PLUGINS_UNIQUE_ID += 1
    __PLUGINS_TABLE[__PLUGINS_UNIQUE_ID] = plugin
    return __PLUGINS_UNIQUE_ID