python3-cyberfusion-queue-support

python3-cyberfusion-queue-support

Library to queue actions.

QueueSupport allows you to queue certain actions, such as restarting a service, unlinking a file, and much more.

For example, suppose the file /tmp/example.txt should be chmodded to 0600. You can queue the chmod:

>>> from cyberfusion.QueueSupport import Queue
>>> from cyberfusion.QueueSupport.items.chmod import ChmodItem
>>> queue = Queue()
>>> queue.add(ChmodItem(path="/tmp/example.txt", mode=0o600))

... see what the chmod would do with 'preview mode':

>>> queue.process(preview=False)
[<cyberfusion.QueueSupport.outcomes.ChmodItemModeChangeOutcome object at 0x7f947e8ef510>]
>>> print(queue.process(preview=True)[0])
Change mode of /tmp/example.txt from 0o644 to 0o600

... then actually run the chmod:

>>> print(queue.process(preview=False)[0])
Change mode of /tmp/example2.txt from 0o644 to 0o600

Install

PyPI

Run the following command to install the package from PyPI:

pip3 install python3-cyberfusion-queue-support

Then, run database migrations:

bin/queue-support-migrate

Debian

Run the following commands to build a Debian package:

mk-build-deps -i -t 'apt -o Debug::pkgProblemResolver=yes --no-install-recommends -y'
dpkg-buildpackage -us -uc

Configure

No configuration is supported.

Usage

Concepts

All project-specific terms are in italic.

After creating a queue, items can be added to it.

from cyberfusion.QueueSupport import Queue

queue = Queue()

item = ...

queue.add(item)

Items are of a certain type. Such as ChmodItem or SystemdUnitRestartItem. Items can have attributes, such as a path for an MkdirItem, or a unit name for SystemdUnitEnableItem.

from cyberfusion.QueueSupport.items.chmod import ChmodItem
from cyberfusion.QueueSupport.items.systemd_unit_enable import SystemdUnitEnableItem

item1 = ChmodItem(path="/tmp/example.txt", mode=0o600)
item2 = SystemdUnitEnableItem(name="httpd.service")

Each item type has one or multiple outcomes. These should come true for an item of that type to be completed. For example: for an item of type UnlinkItem, the outcome is that the file at the path given with the item is unlinked.

When a queue is processed, all the items added to it are fulfilled, meaning all the items' outcomes come true.

from cyberfusion.QueueSupport import Queue

from cyberfusion.QueueSupport.items.rmtree import RmTreeItem

item = RmTreeItem(path="/tmp/dir")

queue = Queue()

queue.add(item)

# Fulfill every item in the queue

queue.process(preview=False)
queue.process(preview=True)  # Only show what the outcomes would be

# Fulfill a single item

item.fulfill()

Diagram

graph TD;

  subgraph QueueSupport
    Queue["Queue"]
    Item["Add item"]
    Process["Process (fulfill all items)"]
  end

  Queue --> Item

  subgraph ItemTypes["Item types"]
    ChmodItem["ChmodItem"]
    SystemdUnitEnableItem["SystemdUnitEnableItem"]
    SystemdUnitRestartItem["SystemdUnitRestartItem"]
    MkdirItem["MkdirItem"]
    UnlinkItem["UnlinkItem"]
    RmTreeItem["RmTreeItem"]
    Other["Others..."]
  end

  Item --> ItemTypes
  ItemTypes --> Outcome["Outcome (item's goal)"]

  Process --> Fulfill["Fulfill outcomes for each item"]

  %% Example flows for item attributes and outcomes
  ChmodItem -.->|path, mode| Outcome
  SystemdUnitEnableItem -.->|unit name| Outcome
  MkdirItem -.->|path| Outcome
  UnlinkItem -.->|unlink file| Outcome
  RmTreeItem -.->|remove directory| Outcome

  Queue --> Process
  Process --> Fulfill

Example

from cyberfusion.QueueSupport import Queue
from cyberfusion.QueueSupport.items.chmod import ChmodItem

queue = Queue()

item = ChmodItem(path="/tmp/example.txt", mode=0o600)
print(item.outcomes)

queue.add(item)

preview = True or False

outcomes = queue.process(preview=preview)

for outcome in outcomes:
    print(str(outcome))