Python bindings for redis-ipc

A small python module implementing redis-ipc concepts.

redis-ipc is an example of how redis can be used as an advanced IPC mechanism on an embedded Linux system, for instance as a substitute for the more common choice of dbus.

redis-ipc is intended to make communication among different logical components of a system convenient. It is not intended to replace shared memory for high data-rate transfers between processes, where lowest possible overhead is key, but to provide a convenient and reliable way to implement the following IPC mechanisms:

• command queues
• settings
• status
• event channels

redis-ipc comes in 2 flavors, a python module (this repo) and a lightweight C library implementation. See the (original) redis-ipc C library repo for a more detailed description.

Quick Start Dev Environment

As there are not any Pypi packages available yet, you'll need to first clone this repository and then install locally (see below).

Note

All dependencies are optional except redis-py.

Dev Install

As long as you have git and at least Python 3.6, then the "easy" dev install is to clone this repository and install tox.

After cloning the repository, you can run the current tests with the tox command. It will build a virtual python environment for each installed version of python with all the python dependencies and run the tests (including style checkers and test coverage).

$ git clone https://github.com/VCTLabs/redis-ipc-py
$ cd redis-ipc-py
$ tox -e py<NN>-<platform>

where <NN> is your local version of python, and <platform> is one of either linux or macos, eg:

$ tox -e py38-linux

The above will run the default tox testenv, which includes the following:

• pre_test - install redis_ipc in tox env via pip and start the redis server
• test - run the simple msg bus send/receive tests with coverage
• post_test - stop the redis server

Important

The command above requires the installation of the full redis package (or at least redis-server). See the Usage Example below for install instructions; you can still run the other tox commands without a full redis install.

Other tox environment arguments you can pass include:

• tox -e build,check will build the python packages and run package checks
• tox -e style will run the flake8 and pycodestyle (PEP8) style checks
• tox -e lint will run pylint (somewhat less permissive than PEP8/flake8 checks)
• tox -e black will run the black formatter
• tox -e mypy will run mypy type checking

Standards and Coding Style

Black style and both pep8 and flake8 are part of the above test suite. There are also some CI pylint and bandit code analysis checks for complexity and security issues (we try to keep the "cognitive complexity" low when possible).

Usage Example

This repository contains a python module implementation of redis-ipc client/server classes, and requires redis-py and a running redis server for full functionality. The easiest way to get started is really just "Try it and see..." so you'll need to install and start a redis server first.

Using your system package manager, install the redis server package for your platform:

• on Gentoo: sudo emerge dev-db/redis dev-python/tox
• on Ubuntu: sudo apt-get install redis-server

• on CentOS:

  sudo yum install epel-release
  sudo yum update
  sudo yum install redis

On almost everything except Gentoo you should stop the system service before proceeding:

sudo systemctl stop redis

If your distro doesn't currently package tox, first complain (consider filing a "missing package" bug) and then use pip to install it into your usual python environment.

Testing With Tox

Once you have a redis-server installed, you can simply run the above tox command to manage the redis server component and run the tests for your local python version and OS platform, ie:

$ tox -e py38-cov-macos

The following section illustrates the (approximate) manual test steps run by the above command.

Developer Mode

To manually control redis-server and monitor the traffic on redis, use a workflow something like this. starting from the project source directory:

$ ./scripts/run_redis.sh start

Open another terminal window and start the monitor:

$ redis-cli -s /tmp/redis-ipc/socket monitor

From the first terminal window, run the (alternate) tests target:

$  tox -e tests

Observe both terminals; the tests should complete successfully with the test data cleared from redis, so executing the tests several times should all succeed. To manually clear all data from redis, simply stop and start the server:

$ ./scripts/run_redis.sh stop
$ ./scripts/run_redis.sh start

Manual Example Steps

From the repository directory, you should either add "." to your PYTHON_PATH or copy the python module to site-packages; for this example you can use the command shown below.

To start a local redis server first, run the following before you start the python interpreter:

$ mkdir /tmp/redis-ipc
$ redis-server --port 0 --pidfile /tmp/redis.pid --unixsocket /tmp/redis-ipc/socket --unixsocketperm 600 &
$ redis-cli -s /tmp/redis-ipc/socket config set save ""  # disable dump.rdb saving

The above command will use your local temp directory and permissions for the socket and PID files, and setting the port to zero disables listening on any network interfaces.

The above will also background the redis server, but you may need to hit <Enter> once to get the prompt back. Then type python in the source directory in 2 separate terminal windows and continue below.

For example, to run from the source directory, start a client process from the first terminal:

>>> import sys
>>> sys.path.append('.')
>>> from redis_ipc import RedisClient as rc
>>> myClient = rc("my_component")
>>> myClient.redis_ipc_send_and_receive("my_component", {}, 30)
{'timestamp': '1627166512.0108066', 'component': 'my_component', 'thread': 'main', 'tid': 24544, 'results_queue': 'queues.results.my_component.main', 'command_id': 'my_component:24544:1627166512.0108066'}

Then from a second terminal, start a server process:

>>> import sys
>>> sys.path.append('.')
>>> from redis_ipc import RedisServer as rs
>>> myServer = rs("my_component")
>>> result = myServer.redis_ipc_receive_command()
>>> myServer.redis_ipc_send_reply(result, result)

Note that client side of the above will block for the timeout period (30 sec in this example) while waiting for the other side to send/reply, so run the server commands in less than 30 sec. or increase the timeout value on the client.

If there is no running redis server, then you will get the following:

>>> import sys
>>> sys.path.append('.')
>>> from redis_ipc import RedisServer as rs
>>> myServer = rs("my_component")
>>> result = myServer.redis_ipc_receive_command()
Traceback (most recent call last):
...
redis.exceptions.ConnectionError: Error 2 connecting to unix socket: /tmp/redis-ipc/socket. No such file or directory.

When finished with the above, don't forget to kill the redis server:

$ cat /tmp/redis.pid | xargs kill

Testing | Troubleshooting

One of the great features of using redis for system-wide IPC is the ability to watch the interactions between components using the monitor command from redis-cli utility. Another great use is in unit testing of a single component, where a test script can push commands, update settings, check status and so forth. For both reasons it is useful to understand how each feature is implemented as redis data structures.

@@@TODO

Since redis-ipc requires the redis server to use a unix socket rather than tcp, remember to specify the socket path when running redis-cli :

redis-cli -s /tmp/redis-ipc/socket