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redisrpc

Lightweight RPC using Redis

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RedisRPC

by Nathan Farrington http://nathanfarrington.com <http://nathanfarrington.com>_

RedisRPC is the easiest to use RPC library in the world. (No small claim!) It has implementations in Ruby, PHP, and Python.

Introduction

Redis <http://redis.io/> is a powerful in-memory data structure server that is useful for building fast distributed systems. Redis implements message queue functionality with its use of list data structures and the LPOP, BLPOP, and RPUSH commands. RedisRPC implements a lightweight RPC mechanism using Redis message queues to temporarily hold RPC request and response messages. These messages are encoded as JSON <http://json.org/> strings for portability.

Many other RPC mechanisms are either programming language specific (e.g. Java RMI <https://en.wikipedia.org/wiki/Java_remote_method_invocation>) or require boiler-plate code for explicit typing (e.g. Thrift <https://en.wikipedia.org/wiki/Apache_Thrift>). RedisRPC was designed to be extremely easy to use by eliminating boiler-plate code while also being programming language neutral. High performance was not an initial goal of RedisRPC and other RPC libraries are likely to have better performance. Instead, RedisRPC has better programmer performance; it lets you get something working immediately.

Calculator Example

Each library implementation uses the same client and server example based off of a mutable calculator object. The clients and servers from different languages are interoperable.

.. figure:: http://github.com/nfarring/redisrpc/raw/master/docs/redisrpc_example.png :align: center :alt:

#. The client issues an RPC Request by using the Redis RPUSH command to push an RPC Request message into a Redis list called calc. #. The server retrieves the RPC Request message by using the Redis BLPOP command. #. The server dispatches the RPC Request to a local object, which in this case is a Calculator object. #. The server accepts the return value (or exception) from the Calculator object. #. The server issues an RPC Response by using the Redis RPUSH command to push an RPC Response message into a Redis list called calc:rpc:<RAND_STRING>, which was chosen by the client. #. The client retrieves the RPC Response message by using the Redis BLPOP command.

Note that the server or client can be made non-blocking by using the Redis LPOP command instead of BLPOP. I currently do not need this feature and have not added support for this, but patches are welcome.

That's all there is to it!

Ruby Usage

client.rb


::

    redis_server = Redis.new
    message_queue = 'calc'
    calculator = RedisRPC::Client.new redis_server, 'calc'
    calculator.clr
    calculator.add 5
    calculator.sub 3
    calculator.mul 4
    calculator.div 2
    assert calculator.val == 4

server.rb

::

redis_server = Redis.new
message_queue = 'calc'
local_object = Calculator.new
server = RedisRPC::Server.new redis_server, message_queue, local_object
server.run

PHP Usage

Note that the PHP library does not currently support named function arguments.

client.php


::

    $redis_server = new Predis\Client();
    $message_queue = 'calc';
    $calculator = new RedisRPC\Client($redis_server, $message_queue);
    $calculator->clr();
    $calculator->add(5);
    $calculator->sub(3);
    $calculator->mul(4);
    $calculator->div(2);
    assert($calculator->val() == 4);

server.php

::

$redis_server = new Predis\Client();
$message_queue = 'calc';
$local_object = new Calculator();
$server = new RedisRPC\Server($redis_server, $message_queue, $local_object);
$server->run();

Python Usage

client.py


::

    redis_server = redis.Redis()
    message_queue = 'calc'
    calculator = redisrpc.Client(redis_server, message_queue)
    calculator.clr()
    calculator.add(5)
    calculator.sub(3)
    calculator.mul(4)
    calcaultor.div(2)
    assert calculator.val() == 4

server.py

::

redis_server = redis.Redis()
message_queue = 'calc'
local_object = calc.Calculator()
server = redisrpc.Server(redis_server, message_queue, local_object)
server.run()

Installation

Ruby Installation


The `redis-rb <https://github.com/ezmobius/redis-rb>`_ library is
required. Install using RubyGems:

::

    gem install redisrpc

PHP Installation
~~~~~~~~~~~~~~~~

The `Predis <https://github.com/nrk/predis>`_ library is required.

The RedisRPC PHP library is available from
`Packagist <http://packagist.org/>`_ at:
`http://packagist.org/packages/nfarring/redisrpc <http://packagist.org/packages/nfarring/redisrpc>`_.
You can use `Composer <https://github.com/composer/composer>`_ to
install into your PHP project.

Python Installation

The redis-py <https://github.com/andymccurdy/redis-py>_ library is required.

The RedisRPC Python library is available from PyPI <http://pypi.python.org/> at: http://pypi.python.org/pypi/redisrpc <http://pypi.python.org/pypi/redisrpc>. You can install with pip <http://pypi.python.org/pypi/pip>_.

::

pip install redisrpc

Internal Message Formats

All RPC messages are JSON objects. User code will never see these objects because they are handled by the RedisRPC library.

RPC Request


An RPC Request contains two members: a ``function_call`` object and a
``response_queue`` string.

A ``function_call`` object has one required member: a ``name`` string
for the function name. It also has two optional members: (a) an ``args``
list for positional function arguments, and (b) a ``kwargs`` object for
named function arguments.

The ``response_queue`` string is the name of the Redis list where the
corresponding RPC Response message should be pushed by the server. This
queue is chosen programmatically by the client to be collision free in
the Redis namespace. Also, this queue is used only for a single RPC
Response message and is not reused for future RPC Response messages.

::

    { "function_call" : {
          "args" : [ 1, 2, 3 ],
          "kwargs" : { "a" : 4, "b" : 5, "c" : 6 },
          "name" : "foo"
        },
      "response_queue" : "calc:rpc:X7Y2US"
    }

RPC Response (Successful)

If an RPC is successful, then the RPC Response object will contain a single member, a return_value of some JSON type.

::

{ "return_value" : 4.0 }

RPC Response (Exception)


If an RPC encounters an exceptional condition, then the RPC Response
object will contain a single member, an ``exception`` string. Note that
the value of the ``exception`` string might not have any meaning to the
client since the client and server might be written in different
languages or the client might have no knowledge of the server's wrapped
object. Therefore the best course of action is probably to display the
``exception`` value to the user.

::

    { "exception" : "AttributeError(\\"\'Calculator\' object has no attribute \'foo\'\\",)" }

Source Code
-----------

Source code is available at
`http://github.com/nfarring/redisrpc <http://github.com/nfarring/redisrpc>`_.

License
-------

This software is available under the
`GPLv3 <http://www.gnu.org/licenses/gpl.html>`_ or later.

Changelog
---------

Version 0.3.4

-  Client now supports optional timeout.
-  Server now deletes message queue when starting.
-  PHP: Fixed exception handling.

Version 0.3.3

-  Ruby: Added a Ruby library implementation.

Version 0.3.2

-  Fixed some formatting in README.markdown that was causing problems
   when converted to reStructredText.
-  Added version information to README.markdown.
-  Added installation instructions to README.markdown.
-  Python: Added RPC message logging using the logging module.
-  Python: Added redis as an installation dependency.
-  Python: Now using Distribute instead of distutils.

Version 0.3.1

-  PHP: Changed composer.json predis dependency version.

Version 0.3.0

-  Empty function call args and kwargs are no longer transmitted.
-  PHP: Added support for the PHP language.
-  PHP: Now installable with PHP Composer.
-  Python: Shortened the Client and Server class names.
-  Python: Debugging modified to print JSON representation.
-  Python: Switched the README file back to ReStructred Text.

Version 0.2.1

-  Python: Fixed MANIFEST.in to reflect filename changes.

Version 0.2.0

-  Simplified the JSON RPC message format.
-  Documented the JSON RPC message format.
-  Python: Using HTML file for README, will it work?
-  Python: Renamed calc\_client to client.py.
-  Python: Renamed calc\_server to server.py.
-  Python: Added a RemoteException class, which can be raised by the
   client.

Version 0.1.2

-  Python: Fixed the download\_url in setup.py.
-  Python: Renamed the README file to README.rst to support browsing on
   Github.

Version 0.1.1

-  Python: Added README.
-  Python: Added long\_description to setup.py.
-  Python: Added MANIFEST.in file.
-  Python: Added examples/ subdirectory to MANIFEST.
-  Python: Modified examples/ directory to be consistent with README
   file.
-  Python: Fixed the download\_url in setup.py.

Version 0.1.0

-  Changed to the GPL license.
-  Python: Removed unused functionality from python/redisrpc.py.
-  Python: Added a setup.py installer script.

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