almanet 0.4.0

Web Messaging Protocol

almanet

Web Messaging Protocol is an open application level protocol that provides two messaging patterns:

• Routed Remote Procedure Calls (RPC)
• Produce & Consume

NSQ is a realtime distributed queue like message broker.

Almanet uses NSQ to exchange messages between different sessions.

Quick Start

Before install and run NSQD instance using this instruction.

Then install almanet PyPI package

pip install almanet

or

poetry add almanet

Create a new file and

import almanet

Create your own Microservice

Explanation of the code that defines and runs a simple microservice

Define your instance of microservice

example_service = almanet.new_service(
    "localhost:4150",
    prefix="net.example"
)

Arguments:

• the TCP addresses of the NSQ instances
• prefix for the service's procedures, helping in identifying and organizing them

Define your custom exception

class denied(almanet.rpc_error):
    """Custom RPC exception"""

This custom exception can be raised within procedures to signal specific error conditions to the caller.

Define your remote procedure to call

@example_service.procedure
async def greeting(
    session: almanet.Almanet,
    payload: str,
) -> str:
    """Procedure that returns greeting message"""
    if payload == "guest":
        raise denied()
    return f"Hello, {payload}!"

Decorator @example_service.procedure registers the greeting function as a remote procedure for the example_service.

Arguments:

• payload is a data that was passed during invocation.
• session is a joined service, instance of almanet.Almanet

It raises the custom denied exception, indicating that this payload is not allowed if payload is "guest". Otherwise, it returns a greeting message.

At the end of the file

if __name__ == "__main__":
    example_service.serve()

Starts the service, making it ready to handle incoming RPC requests.

Finally

Run your module using the python command

Call your Microservice

Explanation of the code for creating a new session, calling a remote procedure, and handling potential exceptions during the invocation.

Create a new session

session = almanet.new_session("localhost:4150")

Arguments:

• the TCP addresses of the NSQ instances

Calling the Remote Procedure

async with session:
    result = await session.call("net.example.greeting", "Aidar")
    print(result.payload)

async with session ensures that the session is properly managed and closed after use. Calls the remote procedure net.example.greeting with the payload "Aidar". Raises TimeoutError if procedure not found or request timed out. result.payload contains the result of the procedure execution.

Catching remote procedure exceptions

async with session:
    try:
        await session.call("net.example.greeting", "guest")
    except almanet.rpc_error as e:
        print("during call net.example.greeting('guest'):", e)

The try block attempts to call the net.example.greeting procedure with the payload "guest". If an exception occurs during the call, specifically an almanet.rpc_error, it is caught by the except block.

Finally

Run your module using the python command

See the full examples in ./examples directory.