LAPLACE Server (LAPLACE-LHC)

ZMQ-based server for the LAPLACE-LHC project.

This package provides a lightweight, command-driven server running in its own thread, designed to exchange structured messages with clients using a defined protocol. It is independent from GUI frameworks, while still allowing seamless integration with PyQt through callback-based controllers.

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Features

• ZMQ-based TCP server
• Runs in its own non-daemon thread
• Protocol-based message validation and dispatching
• Configurable command callbacks
• Optional PyQt6 signal integration (without QObject inheritance)
• Clear separation between protocol, validation, and handlers

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Installation

From PyPI:

pip install laplace-server

Or from source (editable mode):

git clone https://github.com/SemionTche/laplace_server.git
cd laplace_server
pip install -e .

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Basic Usage

Start a server

from laplace_server.server_lhc import ServerLHC
from laplace_server.protocol import DEVICE_MOTOR

server = ServerLHC(
    name="my_server",
    address="tcp://*:5555",
    freedom=2,
    device=DEVICE_MOTOR
)

server.start()

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Update server data

server.set_data({"x": 1.2, "y": 3.4})

The stored data is transmitted when a CMD_GET request is received.

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Stop the server

server.stop()

⚠️ The server runs in its own non-daemon thread and must be explicitly stopped to allow the Python process to exit cleanly.

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Protocol Overview

The server communicates using a lightweight, JSON-based message protocol over ZMQ. Each message must follow a well-defined structure and include a protocol version to ensure compatibility between clients and servers.

Message Structure

All messages exchanged with the server must be JSON objects with the following fields:

• version — Protocol version identifier
• cmd — Command name
• from — Sender identifier
• payload — Command-specific data (may be empty)

Example message:

{
  "version": "0.1.6",
  "cmd": "GET",
  "from": "client_1",
  "payload": {}
}

Messages that do not comply with this structure are rejected and may trigger an error response from the server.

Commands

The protocol defines a fixed set of commands used to interact with the server, including:

• CMD_INFO — Request server information
• CMD_PING — Check server availability
• CMD_GET — Retrieve the server data
• CMD_SET — For motor realted server, set new positions
• CMD_SAVE — Indicate a saving path
• CMD_OPT — Send optimization-related data
• CMD_STOP — Request server shutdown

Each command is handled by a dedicated handler function on the server side.

Protocol Versioning

The protocol version is defined by laplace_server.protocol.PROTOCOL_VERSION and is validated for every incoming message. If a version mismatch is detected, the message is rejected to prevent undefined behavior.

The protocol version is independent from the package release version (__version__) and is only updated when the message format or semantics change.

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PyQt6 Integration

The server does not inherit from QObject. Instead, callbacks can be connected to a ServerController, which emits PyQt6 signals.

from laplace_server.server_lhc import ServerLHC
from laplace_server.server_controller import ServerController

server = ServerLHC(...)
controller = ServerController()

server.set_on_get(controller.on_get)
server.set_on_opt(controller.on_opt)

This design keeps the server independent from PyQt while remaining GUI-friendly.

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Project Structure

laplace_server/
├── server_lhc.py         # Main server implementation
├── server_controller.py  # PyQt6 signal controller (optional)
├── protocol.py           # Protocol constants and helpers
├── validations.py        # Input and message validation utilities
├── handlers/             # Command handlers
└── __init__.py

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Versioning

• laplace_server.__version__ Package release version (matches the PyPI version).

• laplace_server..protocol.PROTOCOL_VERSION Internal communication protocol version, used to validate messages and ensure compatibility between clients and servers.

These two versions are intentionally independent.

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Error Handling Philosophy

• Validation functions return human-readable error messages or None
• Errors are logged, not raised, for expected runtime issues
• The server decides how to react (reply with error, ignore, continue)

This approach is suited for long-running network services.

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License

GPL-3.0

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Status

This project is actively used within the LAPLACE-LHC ecosystem and is intended for controlled environments rather than general-purpose networking.