lnc-client 0.1.1

Python client for the Lance Wire Protocol (LWP) — high-performance, low-latency data streaming

lnc-client

Python client for the Lance Wire Protocol (LWP) — high-performance, low-latency data streaming.

Lance is an io_uring-based streaming server designed to saturate 100G NICs with minimal latency. This client implements the full LWP binary protocol for Python applications.

Installation

pip install lnc-client

Requirements: Python 3.10+

Quick Start

Producer

import asyncio
from lnc_client import Producer, ProducerConfig

async def main():
    producer = await Producer.connect("localhost:1992", ProducerConfig())

    # Send with ACK (guaranteed delivery)
    batch_id = await producer.send(topic_id=1, data=b'{"price": 6942.25}')

    # Send without waiting for ACK (pipelined, higher throughput)
    batch_id = await producer.send_async(topic_id=1, data=b'fire and forget')

    await producer.close()

asyncio.run(main())

Consumer

import asyncio
from lnc_client import StandaloneConsumer, StandaloneConfig

async def main():
    consumer = await StandaloneConsumer.connect(
        "localhost:1992",
        StandaloneConfig(consumer_name="my-app", topic_id=1),
    )

    while True:
        result = await consumer.poll()
        if result is None:
            await asyncio.sleep(0.05)
            continue

        for record in result.records:
            print(f"Type={record.record_type}, Data={record.value}")

        print(f"Lag: {result.lag} bytes")

asyncio.run(main())

Topic Management

import asyncio
from lnc_client import LanceClient, ClientConfig

async def main():
    async with LanceClient(ClientConfig(host="localhost")) as client:
        topics = await client.list_topics()

        topic = await client.create_topic("my-events")

        # Create with retention (7-day, 1GB max)
        topic = await client.create_topic_with_retention(
            "logs", max_age_secs=7*86400, max_bytes=1024**3
        )

        await client.set_retention(topic["id"], max_age_secs=86400)

asyncio.run(main())

Configuration

ProducerConfig

Option	Default	Description
batch_size	32768	Max batch size in bytes
linger_ms	5	Max wait before sending partial batch
compression	False	Enable LZ4 compression
max_pending_acks	64	Max unacknowledged batches

StandaloneConfig

Option	Default	Description
consumer_name	""	Consumer identifier
topic_id	0	Topic to consume from
max_fetch_bytes	65536	Max bytes per fetch
start_offset	0	Initial byte offset
poll_interval_ms	50	Polling interval when idle

ClientConfig

Option	Default	Description
host	"localhost"	Lance server hostname
port	1992	Lance server port

TLV Record Types

Records use Type-Length-Value encoding:

Type	Code	Description
RawData	0x01	Unstructured binary
JSON	0x02	JSON-encoded record
MessagePack	0x03	MessagePack-encoded
KeyValue	0x10	Key-value pair
Timestamped	0x11	Timestamp + data
Null	0xFF	Tombstone/empty

Error Handling

from lnc_client import (
    LanceError,
    ConnectionError,
    BackpressureError,
    TopicNotFoundError,
    InvalidFrameError,
)

try:
    await producer.send(topic_id=99, data=b"test")
except TopicNotFoundError:
    print("Topic doesn't exist")
except BackpressureError:
    print("Server is overloaded, slow down")
except ConnectionError:
    print("Connection lost")

Protocol Details

This client implements the Lance Wire Protocol (LWP) v1.0:

• 44-byte fixed header with CRC32C validation
• Hardware-accelerated checksums (SSE4.2 / ARM CRC)
• Backpressure signaling from server
• Keepalive with 30-second timeout
• Batched production with ACK tracking
• Offset-based consumption with seek/rewind
• LZ4 compression (optional, per-batch)
• Reconnection with exponential backoff (100ms base, 30s max, jitter)

Development

git clone https://github.com/nitecon/lnc-client-py.git
cd lnc-client-py
python3 -m venv .venv
source .venv/bin/activate
pip install -e ".[dev]"
pytest -v

39 tests covering protocol parsing, CRC32C validation, TLV encoding/decoding, and frame builders.

License

MIT