NFC Agent Python SDK

Python SDK for interacting with NFC readers via the nfc-agent local server.

Installation

pip install nfc-agent

Requirements

• Python 3.9+
• Running nfc-agent server

Quick Start

REST API (Simple Operations)

import asyncio
from nfc_agent import NFCClient

async def main():
    async with NFCClient() as client:
        # List readers
        readers = await client.get_readers()
        print(f"Found {len(readers)} reader(s)")

        # Read card
        try:
            card = await client.read_card(0)
            print(f"Card UID: {card.uid}")
            print(f"Card Type: {card.type}")
            if card.data:
                print(f"Data: {card.data}")
        except Exception as e:
            print(f"No card present: {e}")

asyncio.run(main())

Synchronous Usage

from nfc_agent import NFCClient

with NFCClient() as client:
    readers = client.get_readers_sync()
    card = client.read_card_sync(0)
    print(f"Card UID: {card.uid}")

WebSocket (Real-time Events)

import asyncio
from nfc_agent import NFCWebSocket

async def main():
    async with NFCWebSocket() as ws:
        # Subscribe to reader events
        await ws.subscribe(0)

        @ws.on_card_detected
        def handle_card(event):
            print(f"Card detected: {event.card.uid}")

        @ws.on_card_removed
        def handle_removed(event):
            print(f"Card removed from reader {event.reader}")

        # Keep running
        await asyncio.sleep(60)

asyncio.run(main())

Card Polling

import asyncio
from nfc_agent import NFCClient

async def main():
    async with NFCClient() as client:
        poller = client.poll_card(0, interval=0.5)

        @poller.on_card
        def handle_card(card):
            print(f"Card: {card.uid}")

        @poller.on_removed
        def handle_removed():
            print("Card removed")

        await poller.start()
        await asyncio.sleep(30)
        poller.stop()

asyncio.run(main())

API Reference

NFCClient

REST API client for simple request/response operations.

from nfc_agent import NFCClient

# With context manager (recommended)
async with NFCClient(base_url="http://127.0.0.1:32145", timeout=5.0) as client:
    ...

# Or sync
with NFCClient() as client:
    ...

Methods

MIFARE Classic

MIFARE Ultralight / NTAG

NFCWebSocket

WebSocket client for real-time communication and events.

from nfc_agent import NFCWebSocket

async with NFCWebSocket(
    url="ws://127.0.0.1:32145/v1/ws",
    timeout=5.0,
    auto_reconnect=True,
    reconnect_interval=3.0,
    secure=False  # Use wss:// for HTTPS pages
) as ws:
    ...

Methods

All methods from NFCClient, plus:

DESFire Transparent Session

Events

@ws.on_card_detected
def handle_card(event):
    print(event.card.uid)

@ws.on_card_data
def handle_data(event):
    # event.pages (NTAG) or event.blocks (MIFARE Classic)
    print(event.pages)

@ws.on_card_removed
def handle_removed(event):
    print(f"Removed from reader {event.reader}")

@ws.on_readers_changed
def handle_readers(event):
    # Fired when readers are plugged in/removed, or pcscd becomes available
    # after startup. event.readers is the full current reader list.
    print(f"Readers now connected: {event.readers}")

@ws.on_connected
def handle_connected():
    print("Connected")

@ws.on_disconnected
def handle_disconnected():
    print("Disconnected")

@ws.on_error
def handle_error(error):
    print(f"Error: {error}")

CardPoller

Polls a reader for card presence.

poller = client.poll_card(reader_index, interval=1.0)

@poller.on_card
def handle_card(card):
    print(card.uid)

@poller.on_removed
def handle_removed():
    print("Removed")

@poller.on_error
def handle_error(e):
    print(f"Error: {e}")

await poller.start()
# ...
poller.stop()

Types

from nfc_agent import (
    Reader,
    Card,
    CardDataType,
    VersionInfo,
    HealthInfo,
    CardDetectedEvent,
    CardRemovedEvent,
    MifareKeyType,
    MifareBlockData,
    UltralightPageData,
    NDEFRecord,
)

Exceptions

from nfc_agent import (
    NFCAgentError,    # Base exception
    ConnectionError,  # Connection failed
    CardError,        # Card operation failed
    DesfireError,     # DESFire session failed (subclass of CardError, optional .status_code)
    APIError,         # API returned error
    TimeoutError,     # Request timed out
    ReaderError,      # Reader issue
)

Examples

Write URL to Card

async with NFCClient() as client:
    await client.write_card(0, data="https://example.com", data_type="url")

Write Text to Card

async with NFCClient() as client:
    await client.write_card(0, data="Hello World", data_type="text")

Write JSON to Card

import json

async with NFCClient() as client:
    data = json.dumps({"user_id": 123, "name": "Alice"})
    await client.write_card(0, data=data, data_type="json")

Read MIFARE Classic Block

from nfc_agent import MifareKeyType

async with NFCClient() as client:
    block = await client.read_mifare_block(
        0,
        block=4,
        key="FFFFFFFFFFFF",
        key_type=MifareKeyType.A
    )
    print(f"Block {block.block}: {block.data}")

DESFire Transparent Session

For DESFire EV2/EV3 cards, the SDK exposes a transparent APDU session (WebSocket only — there is no REST equivalent). The agent holds the card connection open across messages so an external party — typically the SimplyPrint backend, which keeps the DESFire keys in its HSM — can drive an interactive AuthenticateEV2First handshake (a 3-pass challenge/response that can't be pre-computed) and the secure-messaging commands that follow.

The agent performs no DESFire cryptography and holds no keys. Your code sends raw APDU bytes and gets the card's raw response (including the status word) back; all session secrets stay on your side. Send native DESFire APDUs (CLA=0x90) — the real commands come from the backend. Don't subscribe a reader while a session is open on it (unsubscribe first), and note sessions are dropped automatically on disconnect. Recommended readers are the ACR1252U / ACR1552U class.

from nfc_agent import NFCWebSocket, DesfireError

async with NFCWebSocket() as ws:
    # Open the session — agent keeps the card connection open across calls
    session = await ws.open_desfire_session(0)
    print(f"UID: {session.uid}  ATR: {session.atr}")

    try:
        # Transmit one APDU. Use single transmits for the interactive auth handshake.
        # (Here: the get-UID pseudo-APDU, answered by any ISO 14443-A card.)
        resp = await ws.desfire_transmit(0, apdu="ffca000000")
        print(resp.response, hex(resp.sw1), hex(resp.sw2))  # full reply incl. status word

        # Batch transmit for non-interactive stretches
        batch = await ws.desfire_transmit_batch(0, apdus=["ffca000000", "ffca000000"])
        for r in batch.responses:
            print(r.response, hex(r.sw1), hex(r.sw2))
    except DesfireError as e:
        print(f"DESFire error: {e}  status={e.status_code}")
    finally:
        await ws.close_desfire_session(0)

apdu and response are hex strings; response includes the trailing status word. Failures raise DesfireError (a subclass of CardError) with an optional status_code. See scripts/test_desfire_session.py for a card-agnostic smoke test.

Monitor Multiple Readers

async with NFCWebSocket() as ws:
    # Subscribe to all readers
    readers = await ws.get_readers()
    for i, reader in enumerate(readers):
        await ws.subscribe(i)
        print(f"Subscribed to {reader.name}")

    @ws.on_card_detected
    def handle(event):
        print(f"Reader {event.reader}: {event.card.uid}")

    await asyncio.sleep(300)

Development

# Install dev dependencies
pip install -e ".[dev]"

# Run tests
pytest

# Lint
ruff check src tests

# Type check
mypy src

License

MIT