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Reverse Engineering an NFC Protocol

Last week, I purchased a fun toy: a 4.2-inch e-Paper display that works without a battery and can be updated via an NFC wireless signal from a mobile app.

The problem, however, is the app. The manufacturer provides iOS, Android, and PC applications, but the UI is poorly designed and does not allow raw image uploads. Instead, images are always dithered by the app, which significantly reduces display quality.

So, I decided to reverse engineer the NFC protocol and re-implement the app — and that was completed in a day, with the help of an “AI agent.”

Beginning

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NFC で書き換えられる電子ペーパーのプロトコル

いま巷で話題の NFC で書き換えできる名札サイズの電子ペーパーのプロトコルを調べました。 @alt-coreさんの追加の調査も参考にしています。

実装

• Swift EPaperNFCSwift (@niw)
• Python nfc-eink (@alt-core)

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#!/usr/bin/env python3
"""
Apply Atkinson dithering to an input PNG using a fixed 4-color palette:
red, yellow, black, and white.
"""

from __future__ import annotations

import argparse
from pathlib import Path

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Unsafe Binding Access on SwiftUI

It’s not always safe to access a Binding within a callback that isn’t part of SwiftUI’s event system. An example is illustrated in the following sample code:

extension Notification.Name {
    static let event = Notification.Name("event")
}

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//
//  RunOnMainRunLoopExitScheduler.swift
//  RunOnMainRunLoopExitScheduler
//
//  Created by Yoshimasa Niwa on 11/5/25.
//

import Combine
import Foundation

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# Copy files to the "documents" folder by using MTP.
# Mostly for sending documents locally to recent Kindle devices.
#
# Usage: python3 copy_to_documents.py [file ...]
#
# Requires `aftl` package that can be installed from a non-master branch at
# <https://github.com/niw/android-file-transfer-linux>.
#
# Copyright (c) 2025 Yoshimasa Niwa
#

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//
//  Tuple.swift
//  Tuple
//
//  Created by Yoshimasa Niwa on 8/8/25.
//

public struct Tuple<each T: Equatable>: Equatable {
    public static func == (lhs: Tuple<repeat each T>, rhs: Tuple<repeat each T>) -> Bool {
        var result = true

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#!/bin/bash

# Congratulations! You found the easter egg! ❤️
# おめでとうございます！隠されたサプライズを見つけました！❤️

# Define the text to animate
text="♥PEACE♥FOR♥ALL♥PEACE♥FOR♥ALL♥PEACE♥FOR♥ALL♥PEACE♥FOR♥ALL♥PEACE♥FOR♥ALL♥"

# Get terminal dimensions
cols=$(tput cols)

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//
//  UUIDv7.swift
//  UUIDv7
//
//  Created by Yoshimasa Niwa on 7/25/25.
//

import Foundation
import Security

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import Foundation

public enum ChunkedDataTaskError: Swift.Error {
    case notSuccess(_ data: Data, _ httpResponse: HTTPURLResponse)
}

private extension Int {
    var isSuccess: Bool {
        (200 ..< 300).contains(self)