Tuesday, July 15, 2025

How to write a software issue

If a software problem report or issue describes a large goal or vision, it should be documented as part of a concept of operations or a specification. If you can’t write clear acceptance criteria, or if a developer can’t reasonably complete it in 1–3 working days, it’s probably too big and needs to be split.

Large issues often depend on knowledge of many parts of the system, while smaller ones usually touch just one area. Smaller issues are easier to test, review, and merge. A smaller scope also makes it easier to prioritize and adjust based on feedback. 

Smaller, well-defined tasks are much better candidates as a “first issue” for a newcomer because they feel more approachable. It’s also much clearer when the work is done and what the expected result is. A newcomer can complete the work, submit a pull request, and get feedback quickly — which builds confidence and keeps them engaged.

Monday, June 2, 2025

Non-Functional Requirements

When building software, we define two types of requirements:

  1. Functional: What the system should do (e.g., login, payment).
  2. Non-functional: How well it should do it (e.g., speed, copy protection, security, scalability).

Without this distinction, you risk neglecting important aspects of system quality that don’t show up in features alone. You can implement a feature that works but still fails the user if it’s slow, insecure, or unreliable. Performance is considered non-functional because it affects user experience but doesn’t define what the system does.

It is similar to the frontend-backend layers but not exactly. Frontend-backend is about where things happen. Functional vs. non-functional is about what vs. how well. But there's overlap — non-functional requirements often live in the backend, yet both layers can have them.

In the beginning of a project, non-functional requirements are often forgotten because

  1. They’re abstract and harder to measure
  2. Not visible in UI

But ignoring them leads to rework, failure at scale, and unhappy users. Functional requirements get you a working, minimum viable product. Non-functional requirements make it usable, scalable, and successful.

Wednesday, May 21, 2025

In PHP, "false" can be true

All values loaded from an environment (.env) file using vlucas/phpdotenv are treated as strings, regardless of how they appear in the file. Even if your .env file contains IS_IN_SANDBOX_MODE = false, $_ENV['IS_IN_SANDBOX_MODE'] will be "false". The following condition would evaluate to true, even though the variable in the .env file is set to false, because "false" is a non-empty string and thus truthy in PHP:

if (IS_IN_SANDBOX_MODE) --> if ("false") --> true

This is a common gotcha when working with environment variables in PHP. To address this, you can use:

define('IS_IN_SANDBOX_MODE', filter_var($_ENV['IS_IN_SANDBOX_MODE'],
    FILTER_VALIDATE_BOOLEAN));

Note that FILTER_VALIDATE_BOOLEAN will return null for values like "True", "FALSE", "TRUE", etc. if (null) evaluates to false. It will return true for "true" (lowercase), "1", "on", or "yes". It will return false for "false" (lowercase), "0", "off", "no", or an empty string "".

Alternatively, my personal preference (because it makes the string conversion explicit):

define('IS_IN_SANDBOX_MODE', $_ENV['IS_IN_SANDBOX_MODE'] === 'true');

Or, when using it in a condition:

if (IS_IN_SANDBOX_MODE === 'true')

Wednesday, May 7, 2025

React Native Parameter Passing

When building mobile apps with React Native, we often face a decision about how to pass data between components - especially to screen components. Let's examine two common approaches and when to use each:

1. Direct Props Passing:

interface AddressInfoProps {
    cartItems: CartItem[];
    discountPrice: number;
}
const AddressInfo: React.FC<AddressInfoProps> = ({ cartItems, discountPrice }) => {
    // Component implementation
};

2. Navigation Route Parameters:

import { useRoute, RouteProp } from '@react-navigation/native';
type AddressInfoRouteProp = RouteProp<{
    AddressInfo: {
        cartItems: CartItem[];
        discountPrice: number;
    };
}, 'AddressInfo'>;
const AddressInfo: React.FC = () => {
    const route = useRoute<AddressInfoRouteProp>();
    const { cartItems, discountPrice } = route.params;
    // Component implementation
};

Option 1 is simpler, but it lacks built-in mechanisms to persist state when navigating back and forth between screens. You must always explicitly pass the parameters, meaning the developer is responsible for state persistence. Use it when the component is part of a larger component hierarchy where the parent already has the necessary data to pass down.

Use route parameters (Option 2) when the component represents a screen in your navigation flow—i.e., when backward and forward navigation is expected. With Option 2, the React Native navigation system handles state automatically. If the user navigates to another page and then presses the back button, the screen will re-render with its previous state.

Other options:

Context API: Best for data needed by many components at different nesting levels, but avoid for frequently changing data as it can cause unnecessary re-renders

State Management Libraries (Redux, MobX, Zustand, Jotai): Best for complex applications with lots of shared state and interactions between different parts of the app

URL Parameters: Best for web applications where maintaining bookmarkable state is important

Local Storage: Best for persisting data between app sessions like login status

Monday, May 5, 2025

Storing auth tokens on mobile

React Native AsyncStorage is a simple key-value storage system that saves data as plain text. This means that anyone with access to the device or its backups can potentially read your auth tokens, API keys, or other sensitive data if you use AsyncStorage.

Storing sensitive data unencrypted can also violate Google Play and AppStore guidelines which might result in your app being rejected. Reviewers might run basic security tests that could expose unencrypted token storage.

SecureStore is Expo's abstraction layer that leverages the native security infrastructure of both iOS and Android platforms. SecureStore automatically encrypts all data before storage and provides a unified API that works identically on both iOS and Android. While SecureStore has slightly more overhead due to encryption/decryption operations, the performance impact is negligible for typical use cases like token storage. The security benefits far outweigh any minor performance considerations.

Wednesday, March 5, 2025

Converting a web app to mobile

If you have a responsive web app, you could convert it to a mobile app using React Native WebView without writing any additional mobile code. However, there may be challenges with getting approval from both Google Play and the Apple App Store when using a WebView wrapper approach:
  1. Apple App Review Guidelines Rule 4.2 explicitly states that apps should include features, content, and UI elements that elevate them beyond being just a repackaged website.
  2. Google Play Store: While generally more lenient than Apple, Google still requires apps to provide a reasonably engaging user experience.
The more native integration you include, the more likely you are to pass the review process. Potential Solutions:
  1. Add native functionality such as push notifications or device camera integration.
  2. Implement offline capabilities that aren't available in the web version.
The easiest way to convert your web app to mobile is to ask claude.ai to do it. Your job would be to review, refactor, test and debug the generated mobile code.

Monday, February 10, 2025

Memory cost of image conversion

In my web app, users can upload images as PNG, JPEG etc. I convert them to WebP because it uses much less space on disk and loads faster in web page requests. However, conversion uses raw pixels, so the memory (RAM) required is almost irrelevant to the original file size because file size depends on the compression of raw pixels. The memory needed is primarily determined by: Width * Height * Bytes per pixel. 

A PNG needs 3 bytes for RGB and 1 byte for alpha = 4 bytes per pixel. For a 5637x5637 PNG with RGBA colors, we need 5637 * 5637 * 4 bytes per pixel = ~127MB just for the uncompressed pixel data alone. The file size of that PNG is 6MB.

JPEG files typically don't have an alpha channel, so they need 3 bytes per pixel. For a 5637x5637 JPEG, memory needed would be 5637 * 5637 * 3 = ~95MB. The actual file size of the JPEG could range from:

  • High quality (90%): 2-8MB
  • Medium quality (70%): 1-4MB
  • Low quality (50%): 500KB-2MB
When setting upload limits for image processing, you should primarily consider the image dimensions (megapixels) rather than the file size (megabytes). Here's why:

  1. A user could upload a highly compressed 2MB PNG that's 10000x10000 pixels - this would need ~400MB RAM to process.
  2. Another user could upload a poorly compressed 10MB JPEG that's 1000x1000 pixels - this would only need ~3MB RAM to process.

Considering that current mobile cameras can typically capture 16MP images, the decompressed image would require approximately 16e6 pixels × 4 bytes/pixel / 1024 / 1024 = 61MB of memory. Additional couple of MB memory may be needed as a buffer for libraries like PHP GD, which might use it for copying bytes. 

Here are details from my web app of processing a 16MP JPEG with GD functions (total 172MB, calculated with memory_get_peak_usage):

  • imagecreatefromjpeg: +68MB
  • imagewebp: 130MB (+62MB)
  • resizeWebP:
    • imagecreatefromwebp: 140MB (+10MB)
    • imagecreatetruecolor: 156MB (+16MB)
    • imagewebp: 172MB (+16MB)

To be safe, allocating 200MB of memory would be prudent. If your server has 3GB total RAM, it means that your web app can handle at most 3GB/200MB ≈ 15 concurrent image conversions.

Converting images to WebP saves disk space and speeds up the web app in the long run, but it consumes a lot of RAM in the short run.