netwatch/README.md at feat/viewport-harness

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test: automated responsive-layout harness (closes #13 )

Verifies the mobile layout from #5 with a real browser engine instead of
by hand on a phone. make frontend-viewport-test builds dist/, serves it
from the same digest-pinned nginx image and the same nginx.conf the
shipping container uses, and drives a digest-pinned headless Chrome
against it over CDP.

Viewport widths are derived from the app's own CSS rather than from a
list of phone models: the @media conditions in src/styles.css and any
Tailwind responsive prefixes in the markup are parsed, and each
breakpoint is tested one pixel below, exactly on, and one pixel above.
max-width: 768px matches at 768, and a generic 375px test sails past
that boundary entirely. Four anchor viewports are added with stated
reasons: a 320px floor, a desktop baseline, and two phone-landscape
sizes straddling the breakpoint.

Assertions are on computed layout, not screenshots: horizontal overflow,
elements past the viewport edge, clipped text (deliberate ellipsis
truncation excluded), 44x44 minimum tap targets, and genuine reflow of
the host rows checked on both flex-direction and geometry. Probing and
gateway detection are asserted to still run at narrow widths, since the
early-return mobile path rejected in #8 is what would silently regress.
Screenshots are written to tmp/viewport/ as artifacts alongside the
results, not as the evidence.

puppeteer-core rather than playwright: it is the one variant of either
that never downloads or bundles a browser, so the browser stays a
digest-pinned image and the npm side is pinned by yarn.lock integrity.

The browser container runs on an --internal docker network with no route
off the host; the harness answers the app's latency probes itself from a
fixed delay table so the rows render a realistic spread of value widths.

Kept out of make check: it needs Docker and takes minutes, where make
test has to stay under 20 seconds.

Every check guards its own presence, so none can pass against a page it
is not measuring. The tap-target check in particular would otherwise be
inert: an empty undersized set means both "all controls are big enough"
and "the selectors have gone stale", and the size comparison alone
cannot tell those apart. Each selector therefore declares the minimum
number of visible instances the page must contain, per selector rather
than in total, so one stale selector out of four fails rather than only
all four at once.

Layout expectation is likewise refused rather than guessed. A width is
narrow when a max-width block matches (desktop-first, what the app does
today) or, for a min-width-only mobile-first set, when it falls below
every breakpoint; a set mixing both cannot be resolved from the
conditions alone, because which block owns the reflow is a property of
the rules inside it, so the run fails with an explanation instead of
testing the right widths against the wrong expectation.

The harness was observed failing before being trusted, four times: a
planted 900px fixed-width element in a host row; the mobile reflow rule
neutered; the tap-target threshold lowered so nothing was undersized and
.pin-btn then renamed, which took the check from 8/8 green at every
touch viewport to failing at all six, naming the stale selector; and a
second media block added so the breakpoint set mixed max and min, which
aborted the run. All reverted.

Against the current layout it reports two real defects, filed as #42
(horizontal overflow at 320px) and #43 (tap targets below 44x44).

2026-08-09 15:22:54 +00:00

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NetWatch is an MIT-licensed JavaScript single-page application by @sneak that provides real-time network latency monitoring to common internet hosts, displayed with color-coded figures and sparkline graphs, served from a static bucket or Docker container.

Getting Started

# Install dependencies
yarn install

# Development server
yarn dev

# Production build
yarn build

# Preview production build
yarn preview

# Docker
docker build -t netwatch .
docker run -p 8080:8080 netwatch

Entrypoints

This repository adheres to the Scripts to Rule Them All standard: normalized scripts in script/ are the entrypoints for the development workflow, and the Makefile targets are thin shims that call them. We provide:

script/bootstrap — install all dependencies (pinned node via nvm if needed, yarn via corepack, yarn install --frozen-lockfile)
script/setup — make a fresh clone ready for development: bootstrap plus the git pre-commit hook
script/projectname — print the project name (used for the Docker image tag)
script/test — run the production build as the test (no unit tests yet)
script/lint — run prettier in check mode
script/fmt — format all files (writes)
script/fmt-check — check formatting (read-only)
script/check — run test, lint, and fmt-check
script/frontend-viewport-test — responsive-layout verification of the built frontend in a containerised headless Chrome (see test/viewport/README.md). Not part of script/check: it needs Docker and takes minutes.
script/docker — build the Docker image tagged via script/projectname
script/cibuild — CI entrypoint: plain docker build .
script/precommit — run by the git pre-commit hook; runs script/check
script/install-precommit — install the git pre-commit hook

Responsive layout

The narrow-viewport layout lives in the max-width: 768px media block in src/styles.css. It is verified automatically by make frontend-viewport-test, which drives a digest-pinned headless Chrome against the built dist/ and asserts on computed layout at widths derived from that CSS — one pixel either side of every breakpoint it declares, plus a 320px floor, a desktop baseline and two landscape sizes. See test/viewport/README.md for what it covers and what it genuinely cannot.

Rationale

When debugging network issues, it's useful to have a persistent at-a-glance view of latency and reachability to multiple well-known internet endpoints. NetWatch provides this as a zero-dependency SPA that can be deployed anywhere static files are served, with no backend required.

Design

The application is a single-page app built with Vite and Tailwind CSS v4. All code lives in src/main.js with a class-based architecture:

CONFIG: Frozen configuration object (update interval, timeouts, axis ticks, etc.)
HostState: Per-host state management — history buffer, latency tracking, status transitions
AppState: Top-level state container — WAN hosts, local hosts, pause state, aggregate stats
SparklineRenderer: Canvas 2D sparkline drawing with fixed axes, color-coded line segments, error regions, and DPR-aware scaling
UI functions: buildUI() constructs the DOM, updateHostRow() / updateSummary() / updateHealthBox() handle incremental updates
tick(): Main loop — measures all hosts in parallel via Promise.all, pushes samples, redraws UI. When paused, pushes blank markers (no probes, no false outage)

Monitoring targets

22 WAN hosts: datavi.be, Anthropic API, OpenAI API, AWS Console, GCP Console, Azure, Cloudflare, Fastly, Akamai, GitHub, B2, 7 S3 regional endpoints (Cape Town, London, Bahrain, Tokyo, Sydney, Oregon, São Paulo), 4 GCS locational endpoints (Iowa, Belgium, Singapore, Sydney)
Local CPE: Cable modem at 192.168.100.1 (always monitored)
Local Gateway: Auto-detected on startup by probing common default gateway addresses (192.168.1.1, 192.168.0.1, 192.168.8.1, 10.0.0.1); first responder wins. Note: modern browsers enforce Private Network Access restrictions that block public-origin pages from reaching RFC1918 addresses, so local targets only work when NetWatch is served from localhost or a private address.

Local hosts are tracked separately from WAN stats.

Latency measurement

HEAD requests with mode: 'no-cors' and cache: 'no-store', timed with performance.now(). 1-second timeout; anything over 1000ms is clamped to unreachable. IPv4 only.

Color coding

Latency	Color
< 50ms	Green
< 100ms	Lime
< 200ms	Yellow
< 500ms	Orange
>= 500ms	Red
Unreachable	Gray

Output structure

dist/
├── index.html
└── assets/
    ├── index-*.css
    └── index-*.js

Features

Real-time monitoring with 2s update interval and 300s history sparklines
Health indicator: green (HEALTHY) or red (DEGRADED) based on WAN reachability
Summary stats: reachable count, min/max/avg latency across WAN hosts only
Fixed chart axes: Y-axis 0–1000ms, X-axis 0–300s
Color-coded latency figures and sparkline line segments
Play/pause: pause stops probes but history keeps scrolling (blank gaps, no false outage)
Clickable service URLs
Canvas-based sparkline rendering with devicePixelRatio scaling
Zero runtime dependencies: all resources bundled into build artifacts

Deployment

After running yarn build, deploy the contents of the dist/ directory to any static file host (S3, GCS, Cloudflare Pages, Vercel, Netlify, GitHub Pages) or use the Docker image behind a reverse proxy.

The Docker image:

Listens on port 8080 by default (override with PORT env var)
Trusts X-Forwarded-For from RFC1918 reverse proxies (10/8, 172.16/12, 192.168/16)
Sends access logs to stdout
Caches static assets with immutable headers

Browser Compatibility

Requires a modern browser with ES modules, Fetch API, Canvas API, and CSS custom properties.

Limitations

CORS: Some hosts may block cross-origin HEAD requests. The app uses no-cors mode which allows the request but provides opaque responses. Latency is still measurable based on request timing.
Local gateway: The 192.168.100.1 endpoint requires the host to be accessible from your network.
Network conditions: Measurements reflect browser-to-endpoint latency, which includes your local network, ISP, and internet routing.

TODO

Add unit tests
Add eslint for JS linting (currently lint target runs prettier only)
Add configurable host list (environment variable or config file)
Add latency history export (CSV/JSON)
Add notification/alert when status changes to DEGRADED

License

MIT. See LICENSE.

Author

@sneak

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