The reader app — go-reddit/reader

A native macOS Reddit reader whose entire UI is drawn by go-widgets — compiled to WebAssembly, blitted into a <canvas>, and hosted in a WKWebView that is opened from Go with zero cgo (CGO_ENABLED=0). Module path github.com/go-reddit/reader.

Architecture

┌─ "Reddit Reader.app"  (pure Go, CGO=0, self-contained) ───────────────┐
│                                                                        │
│   internal/ui        go-widgets toolkit renders the feed → RGBA buffer │
│   cmd/front  (wasm)  blits that buffer into a browser <canvas>         │
│   internal/server    serves the wasm + proxies /api → Reddit           │
│   internal/webview   opens a WKWebView via purego (no cgo)             │
│                                                                        │
│   Transport (default): a WKURLSchemeHandler serves every request       │
│   in-process — no TCP, no unix socket, no listening port at all.       │
│                                                                        │
│        fetch  reader://app/api/feed ──► go-reddit/reddit ──► reddit.com │
└────────────────────────────────────────────────────────────────────────┘

The layout mirrors the Reddit web UI: a topbar with sort tabs (hot/new/top/rising) and the current feed, a sidebar of bookmarked subreddits, and the scrollable feed of post cards.

Three choices worth calling out:

1. go-widgets, not HTML. The cards, score badges, sidebar and topbar are painted by the go-widgets painter into an RGBA buffer, exactly as in a native window — the WebView is just a surface. Text is anti-aliased TrueType rendered at device resolution, so it stays crisp at any zoom or on a Retina display.
2. CGO=0 everywhere. The WKWebView, NSWindow and NSApplication are driven through the Objective-C runtime via purego. The shipped binary links only system libraries; AppKit/WebKit are dlopened at runtime.
3. No socket. Instead of a loopback HTTP server, the default transport registers a private reader:// URL scheme and answers every request in-process from the same http.Handler. Nothing on the machine can reach the app's content, and no port is consumed. Pass -http to fall back to a 127.0.0.1 server (used off macOS and for automated testing).

Running it

task run                       # == go run .   (front page)
go run . -sr golang -sort top  # start on a specific feed
task app                       # build dist/Reddit Reader.app
task demo                      # built-in sample feeds, no network

For live Reddit from a datacenter IP, set OAuth credentials — see Authentication.

Flags & environment

Flag	Env	Meaning
-sr	READER_SUBREDDIT	subreddit (empty = front page)
-sort	READER_SORT	hot/new/top/rising/controversial/best
-demo		serve a built-in sample feed, no network
-http		use a loopback TCP server instead of the URL-scheme transport
-no-window		open the default browser instead of a native window
-serve-only		run headless over TCP and print the URL
	READER_OAUTH_CLIENT_ID / _SECRET	app-only OAuth
	READER_OAUTH_USERNAME / _PASSWORD	script-grant OAuth

Build layout

• internal/ui — the go-widgets scene: layout, hit-testing, rendering. Pure, native-testable (100% coverage), no build tag.
• cmd/front — the GOOS=js GOARCH=wasm entry point (syscall/js glue).
• internal/server — static bundle + /api proxy (100% coverage).
• internal/webview — the purego WKWebView + WKURLSchemeHandler bridge.

The wasm bundle is a build artifact; scripts/build-wasm.sh (run by every task target) produces internal/server/assets/reader.wasm.