3 · gallery — files, events, and operations

examples/gallery/app.go is the async showcase: an image pipeline that is entirely event-driven.

var photos     = tako.Bucket("photos")
var photoStore = tako.Entity[Photo]("photos")
var thumbs     = tako.Queue[ThumbJob]("thumbnails")
var ready      = tako.Topic[PhotoReady]("photo-ready")

var OnUploaded  = tako.Subscribe(photos.Uploaded, onUploaded)
var MakeThumb   = tako.Worker(thumbs, makeThumb, tako.Compute{Profile: tako.ProfileBatch})
var NotifyOwner = tako.Subscribe(ready, notifyOwner)
var WarmFeed    = tako.Subscribe(ready, warmFeed)
var Cleanup     = tako.Cron("every 24h", cleanupOrphans, tako.CronConfig{Singleflight: true})

The pipeline

upload → bucket event → queue → worker (real image resize) → topic → two subscribers. Nobody calls anybody: events are the preferred inter-service style, and each hop is a compile-checked payload. Topic fan-out gives every subscriber its own delivery, retries, and dead letter — one failing never delays another.

Direct uploads (signed URLs)

photos.SignedPut(ctx, key, 15*time.Minute, tako.PutPolicy{ContentType: "image/*", ...}) returns a URL the browser PUTs to directly — no 32MB request cap, no proxying. The signed upload fires the same photos.Uploaded event, so the pipeline doesn't know or care how bytes arrived. Signed GETs shape downloads the same way.

Operations primitives

tako.Cache[T] with TTL (per-instance, honestly documented), GetOrFill for cold starts, warmed by the WarmFeed subscriber.
tako.Secret("notifier-key") resolves ONCE at startup — a missing secret refuses boot; Value() can never fail at request time.
tako.Counter / tako.Histogram for metrics.
tako.Compute{Profile: tako.ProfileBatch} on the thumb worker: its service gets batch scaling knobs (2 cpu, 2Gi, low concurrency).

Coordination

CronConfig.Singleflight on the cron collapses overlapping runs across all instances via a lease; tako.Lock("reindex") guards gallery's cross-entity repair the same way:

ran, err := relock.TryDo(ctx, rebuildFeed)  // false: already running somewhere

Locks are for critical SECTIONS (rebuilds, external systems) — single-entity atomicity is Tx's job. Crashes need no cleanup: the lease TTL expires and the next campaigner takes over.

Run it

cd examples/gallery
echo 'notifier-key=nk_dev_123' > .env
tako dev
# upload an image via multipart or the signed-URL flow; watch the
# pipeline narrate: event → queue → ⚙ worker → fan-out
tako test    # incl. chaos on the thumbnail path

Deployed, this graph becomes five services (the partition rule: sync handlers together, each async handler its own), four dead-letter topics, GCS notifications, and a page of derived grants — every line of which the security summary traces back to a code edge.