Turbo streams patterns

Targeted Turbo Streams

Surgical DOM updates: broadcast/render specific <turbo-stream> actions against specific ids. Use this when you need precision (append a chat message, replace one card, move a class); use turbo-morphing when a whole-page refresh-with-morph is simpler. Full patterns: references/turbo-streams-guide.md.

When to use

• Live updates: model change → broadcast a partial to subscribers.
• A custom stream action Turbo doesn't ship (e.g. switch_class).
• A record's broadcasts are private — only authorized users may subscribe.
• Debugging: a stream that does nothing, a custom action the client ignores, or broadcasts arriving for the wrong user.

Patterns (and their footguns)

1. Model broadcast: after_create -> { broadcast_append_later_to parent, target:, partial: }. The _later variants enqueue a job — need an Active Job backend. View subscribes with turbo_stream_from parent, channel: "FooChannel".

2. Authorize the stream (security): turbo_stream_from only signs the stream name — it does NOT prove this user may receive that record's broadcasts. Use a custom channel that authorizes and rejects otherwise (templates/authorized_channel.rb.tmpl). The default Turbo::StreamsChannel streams from any signed name with no per-record check → eavesdropping risk.

3. Custom stream action = two halves that MUST match: a JS StreamActions.X and a Ruby helper registered via Turbo::Streams::TagBuilder.prepend (templates/custom_stream_action*.tmpl). One side alone fails silently.

4. Stream tags inside a frame response: to patch an element outside the frame you're rendering into, embed turbo_stream.* tags in the frame's HTML — no separate *.turbo_stream.erb needed.

5. Kredis presence: a kredis_set of online users (maintained in the channel's subscribed/unsubscribed) decides live-append vs also notifying/emailing.

Lint an app

scripts/lint_turbo_streams.sh path/to/rails-app

Flags: custom stream actions wired on only one side; channels that stream_from without authorizing the subscriber (broadcast eavesdropping — reported as an error); broadcast_*_later without a job backend; and (response-stream path) a *.turbo_stream.erb template whose literal slash-pathed partial: resolves to no file (→ MissingTemplate when that stream renders) or a custom turbo_stream.<action> with no client-side StreamActions.<action>. Heuristic grep scan (names its ceiling — bare/dynamic partials and target-id existence aren't resolved). Verified: clean on the Piazza app and on a real response-template app (miela_app, 14 templates), flags a synthetic leaky-channel + half-wired + dangling-partial app.