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Async (HTTP)

Sooner or later your app must talk to a server, and the moment it does you inherit a family of problems: errors, timeouts, retries, loading states, stale replies racing each other.

re-frame2's answer is the managed request. You describe the request as data, return it from a pure event handler, and finish. The runtime performs it. The reply arrives later as an ordinary event — success and failure each named:

{:fx [[:rf.http/managed {:request    {:url "/api/articles/intro"}
                         :on-success [:article/loaded]
                         :on-failure [:article/load-error]}]]}

No await, no callback nesting, no resumed stack frame. The answer comes back on the same wire as everything else in your app.

In this section

  • Tutorial: talk to a server — build up from the smallest request that works to schema validation, retries, a cured search-box race, and a network-free test. Start here.
  • Managed HTTP reference — every key of :rf.http/managed: the request envelope, the reply contract, the closed set of failure categories, retry, cancellation, testing.
  • Interceptors and secrets — production cross-cutting concerns: stamp auth on every request once; keep tokens and passwords out of traces.
  • Your own async effect — wrap a promise-returning SDK, a callback API, or a worker message in the same pattern.
  • Why no await — the idea underneath it all: a continuation is data, not a closure. Read it once and every async surface in re-frame2 looks the same.
  • Examples — complete apps built on managed HTTP.

Scope

Two boundaries worth knowing before you dive in:

  • This section covers managed async — effects whose completion returns as a reply event. That's narrower than "async" in general: the event loop, dispatch-later, and the event pipeline are async too, and they live in Effects and Run to completion.
  • For the cache over server reads — staleness, invalidation, scope — see Resources, which rides on managed HTTP underneath. This section is the transport.

Setup

Managed HTTP ships as its own artefact, day8/re-frame2-http, so apps that never issue a request build clean of it. Add the dep and require re-frame.http.managed once at boot — that registers :rf.http/managed and family. The tutorial walks it.