AshHooks

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Hex.pm

Webhooks for Ash Framework, in both directions:

  • Inbound — receive provider webhooks, verify their signatures, deduplicate them on a database-unique ledger, and run your handler once per delivery.
  • Outbound — sign and deliver your own webhooks with retries, backoff, and dead-lettering, on any queue backed by Oban.

The two halves work independently: if you only receive webhooks, you need no queue infrastructure at all.

  • Verify signatures for ComplyCube and HubSpot v3 out of the box; bring your own scheme with a one-module provider behaviour.
  • Duplicate and replayed deliveries process exactly once on the ledger; crashes mid-flight resume on redelivery instead of losing events.
  • Outbound webhooks follow the Standard Webhooks spec, so receivers verify with any conformant library. Key rotation and a legacy-envelope mode for receivers mid-migration are built in.
  • Retries honor Retry-After, back off with jitter, dead-letter at a ceiling, and durably disable endpoints that return 410.
  • Safe defaults: secrets are only ever resolved through your callbacks (literal secrets are rejected at compile time), endpoint URLs are SSRF-checked at registration and again at send time, and response bodies are never stored unless you explicitly opt in for a diagnostic run.
  • Telemetry events for the whole send/receive lifecycle — structured so they can never leak secrets or payloads into your metrics backend.

Requires Elixir ~> 1.15 and Ash ~> 3.0. Oban (~> 2.20) is needed only for outbound delivery; Phoenix or Plug only for receiving.

Installation

def deps do
  [
    {:ash_hooks, "~> 0.1.0"},
    # only for outbound delivery:
    {:oban, "~> 2.20"}
  ]
end

Or mix igniter.install ash_hooks, which also tries to patch your endpoint's Plug.Parsers with a raw-body reader. Signature schemes sign the exact wire bytes, and a router plug cannot recover what the parser already consumed — so if the automatic patch didn't apply, add it yourself:

plug Plug.Parsers,
  parsers: [:json],
  pass: ["*/*"],
  body_reader: {AshHooks.BodyReader, :read_body, []},
  json_decoder: Phoenix.json_library()

By default every parsed request carries a cached copy of its raw body; pass [only: ["/webhooks"]] as the reader's third element to limit that memory cost to your webhook routes.

You also create your own tables — ash_hooks injects fields and identities onto your resources, and your migrations carry them, including the unique indexes the deduplication guarantee rests on. Complete, runnable migrations, resources, and setup are in the get-started tutorial.

Receiving webhooks

Declare an inbound source on a ledger resource:

use Ash.Resource,
  data_layer: AshPostgres.DataLayer,
  extensions: [AshHooks, AshHooks.InboundDelivery]

inbound_delivery do
  # provider event ids aren't unique across accounts — your scope slots
  # extend the dedup identity (each must be a non-nullable attribute)
  scope_identity([:account_id])
end

attributes do
  attribute(:account_id, :string, allow_nil?: false)
end

webhooks do
  inbound :comply_cube do
    secret {:app_env, [:my_app, :complycube_secret]}
  end
end

Secrets are always sources — an {m, f, a} callback, an {:app_env, path}, or a zero-arity function — never literal values.

From your controller, one call runs the whole pipeline: verify the signature over the raw bytes, persist the payload, deduplicate, claim under a lease, run the provider handler, and record the outcome.

case AshHooks.Ingress.ingest(Ledger, :comply_cube, conn.private[:ash_hooks_raw_body], %{
       signature: List.first(get_req_header(conn, "complycube-signature")),
       headers: Map.new(conn.req_headers),
       scope: %{"account_id" => conn.params["account_id"]}
     }) do
  {:ok, :created, %{status: :processed}} -> send_resp(conn, 200, "")
  {:ok, :created, _} -> send_resp(conn, 500, "")   # handler failed
  {:ok, :duplicate, _} -> send_resp(conn, 200, "") # already seen
  {:error, _} -> send_resp(conn, 400, "")          # bad signature/payload
end

Delivery semantics. A delivery that finished (:processed or :failed_permanent) is never processed again. A crash after your handler ran but before the ledger recorded it will re-run the handler on redelivery — so write handlers idempotent, keyed on the provider's event id. In short: durable deduplication, at-least-once handler invocation.

HubSpot's v3 scheme also signs the HTTP method and the full request URI, so its controller passes both — build the public URI from a base URL you configure, not from conn, which behind a TLS proxy carries the internal host and port.

claim_delivery/2, mark_processed/3, and friends are public if you want to drive the lease machine from your own async pipeline; AshHooks.Ingress.reap/1 re-drives deliveries whose claims died with an expired lease.

Sending webhooks

Declare the event on the emitting resource, point it at your subscription and delivery resources, and define one worker module:

defmodule MyApp.WebhookDeliveryWorker do
  use AshHooks.Worker,
    deliveries: MyApp.OutboundDelivery,
    endpoints: MyApp.WebhookEndpoint,
    secret_resolver: {MyApp.Secrets, :webhook_secret},
    queue: :webhooks
end

The secret resolver maps an endpoint's secret reference to its value — generate values with AshHooks.Signing.generate_secret/0, store them whole in your secret store, and return them unchanged.

Dispatch, wiring the worker's generated enqueue function:

{:ok, event} = AshHooks.Event.new(type: :order_paid, payload: Jason.encode!(order))

AshHooks.dispatch(Order, :order_paid, event,
  enqueue: {MyApp.WebhookDeliveryWorker, :enqueue}
)

Every matching enabled endpoint gets a durable delivery row carrying the exact bytes to sign. The worker signs per Standard Webhooks (the same webhook-id on every retry), succeeds only on 2xx, never follows redirects, honors Retry-After (bounded), backs off with jitter on 5xx and transport errors, dead-letters other client errors, and durably disables the endpoint on 410. An endpoint's failure never blocks delivery to its siblings.

The default HTTP adapter is a small native client with every read capped, so a hostile response can't balloon worker memory; OTP's :httpc is available as an alternative, and you can inject your own adapter for tests or proxies.

Response bodies are never stored — each delivery row keeps the status and a content-type summary. When debugging a misbehaving endpoint you can re-drive one row with body capture enabled, and the captured body is stored only after passing the package's redaction floor (homoglyph folding, decode-chain analysis, entropy checks — encoded secrets don't survive it). You can also plug in your own redaction callback for domain-specific tokens; see AshHooks.Delivery docs.

Signing modes. :standard (default) needs only the endpoint's secret_ref. :dual and :legacy additionally require a legacy_secret_ref — :dual emits both envelopes so receivers can migrate, :legacy emits only the old one.

Observability

Attach one handler to see the whole lifecycle — inbound verify/dedup/claim, enqueue failures, delivery attempt/result/backoff/dead-letter/endpoint-disable. Events carry ids, integers, fixed atoms, and classified reasons — never secrets, bodies, or payloads. The exact event list and a copy-paste attach_many block are in the AshHooks.Telemetry docs and the get-started tutorial.

Retention

Ledger and delivery rows accumulate by default (they ARE the dedup and audit record). When you want them bounded, drive the retention hooks on a schedule of your choosing (an Oban cron job, a mix task, a nightly job):

  • AshHooks.Ingress.prune/2 and AshHooks.Delivery.prune/2 delete TERMINAL rows older than a cutoff — retryable and in-flight rows are never touched. They key off the resource's inserted_at, so add Ash's timestamps() to the resource and its migration.
  • AshHooks.Ingress.redact_payload/4 rewrites a claimed row's payload under the claim fence (scrub sensitive fields while keeping the dedup identity; the original-bytes digest is preserved for audit).

Deleting a terminal row re-opens its dedup identity — a replayed webhook re-processes, a re-emitted outbound event re-sends — so set the TTL beyond any replay or re-emission horizon.

Further reading

License

MIT.