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idempotency.sx: persist/append-once appends at most once per (stream, idempotency key), returning the same event on a repeat. The marker lives in the kv facet, so idempotency holds across a restart (verified on durable). persist/seen? check. 180/180. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
29 lines
1.1 KiB
Plaintext
29 lines
1.1 KiB
Plaintext
; persist/idempotency — exactly-once append under retries. A command retried
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; after a network blip must not append its event twice. The caller supplies an
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; idempotency key; the first append for that (stream, key) stores the event and
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; remembers the key in the kv facet; a repeat returns the SAME event without
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; appending. Because the marker lives in kv, idempotency holds across a restart
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; too. Keyed per stream. Requires: lib/persist/log.sx, lib/persist/kv.sx.
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(define persist/idem-key (fn (stream key) (str "idem/" stream "/" key)))
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; true if an append-once has already been recorded for (stream, key)
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(define
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persist/seen?
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(fn (b stream key) (persist/kv-has? b (persist/idem-key stream key))))
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; append at most once per (stream, key). Returns the stored event either way —
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; freshly appended on first use, the remembered one on a repeat.
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(define
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persist/append-once
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(fn
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(b stream key type at data)
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(let
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((k (persist/idem-key stream key)))
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(if
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(persist/kv-has? b k)
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(persist/kv-get b k)
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(let
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((ev (persist/append b stream type at data)))
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(begin (persist/kv-put b k ev) ev))))))
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