feat(storage): atomic setIfAbsent primitive (client)#119
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Adds a race-free "write only if the key is not already set" command to plugin
storage: storage.setIfAbsent(key, value, { ttlSeconds? }) plus the pipeline
set_if_absent command. Resolves to the stored item on a win, or { value: undefined }
when the key already existed (claim lost) — mirroring the get-miss convention.
This is the client half; the platform (envoy-web PluginStorageService) must learn
the set_if_absent action for it to resolve. See docs/proposals/atomic-set-if-absent.md.
Motivation: integrations that provision from two concurrent paths (e.g. an event
webhook + an app-extension render, possibly on different pods) need a real
mutual-exclusion primitive. Today's get-then-set is a TOCTOU race and set_unique
overwrites. setIfAbsent lets exactly one caller win, resolved server-side against
the existing unique index.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Platform companion PR: envoy/envoy-web#21455 (adds the |
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Summary
Adds a race-free "write only if the key is not already set" primitive to plugin storage — the client half of a cross-repo change (platform companion PR in
envoy-web).storage.setIfAbsent(key, value, { ttlSeconds? })+ pipelineset_if_absentcommand.{ value: undefined }when the key already existed (claim lost) — same convention asget-miss /setUnique-exhaustion, so no new result shape.set_if_absentaction.Why
Some integrations provision from two concurrent paths for the same entity — e.g. an event webhook and an app-extension render — that can run at the same instant and on different pods. Both do
get → (missing) → create, and the idempotency record is only written after the external calls, so both see "missing" and both create (duplicate external records). This is a check-then-act (TOCTOU) race that a better read can't fix and that in-process de-duplication can't cover across pods.setoverwrites (last-write-wins) andset_uniqueguarantees a unique value (not key ownership), so neither can elect a single winner.setIfAbsentcan: the winner is decided atomically at the write, server-side, against the existing unique index onplugin_storage_items.Motivating case:
pacs-integration-service#202(By The Bay / Habitap credential provisioning).What's here
EnvoyStorageCommand— newset_if_absentaction +EnvoySetIfAbsentStorageCommand.EnvoyPluginStoragePipeline.setIfAbsent(...)andEnvoyPluginStorage.setIfAbsent(...).EnvoyPluginStoragePipelineMock(single-threaded existence check; TTL not modelled).docs/proposals/atomic-set-if-absent.md.tsc --noEmit,eslint, andjest(76 passing, +4 new) are green.Depends on
Platform companion PR in
envoy-webadding theset_if_absentaction toPlatform::PluginStorageService. This SDK method is a no-op until that lands. The two can merge in either order.🤖 Generated with Claude Code