Deduplicate retries with a durable inbox · AI Engineering

Persist accepted identity and body before acknowledging delivery.

Type: Build Languages: Go Stage: 3 of 4 Prerequisites: Basic functions, collections, JSON and the previous stages when applicable. Time: ~2 hours

What you build

Write a mode-0600 temporary file, sync its content, and publish it through an atomic no-overwrite hard link. Sync the directory before acknowledging success. Delivery filenames are SHA-256 digests of IDs, preventing path traversal. Existing IDs with identical raw bytes are transport retries; changed bytes are conflicts.

Worked example

The first signed delivery returns HTTP 202. The same ID and bytes return 200 without replacing the original acceptedAt. The same ID with a newly valid signature but a different body returns 409. A changed body under the old signature returns 401 before storage.

pj signed webhook inbox 3

Implement the contract

Accept(dir,id,body,now)(Entry,created,error); LoadEntry(dir,id)(Entry,error). Entry stores schemaVersion, deliveryId, base64 body, sha256 and acceptedAt. ErrConflict identifies reused delivery IDs. Corrupt stored records fail closed.

Reject malformed input before producing a partial artifact. The tests include held-out records separate from the demonstration fixture.

Run your work

bash

python3 scripts/project_test.py signed-webhook-inbox --init /tmp/signed-webhook-inbox-work
python3 scripts/project_test.py signed-webhook-inbox --stage 3 --path /tmp/signed-webhook-inbox-work --strict

Initialization copies cumulative scaffolding without replacing your work. Implement the TODO functions in the first-stage starter; later-stage starter notes describe the new behavior. Tests import the learner workspace. Run the command in the README against your own input after passing the stage.

Inspect and extend

Kill a process between writing and linking. Unlinked .pending files can remain but are never accepted deliveries. This local-filesystem design requires hard-link and fsync support; do not claim equivalent behavior on arbitrary network filesystems.

Go standard library and Node standard library. All fixtures and implementations are original.