Early Data Replay and Safe Request Admission

Working case

Reviewer 47 opens a case detail page, then submits a permit approval while a resumed connection sends early data. A replayed approval could create two audit entries or notify two contractors. The gateway forwards safe case reads but rejects the approval attempt until a completed handshake, then the client retries under a stable operation identity. The origin also checks the current case version and reviewer permission. A one-use sign-in callback is excluded from early processing because replaying it can consume state in the wrong order. The page reports an approval only after one durable commit.

Implementation boundary

function mayUseEarlyData(requestKind) {
  return requestKind === "public-read" || requestKind === "authorized-pure-read";
}
console.log(mayUseEarlyData("case-approval"));
// Output: false

Identify whether the edge or reverse proxy can receive and forward early data; do not assume application code sees the transport detail automatically. Classify routes by effects, not just HTTP method labels. A read that rotates a token or creates a job is not replay-safe merely because it uses GET. Reject unsafe early requests with the supported retry signal, and ensure any intermediary understands and preserves that decision before forwarding. The retry must occur after the handshake, not as another early attempt. On the origin, use a stable idempotency key for retryable writes and conditional version checks for concurrent edits. These controls address different failure modes. Never place a private approval or payment side effect behind a cache or retry layer whose behavior is unknown.

Cost and boundaries

Blocking early mutation can add a handshake round trip to that action, which is usually cheaper than reconciling a duplicate side effect. Idempotency storage costs O(W) for W recent operations and needs a retention window longer than likely retries. Conditional writes add a database check or transaction condition. A route-level classification requires upkeep as endpoint behavior changes. Measure how often unsafe early requests are rejected, retry success, duplicate-effect attempts, and approval latency. Avoid turning early-data status into an unbounded log dimension with full private URLs.

Failure trace

Replay an approval request and confirm one committed case version, one audit entry, and one notification. Return a retry signal for an early request but have a proxy automatically resend it as early data again; detect the loop and fix gateway behavior. Mark a one-use callback GET as safe solely by method and show why it is not. Lose a committed approval response, then retry with the same operation key after the handshake and return the recorded result. Change reviewer permission before the retry and define whether the recorded result can be read by that actor without leaking protected data.

Verification

Route classification accounts for hidden effects, not method names alone.
Unsafe early requests wait for a completed handshake and retry safely.
A replayed mutation produces one durable effect.

Practice drill

Classify 63 portal routes into safe early reads, unsafe reads with effects, and mutations. Simulate a resumed connection for case 29, one approval replay, a one-use login callback, and a lost response after commit. Record the gateway decision, origin write count, audit count, returned status, and retry timing for each. Change the case version between original attempt and retry, then verify the idempotency record and conditional version check give a consistent outcome. Repeat through the backup proxy, not only the primary path.

Decision note

A faster handshake cannot justify replayable state change; admit early requests only when the whole route is safe under replay.

Common Mistakes

Assuming every GET is replay-safe.
Letting a gateway forward unsafe early data without origin awareness.
Using an idempotency key as a substitute for current permission and version checks.

Apply and check

Build Project: permit domain cutover and transport recovery and review Web Development: network transport operations quiz.