BabelQueue · muhammetsafak · Jun 19, 2026 · Jun 19, 2026
diff --git a/package.json b/package.json
@@ -59,7 +59,7 @@
     "build": "tsup",
     "typecheck": "tsc --noEmit",
     "lint": "eslint src test",
-    "test": "node --import tsx --test test/codec.test.ts test/dead-letter.test.ts test/conformance.test.ts test/overhead.test.ts test/idempotency.test.ts test/schema.test.ts test/otel.test.ts",
+    "test": "node --import tsx --test test/codec.test.ts test/dead-letter.test.ts test/conformance.test.ts test/overhead.test.ts test/idempotency.test.ts test/schema.test.ts test/otel.test.ts test/redrive.test.ts",
     "coverage": "c8 --check-coverage --lines 90 --functions 90 --branches 85 --reporter=text npm test",
     "prepublishOnly": "npm run build"
   },

diff --git a/src/index.ts b/src/index.ts
@@ -38,3 +38,12 @@ export type { Handler, Store } from "./idempotency.js";
 
 export * as schema from "./schema.js";
 export type { SchemaProvider, SchemaNode } from "./schema.js";
+
+export { redrive, resetForRedrive } from "./redrive.js";
+export type {
+  RedriveIO,
+  RedriveItem,
+  RedriveMessage,
+  RedriveOptions,
+  RedriveResult,
+} from "./redrive.js";
diff --git a/src/redrive.ts b/src/redrive.ts
@@ -0,0 +1,170 @@
+/**
+ * DLQ redrive tooling — safe replay off the dead-letter queue (ADR-0026).
+ *
+ * The Node mirror of the Go reference `babelqueue-go/redrive.go`. Because the Node core is
+ * codec-only (no runtime / no transport), the orchestration takes a small {@link RedriveIO}
+ * the caller implements over their transport — the same shape the optional `otel.publish`
+ * helper used. {@link resetForRedrive} is the pure, transport-free core of it.
+ *
+ * A redriven message is **reset for reprocessing**: its `dead_letter` block is removed and
+ * `attempts` reset to 0, while `job`, `trace_id`, `data` and `meta` are preserved verbatim, so
+ * the replay is still fully traceable (same `trace_id`). The wire envelope is untouched (GR-1).
+ *
+ * Replay safety here is `dryRun` + `select` + redrive-to-`toQueue` (a sandbox). The
+ * **Replay-Bypass** guard — a `bq-replay-bypass` transport header surfaced to handlers so a
+ * replay can skip external side-effects — is a documented phase-two follow-up that touches the
+ * runtime + every transport, like ADR-0025's `traceparent` follow-up.
+ */
+
+import { EnvelopeCodec, type Envelope } from "./codec.js";
+
+/** A message reserved from a queue, plus a way to acknowledge (remove) it. */
+export interface RedriveMessage {
+  body: string;
+  ack(): Promise<void>;
+}
+
+/** The minimal transport surface {@link redrive} needs: reserve the next message, and publish. */
+export interface RedriveIO {
+  /** Reserve the next message from queue, or `null` when it is empty. */
+  pop(queue: string): Promise<RedriveMessage | null>;
+  /** Append an already-encoded body to queue. */
+  publish(queue: string, body: string): Promise<void>;
+}
+
+/** Options for {@link redrive}. */
+export interface RedriveOptions {
+  /** Override where messages are re-published; default is each message's `dead_letter.original_queue`. Set a sandbox queue to replay safely. */
+  toQueue?: string;
+  /** Cap how many messages are pulled from the DLQ (0 / omitted = all currently available). */
+  max?: number;
+  /** Inspect without redriving: every message is read, reported, and returned to the DLQ unchanged. */
+  dryRun?: boolean;
+  /** Pick which messages to redrive (e.g. by reason or URN). Unselected messages are returned unchanged. */
+  select?: (envelope: Envelope) => boolean;
+}
+
+/** What happened to one message during a {@link redrive} run. */
+export interface RedriveItem {
+  messageId: string;
+  traceId: string;
+  urn: string;
+  reason: string;
+  from: string;
+  /** Target queue (the plan, even on a dry run; "" when skipped or undecodable). */
+  to: string;
+  /** True only when actually re-published to `to`. */
+  redriven: boolean;
+}
+
+/** Summary of a {@link redrive} run. */
+export interface RedriveResult {
+  redriven: number;
+  skipped: number;
+  items: RedriveItem[];
+}
+
+/**
+ * Returns a copy of `envelope` reset for reprocessing: no `dead_letter` block and `attempts`
+ * at 0, with `job`, `trace_id`, `data` and `meta` preserved verbatim. Pure — the input is not
+ * mutated.
+ */
+export function resetForRedrive(envelope: Envelope): Envelope {
+  return {
+    job: envelope.job,
+    trace_id: envelope.trace_id,
+    data: envelope.data,
+    meta: envelope.meta,
+    attempts: 0,
+  };
+}
+
+function sourceQueueOf(envelope: Envelope): string {
+  return envelope.dead_letter?.original_queue || envelope.meta.queue;
+}
+
+/**
+ * Moves dead-lettered messages off the `dlq` queue and re-publishes each — via {@link resetForRedrive} —
+ * to its `dead_letter.original_queue` or `opts.toQueue`.
+ *
+ * Messages are drained from the DLQ first and then processed, so restored messages (skipped,
+ * dry-run, or undecodable) are never re-encountered in the same run. A message is acknowledged
+ * only after its re-publish succeeds; an undecodable body is restored, not dropped. On a publish
+ * failure the message is restored to the DLQ and the error is re-thrown.
+ */
+export async function redrive(
+  io: RedriveIO,
+  dlq: string,
+  opts: RedriveOptions = {},
+): Promise<RedriveResult> {
+  const max = opts.max ?? 0;
+
+  interface Pending {
+    message: RedriveMessage;
+    envelope: Envelope | null;
+  }
+  const batch: Pending[] = [];
+  while (max === 0 || batch.length < max) {
+    const message = await io.pop(dlq);
+    if (!message) {
+      break;
+    }
+    const decoded = EnvelopeCodec.decode(message.body);
+    batch.push({ message, envelope: EnvelopeCodec.accepts(decoded) ? decoded : null });
+  }
+
+  const result: RedriveResult = { redriven: 0, skipped: 0, items: [] };
+
+  for (const { message, envelope } of batch) {
+    if (!envelope) {
+      await io.publish(dlq, message.body); // restore the undecodable body; never drop it
+      await message.ack();
+      result.skipped++;
+      result.items.push({ messageId: "", traceId: "", urn: "", reason: "", from: dlq, to: "", redriven: false });
+      continue;
+    }
+
+    const item: RedriveItem = {
+      messageId: envelope.meta.id,
+      traceId: envelope.trace_id,
+      urn: EnvelopeCodec.urn(envelope),
+      reason: envelope.dead_letter?.reason ?? "",
+      from: dlq,
+      to: "",
+      redriven: false,
+    };
+
+    if (opts.select && !opts.select(envelope)) {
+      await io.publish(dlq, message.body); // not selected: restore unchanged
+      await message.ack();
+      result.skipped++;
+      result.items.push(item);
+      continue;
+    }
+
+    const target = opts.toQueue ?? sourceQueueOf(envelope);
+    item.to = target;
+
+    if (opts.dryRun) {
+      await io.publish(dlq, message.body); // report the plan; restore unchanged
+      await message.ack();
+      result.skipped++;
+      result.items.push(item);
+      continue;
+    }
+
+    try {
+      await io.publish(target, EnvelopeCodec.encode(resetForRedrive(envelope)));
+    } catch (err) {
+      await io.publish(dlq, message.body); // restore on a publish failure
+      await message.ack();
+      throw err;
+    }
+    await message.ack();
+    item.redriven = true;
+    result.redriven++;
+    result.items.push(item);
+  }
+
+  return result;
+}
diff --git a/test/redrive.test.ts b/test/redrive.test.ts
@@ -0,0 +1,159 @@
+import assert from "node:assert/strict";
+import { test } from "node:test";
+
+import { EnvelopeCodec, type Envelope } from "../src/codec.js";
+import {
+  redrive,
+  resetForRedrive,
+  type RedriveIO,
+  type RedriveMessage,
+} from "../src/redrive.js";
+
+// memoryIO is a tiny in-memory RedriveIO over a Map of queues, with a queue() accessor for assertions.
+function memoryIO(): RedriveIO & { queue(name: string): string[]; failOn?: string } {
+  const queues = new Map<string, string[]>();
+  const q = (name: string): string[] => {
+    let arr = queues.get(name);
+    if (!arr) {
+      arr = [];
+      queues.set(name, arr);
+    }
+    return arr;
+  };
+  const io: RedriveIO & { queue(name: string): string[]; failOn?: string } = {
+    queue: q,
+    async pop(queue: string): Promise<RedriveMessage | null> {
+      const arr = q(queue);
+      if (arr.length === 0) {
+        return null;
+      }
+      const body = arr.shift() as string;
+      return {
+        body,
+        async ack(): Promise<void> {},
+      };
+    },
+    async publish(queue: string, body: string): Promise<void> {
+      if (io.failOn && queue === io.failOn) {
+        throw new Error(`publish refused for ${queue}`);
+      }
+      q(queue).push(body);
+    },
+  };
+  return io;
+}
+
+function deadLetteredBody(urn: string, originalQueue: string, data: Record<string, unknown> = {}): string {
+  const base = EnvelopeCodec.make(urn, data, { queue: originalQueue });
+  const dl: Envelope = {
+    ...base,
+    attempts: 3,
+    dead_letter: {
+      reason: "failed",
+      error: "boom",
+      exception: "Error",
+      failed_at: 1,
+      original_queue: originalQueue,
+      attempts: 3,
+      lang: "node",
+    },
+  };
+  return EnvelopeCodec.encode(dl);
+}
+
+test("resetForRedrive strips dead_letter and resets attempts, without mutating the input", () => {
+  const base = EnvelopeCodec.make("urn:babel:orders:created", { order_id: 1 }, { queue: "orders" });
+  const input: Envelope = { ...base, attempts: 3, dead_letter: { reason: "failed", error: null, exception: null, failed_at: 1, original_queue: "orders", attempts: 3, lang: "node" } };
+
+  const out = resetForRedrive(input);
+  assert.equal(out.dead_letter, undefined);
+  assert.equal(out.attempts, 0);
+  assert.equal(out.trace_id, input.trace_id);
+  assert.equal(out.job, input.job);
+  // input untouched
+  assert.ok(input.dead_letter);
+  assert.equal(input.attempts, 3);
+});
+
+test("redrive sends a message back to its source queue, reset and traceable", async () => {
+  const io = memoryIO();
+  io.queue("orders.dlq").push(deadLetteredBody("urn:babel:orders:created", "orders", { order_id: 1 }));
+  const traceId = EnvelopeCodec.decode(io.queue("orders.dlq")[0]).trace_id;
+
+  const res = await redrive(io, "orders.dlq");
+  assert.deepEqual([res.redriven, res.skipped], [1, 0]);
+
+  assert.equal(io.queue("orders.dlq").length, 0, "DLQ should be drained");
+  assert.equal(io.queue("orders").length, 1);
+  const back = EnvelopeCodec.decode(io.queue("orders")[0]);
+  assert.equal(back.dead_letter, undefined);
+  assert.equal(back.attempts, 0);
+  assert.equal(back.trace_id, traceId);
+});
+
+test("redrive routes to a sandbox queue without touching the source", async () => {
+  const io = memoryIO();
+  io.queue("orders.dlq").push(deadLetteredBody("urn:babel:orders:created", "orders"));
+
+  const res = await redrive(io, "orders.dlq", { toQueue: "sandbox" });
+  assert.equal(res.redriven, 1);
+  assert.equal(io.queue("orders").length, 0);
+  assert.equal(io.queue("sandbox").length, 1);
+});
+
+test("dryRun reports the plan and leaves the DLQ unchanged", async () => {
+  const io = memoryIO();
+  io.queue("orders.dlq").push(deadLetteredBody("urn:babel:orders:created", "orders"));
+
+  const res = await redrive(io, "orders.dlq", { dryRun: true });
+  assert.deepEqual([res.redriven, res.skipped], [0, 1]);
+  assert.equal(res.items[0].to, "orders");
+  assert.equal(res.items[0].redriven, false);
+  assert.equal(io.queue("orders").length, 0, "source untouched");
+  assert.equal(io.queue("orders.dlq").length, 1, "DLQ unchanged");
+  assert.ok(EnvelopeCodec.decode(io.queue("orders.dlq")[0]).dead_letter, "dead_letter intact");
+});
+
+test("select redrives only the matching messages, restoring the rest", async () => {
+  const io = memoryIO();
+  io.queue("dlq").push(deadLetteredBody("urn:babel:orders:created", "orders"));
+  io.queue("dlq").push(deadLetteredBody("urn:babel:emails:welcome", "emails"));
+
+  const res = await redrive(io, "dlq", {
+    select: (e) => EnvelopeCodec.urn(e) === "urn:babel:orders:created",
+  });
+  assert.deepEqual([res.redriven, res.skipped], [1, 1]);
+  assert.equal(io.queue("orders").length, 1);
+  assert.equal(io.queue("emails").length, 0);
+  assert.equal(io.queue("dlq").length, 1, "unselected restored to the DLQ");
+});
+
+test("max caps how many messages are pulled", async () => {
+  const io = memoryIO();
+  for (let i = 0; i < 3; i++) {
+    io.queue("dlq").push(deadLetteredBody("urn:babel:orders:created", "orders"));
+  }
+  const res = await redrive(io, "dlq", { max: 2 });
+  assert.equal(res.redriven, 2);
+  assert.equal(io.queue("dlq").length, 1);
+});
+
+test("a publish failure restores the message to the DLQ and re-throws", async () => {
+  const io = memoryIO();
+  io.queue("dlq").push(deadLetteredBody("urn:babel:orders:created", "orders"));
+  io.failOn = "orders";
+
+  await assert.rejects(redrive(io, "dlq"), /publish refused/);
+  assert.equal(io.queue("dlq").length, 1, "message restored to the DLQ");
+  assert.equal(io.queue("orders").length, 0);
+});
+
+test("an undecodable body is restored, not lost", async () => {
+  const io = memoryIO();
+  io.queue("dlq").push("not-json{{{");
+
+  const res = await redrive(io, "dlq");
+  assert.deepEqual([res.redriven, res.skipped], [0, 1]);
+  assert.equal(io.queue("dlq").length, 1);
+  assert.equal(io.queue("dlq")[0], "not-json{{{");
+});