fix(web): harden WhatsApp creds persistence

src/web/session.test.ts

@@ -1,5 +1,6 @@
 import { EventEmitter } from "node:events";
 import fsSync from "node:fs";
+import path from "node:path";
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 import { resetLogger, setLoggerOverride } from "../logging.js";
 import {
@@ -43,6 +44,7 @@ describe("web session", () => {
     ).saveCreds;
     // trigger creds.update listener
     sock.ev.emit("creds.update", {});
+    await new Promise<void>((resolve) => setImmediate(resolve));
     expect(saveCreds).toHaveBeenCalled();
   });
 
@@ -107,4 +109,129 @@ describe("web session", () => {
     expect(formatError(err)).toContain("Request Time-out");
     expect(formatError(err)).toContain("QR refs attempts ended");
   });
+
+  it("does not clobber creds backup when creds.json is corrupted", async () => {
+    const credsSuffix = path.join(".clawdis", "credentials", "creds.json");
+
+    const copySpy = vi
+      .spyOn(fsSync, "copyFileSync")
+      .mockImplementation(() => {});
+    const existsSpy = vi.spyOn(fsSync, "existsSync").mockImplementation((p) => {
+      if (typeof p !== "string") return false;
+      return p.endsWith(credsSuffix);
+    });
+    const statSpy = vi.spyOn(fsSync, "statSync").mockImplementation((p) => {
+      if (typeof p === "string" && p.endsWith(credsSuffix)) {
+        return { isFile: () => true, size: 12 } as never;
+      }
+      throw new Error(`unexpected statSync path: ${String(p)}`);
+    });
+    const readSpy = vi.spyOn(fsSync, "readFileSync").mockImplementation((p) => {
+      if (typeof p === "string" && p.endsWith(credsSuffix)) {
+        return "{" as never;
+      }
+      throw new Error(`unexpected readFileSync path: ${String(p)}`);
+    });
+
+    await createWaSocket(false, false);
+    const sock = getLastSocket();
+    const saveCreds = (
+      await baileys.useMultiFileAuthState.mock.results[0].value
+    ).saveCreds;
+
+    sock.ev.emit("creds.update", {});
+    await new Promise<void>((resolve) => setImmediate(resolve));
+
+    expect(copySpy).not.toHaveBeenCalled();
+    expect(saveCreds).toHaveBeenCalled();
+
+    copySpy.mockRestore();
+    existsSpy.mockRestore();
+    statSpy.mockRestore();
+    readSpy.mockRestore();
+  });
+
+  it("serializes creds.update saves to avoid overlapping writes", async () => {
+    let inFlight = 0;
+    let maxInFlight = 0;
+    let release: (() => void) | null = null;
+    const gate = new Promise<void>((resolve) => {
+      release = resolve;
+    });
+
+    const saveCreds = vi.fn(async () => {
+      inFlight += 1;
+      maxInFlight = Math.max(maxInFlight, inFlight);
+      await gate;
+      inFlight -= 1;
+    });
+    baileys.useMultiFileAuthState.mockResolvedValueOnce({
+      state: { creds: {}, keys: {} },
+      saveCreds,
+    });
+
+    await createWaSocket(false, false);
+    const sock = getLastSocket();
+
+    sock.ev.emit("creds.update", {});
+    sock.ev.emit("creds.update", {});
+
+    await new Promise<void>((resolve) => setImmediate(resolve));
+    expect(inFlight).toBe(1);
+
+    release?.();
+
+    // let both queued saves complete
+    await new Promise<void>((resolve) => setImmediate(resolve));
+    await new Promise<void>((resolve) => setImmediate(resolve));
+
+    expect(saveCreds).toHaveBeenCalledTimes(2);
+    expect(maxInFlight).toBe(1);
+    expect(inFlight).toBe(0);
+  });
+
+  it("rotates creds backup when creds.json is valid JSON", async () => {
+    const credsSuffix = path.join(".clawdis", "credentials", "creds.json");
+    const backupSuffix = path.join(".clawdis", "credentials", "creds.json.bak");
+
+    const copySpy = vi
+      .spyOn(fsSync, "copyFileSync")
+      .mockImplementation(() => {});
+    const existsSpy = vi.spyOn(fsSync, "existsSync").mockImplementation((p) => {
+      if (typeof p !== "string") return false;
+      return p.endsWith(credsSuffix);
+    });
+    const statSpy = vi.spyOn(fsSync, "statSync").mockImplementation((p) => {
+      if (typeof p === "string" && p.endsWith(credsSuffix)) {
+        return { isFile: () => true, size: 12 } as never;
+      }
+      throw new Error(`unexpected statSync path: ${String(p)}`);
+    });
+    const readSpy = vi.spyOn(fsSync, "readFileSync").mockImplementation((p) => {
+      if (typeof p === "string" && p.endsWith(credsSuffix)) {
+        return "{}" as never;
+      }
+      throw new Error(`unexpected readFileSync path: ${String(p)}`);
+    });
+
+    await createWaSocket(false, false);
+    const sock = getLastSocket();
+    const saveCreds = (
+      await baileys.useMultiFileAuthState.mock.results[0].value
+    ).saveCreds;
+
+    sock.ev.emit("creds.update", {});
+    await new Promise<void>((resolve) => setImmediate(resolve));
+
+    expect(copySpy).toHaveBeenCalledTimes(1);
+    const args = copySpy.mock.calls[0] ?? [];
+    expect(String(args[0] ?? "")).toContain(credsSuffix);
+    expect(String(args[1] ?? "")).toContain(backupSuffix);
+    expect(saveCreds).toHaveBeenCalled();
+
+    copySpy.mockRestore();
+    existsSpy.mockRestore();
+    statSpy.mockRestore();
+    readSpy.mockRestore();
+  });
 });

src/web/session.ts

@@ -23,6 +23,18 @@ export const WA_WEB_AUTH_DIR = path.join(CONFIG_DIR, "credentials");
 const WA_CREDS_PATH = path.join(WA_WEB_AUTH_DIR, "creds.json");
 const WA_CREDS_BACKUP_PATH = path.join(WA_WEB_AUTH_DIR, "creds.json.bak");
 
+let credsSaveQueue: Promise<void> = Promise.resolve();
+function enqueueSaveCreds(
+  saveCreds: () => Promise<void> | void,
+  logger: ReturnType<typeof getChildLogger>,
+): void {
+  credsSaveQueue = credsSaveQueue
+    .then(() => safeSaveCreds(saveCreds, logger))
+    .catch((err) => {
+      logger.warn({ error: String(err) }, "WhatsApp creds save queue error");
+    });
+}
+
 function readCredsJsonRaw(filePath: string): string | null {
   try {
     if (!fsSync.existsSync(filePath)) return null;
@@ -66,8 +78,15 @@ async function safeSaveCreds(
 ): Promise<void> {
   try {
     // Best-effort backup so we can recover after abrupt restarts.
-    if (fsSync.existsSync(WA_CREDS_PATH)) {
-      fsSync.copyFileSync(WA_CREDS_PATH, WA_CREDS_BACKUP_PATH);
+    // Important: don't clobber a good backup with a corrupted/truncated creds.json.
+    const raw = readCredsJsonRaw(WA_CREDS_PATH);
+    if (raw) {
+      try {
+        JSON.parse(raw);
+        fsSync.copyFileSync(WA_CREDS_PATH, WA_CREDS_BACKUP_PATH);
+      } catch {
+        // keep existing backup
+      }
     }
   } catch {
     // ignore backup failures
@@ -113,7 +132,7 @@ export async function createWaSocket(
     markOnlineOnConnect: false,
   });
 
-  sock.ev.on("creds.update", () => safeSaveCreds(saveCreds, sessionLogger));
+  sock.ev.on("creds.update", () => enqueueSaveCreds(saveCreds, sessionLogger));
   sock.ev.on(
     "connection.update",
     (update: Partial<import("@whiskeysockets/baileys").ConnectionState>) => {