fix(qa): normalize malformed JSON errors (#102830)

Co-authored-by: ZengWen-DT <ceng.wen@xydigit.com>

extensions/qa-lab/src/bus-server.test.ts

@@ -172,6 +172,19 @@ describe("qa-bus server", () => {
     });
   });
 
+  it("returns a controlled error when a v1 POST body contains malformed JSON", async () => {
+    const state = createQaBusState();
+    const bus = await startQaBusServer({ state });
+    stops.push(bus["stop"]);
+
+    const response = await postQaBusRawJson(bus.baseUrl, "/v1/reset", "{");
+
+    expect(response.status).toBe(400);
+    await expect(response.json()).resolves.toEqual({
+      error: "Malformed JSON body",
+    });
+  });
+
   it("keeps oversized numeric poll and search fields bounded", async () => {
     const state = createQaBusState();
     const bus = await startQaBusServer({ state });

extensions/qa-lab/src/bus-server.ts

@@ -26,6 +26,18 @@ const QA_HTTP_JSON_BODY_TIMEOUT_MS = 5_000;
 const QA_BUS_POLL_TIMEOUT_MAX_MS = 30_000;
 const QA_BUS_POLL_LIMIT_MAX = 500;
 const QA_BUS_SEARCH_LIMIT_MAX = 100;
+const QA_MALFORMED_JSON_BODY_MESSAGE = "Malformed JSON body";
+
+class QaMalformedJsonBodyError extends Error {
+  constructor() {
+    super(QA_MALFORMED_JSON_BODY_MESSAGE);
+    this.name = "QaMalformedJsonBodyError";
+  }
+}
+
+export function isQaMalformedJsonBodyError(error: unknown): error is Error {
+  return error instanceof QaMalformedJsonBodyError;
+}
 
 export async function readQaJsonBody(req: IncomingMessage): Promise<unknown> {
   const text = (
@@ -34,7 +46,14 @@ export async function readQaJsonBody(req: IncomingMessage): Promise<unknown> {
       timeoutMs: QA_HTTP_JSON_BODY_TIMEOUT_MS,
     })
   ).trim();
-  return text ? (JSON.parse(text) as unknown) : {};
+  if (!text) {
+    return {};
+  }
+  try {
+    return JSON.parse(text) as unknown;
+  } catch {
+    throw new QaMalformedJsonBodyError();
+  }
 }
 
 export function writeJson(res: ServerResponse, statusCode: number, body: unknown) {

extensions/qa-lab/src/lab-server.test.ts

@@ -6,12 +6,12 @@ import path from "node:path";
 import { setTimeout as sleep } from "node:timers/promises";
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 import { readQaJsonBody } from "./bus-server.js";
+import { resolveUiAssetVersion } from "./lab-server-ui.js";
 import {
   startQaLabServer,
   writeQaLabServerError,
   type QaLabServerStartParams,
 } from "./lab-server.js";
-import { resolveUiAssetVersion } from "./lab-server-ui.js";
 
 const qaChannelMock = vi.hoisted(() => ({
   resolveAccount: vi.fn(),
@@ -639,6 +639,26 @@ describe("qa-lab server", () => {
     expect(JSON.parse(res.body)).toEqual({ error: "Payload too large" });
   });
 
+  it("returns controlled errors for malformed JSON body reads", async () => {
+    const lab = await startQaLabServerForTest();
+    cleanups.push(async () => {
+      await lab.stop();
+    });
+
+    const response = await fetch(`${lab.baseUrl}/api/inbound/message`, {
+      method: "POST",
+      headers: {
+        "content-type": "application/json",
+      },
+      body: "{",
+    });
+
+    expect(response.status).toBe(400);
+    await expect(response.json()).resolves.toEqual({
+      error: "Malformed JSON body",
+    });
+  });
+
   it("anchors direct self-check runs under the explicit repo root by default", async () => {
     const repoRoot = await mkdtemp(path.join(os.tmpdir(), "qa-lab-self-check-root-"));
     cleanups.push(async () => {

extensions/qa-lab/src/lab-server.ts

@@ -10,6 +10,7 @@ import {
 import {
   closeQaHttpServer,
   handleQaBusRequest,
+  isQaMalformedJsonBodyError,
   readQaJsonBody,
   writeError,
   writeJson,
@@ -76,6 +77,10 @@ export function writeQaLabServerError(res: Parameters<typeof writeError>[0], err
   if (writeQaRequestBodyLimitError(res, error)) {
     return;
   }
+  if (isQaMalformedJsonBodyError(error)) {
+    writeError(res, 400, error.message);
+    return;
+  }
   if (error instanceof QaEvidenceGalleryError) {
     writeError(res, error.statusCode, error.message);
     return;