test: add stream leak test case

test/js/web/streams/streams-leak.test.ts

@@ -0,0 +1,58 @@
+import { beforeAll, afterAll, test, expect } from "bun:test";
+import type { Subprocess } from "bun";
+
+var cat: Subprocess<"pipe", "pipe", "inherit">;
+var r: ReadableStreamDefaultReader<Uint8Array>;
+
+const BYTES_TO_WRITE = 1_000_000;
+beforeAll(() => {
+  cat = Bun.spawn(["cat"], {
+    stdin: "pipe",
+    stdout: "pipe",
+  });
+  r = cat.stdout.getReader() as any;
+});
+
+afterAll(() => {
+  r = null!;
+  cat.stdin.end();
+  cat.kill();
+});
+
+async function readAndWrite(bytes = BYTES_TO_WRITE) {
+  const buf = new Uint8Array(bytes);
+  await cat.stdin.write(buf);
+
+  let i = 0;
+  for (let chunks = 0; chunks < bytes; chunks++) {
+    const { value } = await r.read();
+    i += value?.length ?? 0;
+    if (i >= buf.length) {
+      return;
+    }
+  }
+  throw new Error("infinite loop");
+}
+
+// https://github.com/oven-sh/bun/issues/12198
+test("PullIntoDescriptors do not leak buffers", async () => {
+  const rounds = 100;
+  const warmup = 10;
+
+  for (let i = 0; i < warmup; i++) {
+    await readAndWrite(10_000);
+  }
+  Bun.gc(true);
+  const { arrayBuffers: arrayBuffersBefore, heapUsed: heapUsedBefore } = process.memoryUsage();
+
+  for (let i = 0; i < rounds; i++) {
+    await readAndWrite();
+  }
+  Bun.gc(true);
+  const { arrayBuffers: arrayBuffersAfter, heapUsed: heapUsedAfter } = process.memoryUsage();
+
+  const newArrayBuffers = arrayBuffersAfter - arrayBuffersBefore;
+  const newHeapUsed = heapUsedAfter - heapUsedBefore;
+  expect(newArrayBuffers).toBeLessThan(rounds / 2);
+  expect(newHeapUsed).toBeLessThan((BYTES_TO_WRITE * rounds) / 2);
+});