Project516 · Nov 1, 2026 · Nov 1, 2026
diff --git a/src/node.ts b/src/node.ts
@@ -14,6 +14,7 @@ import { JVM, LM_CLASS, LM_JAR } from "./jvm.ts";
 import { hostNatives } from "./hostnatives.ts";
 import { ImageBackend } from "./image.ts";
 import { NodeNet } from "./net-node.ts";
+import { PendingThrow } from "./thread.ts";
 import type { NetBackend } from "./sockets.ts";
 
 // A host directory exposed read-only (or writable) inside the VFS.
@@ -194,6 +195,20 @@ function exposeGc() {
   if (gc) g.gc = gc;
 }
 
+// Once the reader goes away (a closed pipe), writes fail with an IOException as
+// on HotSpot; without a listener, node exits on the stream's error event.
+const broken = new Set<NodeJS.WriteStream>();
+function hostOut(s: NodeJS.WriteStream) {
+  if (!s.listeners("error").includes(onOutError)) s.on("error", onOutError);
+  return (b: Uint8Array) => {
+    if (broken.has(s)) throw new PendingThrow("java/io/IOException", "Broken pipe");
+    s.write(b);
+  };
+}
+function onOutError(this: NodeJS.WriteStream) {
+  broken.add(this);
+}
+
 function nodeVm(o: NodeRunOptions): JVM {
   exposeGc();
   const vfs = new VFS();
@@ -232,8 +247,8 @@ function nodeVm(o: NodeRunOptions): JVM {
       const mod = await import(pathToFileURL(p).href);
       Object.assign(natives, nativeTable(mod));
     },
-    stdout: o.stdout ?? ((b) => process.stdout.write(b)),
-    stderr: o.stderr ?? ((b) => process.stderr.write(b)),
+    stdout: o.stdout ?? hostOut(process.stdout),
+    stderr: o.stderr ?? hostOut(process.stderr),
     stdin: o.input ? fixedInput(o.input) : () => new Promise((resolve) => {
       const onData = (d: Buffer) => { cleanup(); resolve(new Uint8Array(d)); };
       const onEnd = () => { cleanup(); resolve(null); };

diff --git a/test/pipe/Pipe.java b/test/pipe/Pipe.java
@@ -0,0 +1,20 @@
+import java.io.FileDescriptor;
+import java.io.FileOutputStream;
+import java.io.IOException;
+
+// Writes to stdout after its reader has gone, as under `| head -1`.
+public class Pipe {
+  public static void main(String[] args) throws Exception {
+    for (int i = 0; i < 20000; i++) System.out.println("line " + i);
+    // java-web learns of the closed pipe on node's next event loop turn
+    Thread.sleep(200);
+    System.out.println("after");
+    System.err.println("checkError " + System.out.checkError());
+    try (var raw = new FileOutputStream(FileDescriptor.out)) {
+      raw.write('x');
+      System.err.println("raw write ok");
+    } catch (IOException e) {
+      System.err.println("raw " + e.getMessage());
+    }
+  }
+}
diff --git a/test/programs.test.ts b/test/programs.test.ts
@@ -1,7 +1,7 @@
 // Compiles each test/java/*.java and checks that java-web prints exactly
 // what HotSpot prints, with the same exit code.
 
-import { execFileSync, spawnSync } from "node:child_process";
+import { execFileSync, spawn, spawnSync } from "node:child_process";
 import { chmodSync, copyFileSync, mkdirSync, mkdtempSync, readdirSync, readFileSync, rmSync, writeFileSync } from "node:fs";
 import { tmpdir } from "node:os";
 import { join } from "node:path";
@@ -64,6 +64,20 @@ test("System.gc collects under the command", { skip: !files.includes("Refs.java"
   assert.deepEqual({ stdout: got.stdout, code: got.status }, { stdout: ref.stdout, code: ref.status });
 });
 
+test("stdout closed by its reader", async () => {
+  const classes = join(root, "build", "test-pipe");
+  execFileSync(hotspot("javac"), ["-d", classes, join(root, "test", "pipe", "Pipe.java")]);
+  // reads the first chunk, then closes the pipe
+  const run = (cmd: string, args: string[]) => new Promise<{ stderr: string; code: number | null }>((resolve) => {
+    const p = spawn(cmd, [...args, "-cp", classes, "Pipe"], { stdio: ["ignore", "pipe", "pipe"] });
+    let stderr = "";
+    p.stderr.on("data", (d) => (stderr += d));
+    p.stdout.once("data", () => p.stdout.destroy());
+    p.on("close", (code) => resolve({ stderr, code }));
+  });
+  assert.deepEqual(await run(process.execPath, [join(root, "src", "node.ts")]), await run(hotspot("java"), []));
+});
+
 function flags(file: string, tool: string): string[] {
   const m = new RegExp(`^// ${tool}: (.*)$`, "m").exec(readFileSync(join(src, file), "utf8"));
   return m ? m[1].split(" ") : [];