From 9cd75c7c0d1432e061a94d2dce36a2006abfb346 Mon Sep 17 00:00:00 2001
From: Anna Henningsen <anna@addaleax.net>
Date: Tue, 23 Apr 2019 21:08:14 +0200
Subject: [PATCH] child_process: only stop readable side of stream passed to
 proc

Closing the underlying resource completely has the unwanted side effect
that the stream can no longer be used at all, including passing it
to other child processes.

What we want to avoid is accidentally reading from the stream;
accordingly, it should be sufficient to stop its readable side
manually, and otherwise leave the underlying resource intact.

Fixes: https://github.com/nodejs/node/issues/27097
Refs: https://github.com/nodejs/node/pull/21209
---
 lib/internal/child_process.js                 | 10 +++----
 .../test-child-process-server-close.js        |  6 ++--
 ...ld-process-stdio-merge-stdouts-into-cat.js | 30 +++++++++++++++++++
 3 files changed, 38 insertions(+), 8 deletions(-)
 create mode 100644 test/parallel/test-child-process-stdio-merge-stdouts-into-cat.js

diff --git a/lib/internal/child_process.js b/lib/internal/child_process.js
index 8e6a303a2e27a5..591ff8440537c0 100644
--- a/lib/internal/child_process.js
+++ b/lib/internal/child_process.js
@@ -384,12 +384,12 @@ ChildProcess.prototype.spawn = function(options) {
       continue;
     }
 
-    // The stream is already cloned and piped, thus close it.
+    // The stream is already cloned and piped, thus stop its readable side,
+    // otherwise we might attempt to read from the stream when at the same time
+    // the child process does.
     if (stream.type === 'wrap') {
-      stream.handle.close();
-      if (stream._stdio && stream._stdio instanceof EventEmitter) {
-        stream._stdio.emit('close');
-      }
+      stream.handle.readStop();
+      stream._stdio.pause();
       continue;
     }
 
diff --git a/test/parallel/test-child-process-server-close.js b/test/parallel/test-child-process-server-close.js
index ec95fed67b4fa7..d70926f2e8278e 100644
--- a/test/parallel/test-child-process-server-close.js
+++ b/test/parallel/test-child-process-server-close.js
@@ -8,11 +8,11 @@ const tmpdir = require('../common/tmpdir');
 tmpdir.refresh();
 
 const server = net.createServer((conn) => {
-  conn.on('close', common.mustCall());
-
   spawn(process.execPath, ['-v'], {
     stdio: ['ignore', conn, 'ignore']
-  }).on('close', common.mustCall());
+  }).on('close', common.mustCall(() => {
+    conn.end();
+  }));
 }).listen(common.PIPE, () => {
   const client = net.connect(common.PIPE, common.mustCall());
   client.on('data', () => {
diff --git a/test/parallel/test-child-process-stdio-merge-stdouts-into-cat.js b/test/parallel/test-child-process-stdio-merge-stdouts-into-cat.js
new file mode 100644
index 00000000000000..0158cbc2271aec
--- /dev/null
+++ b/test/parallel/test-child-process-stdio-merge-stdouts-into-cat.js
@@ -0,0 +1,30 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+
+// Regression test for https://github.com/nodejs/node/issues/27097.
+// Check that (cat [p1] ; cat [p2]) | cat [p3] works.
+
+const { spawn } = require('child_process');
+const p3 = spawn('cat', { stdio: ['pipe', 'pipe', process.stderr] });
+const p1 = spawn('cat', { stdio: ['pipe', p3.stdin, process.stderr] });
+const p2 = spawn('cat', { stdio: ['pipe', p3.stdin, process.stderr] });
+p3.stdout.setEncoding('utf8');
+
+// Write three different chunks:
+// - 'hello' from this process to p1 to p3 back to us
+// - 'world' from this process to p2 to p3 back to us
+// - 'foobar' from this process  to p3 back to us
+// Do so sequentially in order to avoid race conditions.
+p1.stdin.end('hello\n');
+p3.stdout.once('data', common.mustCall((chunk) => {
+  assert.strictEqual(chunk, 'hello\n');
+  p2.stdin.end('world\n');
+  p3.stdout.once('data', common.mustCall((chunk) => {
+    assert.strictEqual(chunk, 'world\n');
+    p3.stdin.end('foobar\n');
+    p3.stdout.once('data', common.mustCall((chunk) => {
+      assert.strictEqual(chunk, 'foobar\n');
+    }));
+  }));
+}));