child_process: use non-infinite maxBuffer defaults

Set the default maxBuffer size to 204,800 bytes for execSync,
execFileSync, and spawnSync.

APIs that return the child output as a string should have non-infinite
defaults for maxBuffer sizes to avoid out-of-memory error conditions. A
non-infinite default used to be the documented behaviour for all
relevant APIs, but the implemented behaviour for execSync, execFileSync
and spawnSync was to have no maxBuffer limits.

PR-URL: #23027
Refs: #22894
Reviewed-By: Sam Roberts <vieuxtech@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

doc/api/child_process.md

@@ -721,7 +721,7 @@ changes:
     process will be killed. **Default:** `'SIGTERM'`.
   * `maxBuffer` {number} Largest amount of data in bytes allowed on stdout or
     stderr. If exceeded, the child process is terminated. See caveat at
-    [`maxBuffer` and Unicode][]. **Default:** `Infinity`.
+    [`maxBuffer` and Unicode][]. **Default:** `200 * 1024`.
   * `encoding` {string} The encoding used for all stdio inputs and outputs.
     **Default:** `'buffer'`.
   * `windowsHide` {boolean} Hide the subprocess console window that would
@@ -788,7 +788,7 @@ changes:
   * `maxBuffer` {number} Largest amount of data in bytes allowed on stdout or
     stderr. If exceeded, the child process is terminated and any output is
     truncated. See caveat at [`maxBuffer` and Unicode][].
-    **Default:** `Infinity`.
+    **Default:** `200 * 1024`.
   * `encoding` {string} The encoding used for all stdio inputs and outputs.
     **Default:** `'buffer'`.
   * `windowsHide` {boolean} Hide the subprocess console window that would
@@ -852,7 +852,7 @@ changes:
   * `maxBuffer` {number} Largest amount of data in bytes allowed on stdout or
     stderr. If exceeded, the child process is terminated and any output is
     truncated. See caveat at [`maxBuffer` and Unicode][].
-    **Default:** `Infinity`.
+    **Default:** `200 * 1024`.
   * `encoding` {string} The encoding used for all stdio inputs and outputs.
     **Default:** `'buffer'`.
   * `shell` {boolean|string} If `true`, runs `command` inside of a shell. Uses

lib/child_process.js

@@ -46,6 +46,8 @@ const {
   ChildProcess
 } = child_process;
 
+const MAX_BUFFER = 200 * 1024;
+
 exports.ChildProcess = ChildProcess;
 
 function stdioStringToArray(option) {
@@ -206,7 +208,7 @@ exports.execFile = function execFile(file /* , args, options, callback */) {
   options = {
     encoding: 'utf8',
     timeout: 0,
-    maxBuffer: 200 * 1024,
+    maxBuffer: MAX_BUFFER,
     killSignal: 'SIGTERM',
     cwd: null,
     env: null,
@@ -560,7 +562,11 @@ var spawn = exports.spawn = function spawn(file, args, options) {
 function spawnSync(file, args, options) {
   const opts = normalizeSpawnArguments(file, args, options);
 
-  options = opts.options;
+  const defaults = {
+    maxBuffer: MAX_BUFFER,
+    ...opts.options
+  };
+  options = opts.options = Object.assign(defaults, opts.options);
 
   debug('spawnSync', opts.args, options);
 

test/parallel/test-async-wrap-pop-id-during-load.js

@@ -16,7 +16,8 @@ const { spawnSync } = require('child_process');
 
 const ret = spawnSync(
   process.execPath,
-  ['--stack_size=150', __filename, 'async']
+  ['--stack_size=150', __filename, 'async'],
+  { maxBuffer: Infinity }
 );
 assert.strictEqual(ret.status, 0,
                    `EXIT CODE: ${ret.status}, STDERR:\n${ret.stderr}`);

test/parallel/test-child-process-exec-maxbuf.js

@@ -56,6 +56,30 @@ function runChecks(err, stdio, streamName, expected) {
   );
 }
 
+// default value
+{
+  const cmd = `"${process.execPath}" -e "console.log('a'.repeat(200 * 1024))"`;
+
+  cp.exec(
+    cmd,
+    common.mustCall((err, stdout, stderr) => {
+      runChecks(err, { stdout, stderr }, 'stdout', 'a'.repeat(200 * 1024));
+    })
+  );
+}
+
+// default value
+{
+  const cmd =
+    `"${process.execPath}" -e "console.log('a'.repeat(200 * 1024 - 1))"`;
+
+  cp.exec(cmd, common.mustCall((err, stdout, stderr) => {
+    assert.ifError(err);
+    assert.strictEqual(stdout.trim(), 'a'.repeat(200 * 1024 - 1));
+    assert.strictEqual(stderr, '');
+  }));
+}
+
 const unicode = '中文测试'; // length = 4, byte length = 12
 
 {

test/parallel/test-child-process-execfilesync-maxBuffer.js

@@ -0,0 +1,50 @@
+'use strict';
+require('../common');
+
+// This test checks that the maxBuffer option for child_process.spawnFileSync()
+// works as expected.
+
+const assert = require('assert');
+const { execFileSync } = require('child_process');
+const msgOut = 'this is stdout';
+const msgOutBuf = Buffer.from(`${msgOut}\n`);
+
+const args = [
+  '-e',
+  `console.log("${msgOut}");`
+];
+
+// Verify that an error is returned if maxBuffer is surpassed.
+{
+  assert.throws(() => {
+    execFileSync(process.execPath, args, { maxBuffer: 1 });
+  }, (e) => {
+    assert.ok(e, 'maxBuffer should error');
+    assert.strictEqual(e.errno, 'ENOBUFS');
+    // We can have buffers larger than maxBuffer because underneath we alloc 64k
+    // that matches our read sizes.
+    assert.deepStrictEqual(e.stdout, msgOutBuf);
+    return true;
+  });
+}
+
+// Verify that a maxBuffer size of Infinity works.
+{
+  const ret = execFileSync(process.execPath, args, { maxBuffer: Infinity });
+
+  assert.deepStrictEqual(ret, msgOutBuf);
+}
+
+// Default maxBuffer size is 200 * 1024.
+{
+  assert.throws(() => {
+    execFileSync(
+      process.execPath,
+      ['-e', "console.log('a'.repeat(200 * 1024))"]
+    );
+  }, (e) => {
+    assert.ok(e, 'maxBuffer should error');
+    assert.strictEqual(e.errno, 'ENOBUFS');
+    return true;
+  });
+}

test/parallel/test-child-process-execfilesync-maxbuf.js

@@ -34,13 +34,19 @@ const args = [
   assert.deepStrictEqual(ret, msgOutBuf);
 }
 
-// maxBuffer size is Infinity at default.
+// maxBuffer size is 200 * 1024 at default.
 {
-  const ret = execFileSync(
-    process.execPath,
-    ['-e', "console.log('a'.repeat(200 * 1024))"],
-    { encoding: 'utf-8' }
+  assert.throws(
+    () => {
+      execFileSync(
+        process.execPath,
+        ['-e', "console.log('a'.repeat(200 * 1024))"],
+        { encoding: 'utf-8' }
+      );
+    }, (e) => {
+      assert.ok(e, 'maxBuffer should error');
+      assert.strictEqual(e.errno, 'ENOBUFS');
+      return true;
+    }
   );
-
-  assert.ifError(ret.error);
 }

test/parallel/test-child-process-execsync-maxbuf.js

@@ -21,6 +21,8 @@ const args = [
   }, (e) => {
     assert.ok(e, 'maxBuffer should error');
     assert.strictEqual(e.errno, 'ENOBUFS');
+    // We can have buffers larger than maxBuffer because underneath we alloc 64k
+    // that matches our read sizes.
     assert.deepStrictEqual(e.stdout, msgOutBuf);
     return true;
   });
@@ -35,3 +37,23 @@ const args = [
 
   assert.deepStrictEqual(ret, msgOutBuf);
 }
+
+// Default maxBuffer size is 200 * 1024.
+{
+  assert.throws(() => {
+    execSync(`"${process.execPath}" -e "console.log('a'.repeat(200 * 1024))"`);
+  }, (e) => {
+    assert.ok(e, 'maxBuffer should error');
+    assert.strictEqual(e.errno, 'ENOBUFS');
+    return true;
+  });
+}
+
+// Default maxBuffer size is 200 * 1024.
+{
+  const ret = execSync(
+    `"${process.execPath}" -e "console.log('a'.repeat(200 * 1024 - 1))"`
+  );
+
+  assert.deepStrictEqual(ret.toString().trim(), 'a'.repeat(200 * 1024 - 1));
+}

test/parallel/test-child-process-spawnsync-maxbuf.js

@@ -33,10 +33,23 @@ const args = [
   assert.deepStrictEqual(ret.stdout, msgOutBuf);
 }
 
-// maxBuffer size is Infinity at default.
+// Default maxBuffer size is 200 * 1024.
 {
   const args = ['-e', "console.log('a'.repeat(200 * 1024))"];
-  const ret = spawnSync(process.execPath, args, { encoding: 'utf-8' });
+  const ret = spawnSync(process.execPath, args);
+
+  assert.ok(ret.error, 'maxBuffer should error');
+  assert.strictEqual(ret.error.errno, 'ENOBUFS');
+}
+
+// Default maxBuffer size is 200 * 1024.
+{
+  const args = ['-e', "console.log('a'.repeat(200 * 1024 - 1))"];
+  const ret = spawnSync(process.execPath, args);
 
   assert.ifError(ret.error);
+  assert.deepStrictEqual(
+    ret.stdout.toString().trim(),
+    'a'.repeat(200 * 1024 - 1)
+  );
 }

test/parallel/test-tick-processor-arguments.js

@@ -26,7 +26,7 @@ assert(logfile);
 const { stdout } = spawnSync(
   process.execPath,
   [ '--prof-process', '--preprocess', logfile ],
-  { cwd: tmpdir.path, encoding: 'utf8' });
+  { cwd: tmpdir.path, encoding: 'utf8', maxBuffer: Infinity });
 
 // Make sure that the result is valid JSON.
 JSON.parse(stdout);