child_process: measure buffer length in bytes

This change fixes a known issue where `maxBuffer` limits by characters
rather than bytes. Benchmark added to confirm no performance regression
occurs with this change.

PR-URL: https://github.com/nodejs/node/pull/6764
Fixes: https://github.com/nodejs/node/issues/1901
Reviewed-By: Brian White <mscdex@mscdex.net>

2 files changed, 16 insertions, 2 deletions

diff --git a/test/parallel/test-child-process-maxBuffer-stderr.js b/test/parallel/test-child-process-maxBuffer-stderr.js
new file mode 100644
index 0000000000..ecaea8b152
--- /dev/null
+++ b/test/parallel/test-child-process-maxBuffer-stderr.js
@@ -0,0 +1,15 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const cp = require('child_process');
+const unicode = '中文测试'; // Length = 4, Byte length = 13
+
+if (process.argv[2] === 'child') {
+  console.error(unicode);
+} else {
+  const cmd = `${process.execPath} ${__filename} child`;
+
+  cp.exec(cmd, {maxBuffer: 10}, common.mustCall((err, stdout, stderr) => {
+    assert.strictEqual(err.message, 'stderr maxBuffer exceeded');
+  }));
+}
diff --git a/test/known_issues/test-child-process-max-buffer.js b/test/parallel/test-child-process-maxBuffer-stdout.js
index 14a344c706..122dc499f4 100644
--- a/test/known_issues/test-child-process-max-buffer.js
+++ b/test/parallel/test-child-process-maxBuffer-stdout.js
@@ -1,5 +1,4 @@
 'use strict';
-// Refs: https://github.com/nodejs/node/issues/1901
 const common = require('../common');
 const assert = require('assert');
 const cp = require('child_process');
@@ -10,7 +9,7 @@ if (process.argv[2] === 'child') {
 } else {
   const cmd = `${process.execPath} ${__filename} child`;
 
-  cp.exec(cmd, { maxBuffer: 10 }, common.mustCall((err, stdout, stderr) => {
+  cp.exec(cmd, {maxBuffer: 10}, common.mustCall((err, stdout, stderr) => {
     assert.strictEqual(err.message, 'stdout maxBuffer exceeded');
   }));
 }