child_process: fix exec set stdout.setEncoding

cp.exec decide to use `_stdout`(_stdout is string) or
`Buffer.concat(_stdout)`(_stdout is buffer array) by options.encoding.
but std(out|err) encoding can be changed. If encoding is changed to
not null, `_stdout` will become string, and `Buffer.concat(_stdout)`
will throw TypeError. This patch will fix it, use
options.encoding and `std(out|err)._readableState.encoding`.

PR-URL: https://github.com/nodejs/node/pull/18976
Fixes: https://github.com/nodejs/node/issues/18969
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

3 files changed, 60 insertions, 0 deletions

diff --git a/test/parallel/test-child-process-exec-maxBuffer.js b/test/parallel/test-child-process-exec-maxBuffer.js
index 4a65ccf5be..94545e719b 100644
--- a/test/parallel/test-child-process-exec-maxBuffer.js
+++ b/test/parallel/test-child-process-exec-maxBuffer.js
@@ -41,3 +41,25 @@ const unicode = '中文测试'; // length = 4, byte length = 12
 
   cp.exec(cmd, { maxBuffer: 10 }, checkFactory('stderr'));
 }
+
+{
+  const cmd = `"${process.execPath}" -e "console.log('${unicode}');"`;
+
+  const child = cp.exec(
+    cmd,
+    { encoding: null, maxBuffer: 10 },
+    checkFactory('stdout'));
+
+  child.stdout.setEncoding('utf-8');
+}
+
+{
+  const cmd = `"${process.execPath}" -e "console.error('${unicode}');"`;
+
+  const child = cp.exec(
+    cmd,
+    { encoding: null, maxBuffer: 10 },
+    checkFactory('stderr'));
+
+  child.stderr.setEncoding('utf-8');
+}
diff --git a/test/parallel/test-child-process-exec-std-encoding.js b/test/parallel/test-child-process-exec-std-encoding.js
new file mode 100644
index 0000000000..11cb66cf42
--- /dev/null
+++ b/test/parallel/test-child-process-exec-std-encoding.js
@@ -0,0 +1,23 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const cp = require('child_process');
+const stdoutData = 'foo';
+const stderrData = 'bar';
+const expectedStdout = `${stdoutData}\n`;
+const expectedStderr = `${stderrData}\n`;
+
+if (process.argv[2] === 'child') {
+  // The following console calls are part of the test.
+  console.log(stdoutData);
+  console.error(stderrData);
+} else {
+  const cmd = `"${process.execPath}" "${__filename}" child`;
+  const child = cp.exec(cmd, common.mustCall((err, stdout, stderr) => {
+    assert.ifError(err);
+    assert.strictEqual(stdout, expectedStdout);
+    assert.strictEqual(stderr, expectedStderr);
+  }));
+  child.stdout.setEncoding('utf-8');
+  child.stderr.setEncoding('utf-8');
+}
diff --git a/test/parallel/test-stream-readable-setEncoding-null.js b/test/parallel/test-stream-readable-setEncoding-null.js
new file mode 100644
index 0000000000..b95b26bb79
--- /dev/null
+++ b/test/parallel/test-stream-readable-setEncoding-null.js
@@ -0,0 +1,15 @@
+'use strict';
+
+require('../common');
+const assert = require('assert');
+const { Readable } = require('stream');
+
+
+{
+  const readable = new Readable({ encoding: 'hex' });
+  assert.strictEqual(readable._readableState.encoding, 'hex');
+
+  readable.setEncoding(null);
+
+  assert.strictEqual(readable._readableState.encoding, 'utf8');
+}