stream: use readableEncoding public api for child_process

PR-URL: https://github.com/nodejs/node/pull/28548
Refs: https://github.com/nodejs/node/issues/445
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

doc/api/stream.md

@@ -1085,6 +1085,16 @@ added: v11.4.0
 
 Is `true` if it is safe to call [`readable.read()`][stream-read].
 
+##### readable.readableEncoding
+<!-- YAML
+added: REPLACEME
+-->
+
+* {null|string}
+
+Getter for the property `encoding` of a given `Readable` stream. The `encoding`
+property can be set using the [`readable.setEncoding()`][] method.
+
 ##### readable.readableHighWaterMark
 <!-- YAML
 added: v9.3.0
@@ -2655,6 +2665,7 @@ contain multi-byte characters.
 [`process.stdin`]: process.html#process_process_stdin
 [`process.stdout`]: process.html#process_process_stdout
 [`readable.push('')`]: #stream_readable_push
+[`readable.setEncoding()`]: #stream_readable_setencoding_encoding
 [`stream.Readable.from()`]: #stream_stream_readable_from_iterable_options
 [`stream.cork()`]: #stream_writable_cork
 [`stream.finished()`]: #stream_stream_finished_stream_options_callback

lib/_stream_readable.js

@@ -1075,6 +1075,13 @@ Object.defineProperty(Readable.prototype, 'readableObjectMode', {
   }
 });
 
+Object.defineProperty(Readable.prototype, 'readableEncoding', {
+  enumerable: false,
+  get() {
+    return this._readableState ? this._readableState.encoding : null;
+  }
+});
+
 // Pluck off n bytes from an array of buffers.
 // Length is the combined lengths of all the buffers in the list.
 // This function is designed to be inlinable, so please take care when making

lib/child_process.js

@@ -266,8 +266,7 @@ function execFile(file /* , args, options, callback */) {
     if (encoding ||
       (
         child.stdout &&
-        child.stdout._readableState &&
-        child.stdout._readableState.encoding
+        child.stdout.readableEncoding
       )) {
       stdout = _stdout.join('');
     } else {
@@ -276,8 +275,7 @@ function execFile(file /* , args, options, callback */) {
     if (encoding ||
       (
         child.stderr &&
-        child.stderr._readableState &&
-        child.stderr._readableState.encoding
+        child.stderr.readableEncoding
       )) {
       stderr = _stderr.join('');
     } else {
@@ -344,7 +342,7 @@ function execFile(file /* , args, options, callback */) {
       child.stdout.setEncoding(encoding);
 
     child.stdout.on('data', function onChildStdout(chunk) {
-      const encoding = child.stdout._readableState.encoding;
+      const encoding = child.stdout.readableEncoding;
       const length = encoding ?
         Buffer.byteLength(chunk, encoding) :
         chunk.length;
@@ -367,7 +365,7 @@ function execFile(file /* , args, options, callback */) {
       child.stderr.setEncoding(encoding);
 
     child.stderr.on('data', function onChildStderr(chunk) {
-      const encoding = child.stderr._readableState.encoding;
+      const encoding = child.stderr.readableEncoding;
       const length = encoding ?
         Buffer.byteLength(chunk, encoding) :
         chunk.length;

test/parallel/test-stream2-basic.js

@@ -422,14 +422,26 @@ class TestWriter extends EE {
   assert.strictEqual(r, r2);
 }
 
+{
+  // Verify readableEncoding property
+  assert(R.prototype.hasOwnProperty('readableEncoding'));
+
+  const r = new R({ encoding: 'utf8' });
+  assert.strictEqual(r.readableEncoding, 'utf8');
+}
+
 {
   // Verify readableObjectMode property
+  assert(R.prototype.hasOwnProperty('readableObjectMode'));
+
   const r = new R({ objectMode: true });
   assert.strictEqual(r.readableObjectMode, true);
 }
 
 {
   // Verify writableObjectMode property
+  assert(W.prototype.hasOwnProperty('writableObjectMode'));
+
   const w = new W({ objectMode: true });
   assert.strictEqual(w.writableObjectMode, true);
 }