[v12.x backport] stream: remove ambiguous code

PR-URL: nodejs#29664
Reviewed-By: Minwoo Jung <minwoo@nodesource.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

lib/internal/streams/end-of-stream.js

@@ -28,26 +28,28 @@ function eos(stream, opts, callback) {
 
   callback = once(callback);
 
-  let readable = opts.readable || (opts.readable !== false && stream.readable);
-  let writable = opts.writable || (opts.writable !== false && stream.writable);
+  const readable = opts.readable ||
+    (opts.readable !== false && stream.readable);
+  const writable = opts.writable ||
+    (opts.writable !== false && stream.writable);
 
   const onlegacyfinish = () => {
     if (!stream.writable) onfinish();
   };
 
   let writableEnded = stream._writableState && stream._writableState.finished;
   const onfinish = () => {
-    writable = false;
     writableEnded = true;
     if (!readable) callback.call(stream);
+    writableFinished = true;
+    if (!readable || readableEnded) callback.call(stream);
   };
 
   let readableEnded = stream.readableEnded ||
     (stream._readableState && stream._readableState.endEmitted);
   const onend = () => {
-    readable = false;
     readableEnded = true;
-    if (!writable) callback.call(stream);
+    if (!writable || writableFinished) callback.call(stream);
   };
 
   const onerror = (err) => {