stream: simplify isBuf

PR-URL: #31067
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Denys Otrishko <shishugi@gmail.com>

lib/_stream_writable.js

@@ -313,7 +313,7 @@ Writable.prototype.write = function(chunk, encoding, cb) {
     writeAfterEnd(this, cb);
   else if (isBuf || validChunk(this, state, chunk, cb)) {
     state.pendingcb++;
-    ret = writeOrBuffer(this, state, isBuf, chunk, encoding, cb);
+    ret = writeOrBuffer(this, state, chunk, encoding, cb);
   }
 
   return ret;
@@ -357,15 +357,6 @@ ObjectDefineProperty(Writable.prototype, 'writableBuffer', {
   }
 });
 
-function decodeChunk(state, chunk, encoding) {
-  if (!state.objectMode &&
-      state.decodeStrings !== false &&
-      typeof chunk === 'string') {
-    chunk = Buffer.from(chunk, encoding);
-  }
-  return chunk;
-}
-
 ObjectDefineProperty(Writable.prototype, 'writableEnded', {
   // Making it explicit this property is not enumerable
   // because otherwise some prototype manipulation in
@@ -399,14 +390,13 @@ ObjectDefineProperty(Writable.prototype, 'writableCorked', {
 // If we're already writing something, then just put this
 // in the queue, and wait our turn.  Otherwise, call _write
 // If we return false, then we need a drain event, so set that flag.
-function writeOrBuffer(stream, state, isBuf, chunk, encoding, cb) {
-  if (!isBuf) {
-    var newChunk = decodeChunk(state, chunk, encoding);
-    if (chunk !== newChunk) {
-      isBuf = true;
-      encoding = 'buffer';
-      chunk = newChunk;
-    }
+function writeOrBuffer(stream, state, chunk, encoding, cb) {
+  if (!state.objectMode &&
+      state.decodeStrings !== false &&
+      encoding !== 'buffer' &&
+      typeof chunk === 'string') {
+    chunk = Buffer.from(chunk, encoding);
+    encoding = 'buffer';
   }
   const len = state.objectMode ? 1 : chunk.length;
 
@@ -422,7 +412,6 @@ function writeOrBuffer(stream, state, isBuf, chunk, encoding, cb) {
     state.lastBufferedRequest = {
       chunk,
       encoding,
-      isBuf,
       callback: cb,
       next: null
     };
@@ -558,7 +547,7 @@ function clearBuffer(stream, state) {
     var allBuffers = true;
     while (entry) {
       buffer[count] = entry;
-      if (!entry.isBuf)
+      if (entry.encoding !== 'buffer')
         allBuffers = false;
       entry = entry.next;
       count += 1;