stream: refactor writable _write

lib/internal/streams/writable.js

@@ -443,22 +443,21 @@ Writable.prototype.pipe = function() {
 function _write(stream, chunk, encoding, cb) {
   const state = stream._writableState;
 
-  if (typeof encoding === 'function') {
-    cb = encoding;
-    encoding = null;
-  }
-
-  if (!encoding)
-    encoding = (state[kState] & kDefaultUTF8Encoding) !== 0 ? 'utf8' : state[kDefaultEncodingValue];
-  else if (encoding !== 'buffer' && !Buffer.isEncoding(encoding))
-    throw new ERR_UNKNOWN_ENCODING(encoding);
-
-  if (cb == null || typeof cb !== 'function')
+  if (cb == null || typeof cb !== 'function') {
     cb = nop;
+  }
 
   if (chunk === null) {
     throw new ERR_STREAM_NULL_VALUES();
-  } else if ((state[kState] & kObjectMode) === 0) {
+  }
+
+  if ((state[kState] & kObjectMode) === 0) {
+    if (!encoding) {
+      encoding = (state[kState] & kDefaultUTF8Encoding) !== 0 ? 'utf8' : state.defaultEncoding;
+    } else if (encoding !== 'buffer' && !Buffer.isEncoding(encoding)) {
+      throw new ERR_UNKNOWN_ENCODING(encoding);
+    }
+
     if (typeof chunk === 'string') {
       if ((state[kState] & kDecodeStrings) !== 0) {
         chunk = Buffer.from(chunk, encoding);
@@ -487,11 +486,17 @@ function _write(stream, chunk, encoding, cb) {
     errorOrDestroy(stream, err, true);
     return err;
   }
+
   state.pendingcb++;
   return writeOrBuffer(stream, state, chunk, encoding, cb);
 }
 
 Writable.prototype.write = function(chunk, encoding, cb) {
+  if (encoding != null && typeof encoding === 'function') {
+    cb = encoding;
+    encoding = null;
+  }
+
   return _write(this, chunk, encoding, cb) === true;
 };
 

test/parallel/test-stream-uint8array.js

@@ -38,7 +38,7 @@ const GHI = new Uint8Array([0x47, 0x48, 0x49]);
       assert(!(chunk instanceof Buffer));
       assert(chunk instanceof Uint8Array);
       assert.strictEqual(chunk, ABC);
-      assert.strictEqual(encoding, 'utf8');
+      assert.strictEqual(encoding, undefined);
       cb();
     })
   });