stream: avoid additional validation for Buffers

These changes result in ~50% improvement in the included benchmark.
PR-URL: #10580
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: mscdex

benchmark/streams/writable-manywrites.js

@@ -0,0 +1,23 @@
+'use strict';
+
+constcommon=require('../common');
+constWritable=require('stream').Writable;
+
+constbench=common.createBenchmark(main,{
+n: [2e6]
+});
+
+functionmain(conf){
+constn=+conf.n;
+constb=Buffer.allocUnsafe(1024);
+consts=newWritable();
+s._write=function(chunk,encoding,cb){
+cb();
+};
+
+bench.start();
+for(vark=0;k<n;++k){
+s.write(b);
+}
+bench.end(n);
+}

lib/_stream_writable.js

@@ -196,23 +196,18 @@ function writeAfterEnd(stream, cb) {
 process.nextTick(cb,er);
 }
 
-// If we get something that is not a buffer, string, null, or undefined,
-// and we're not in objectMode, then that's an error.
-// Otherwise stream chunks are all considered to be of length=1, and the
-// watermarks determine how many objects to keep in the buffer, rather than
-// how many bytes or characters.
+// Checks that a user-supplied chunk is valid, especially for the particular
+// mode the stream is in. Currently this means that `null` is never accepted
+// and undefined/non-string values are only allowed in object mode.
 functionvalidChunk(stream,state,chunk,cb){
 varvalid=true;
 varer=false;
-// Always throw error if a null is written
-// if we are not in object mode then throw
-// if it is not a buffer, string, or undefined.
+
 if(chunk===null){
 er=newTypeError('May not write null values to stream');
-}elseif(!(chunkinstanceofBuffer)&&
-typeofchunk!=='string'&&
-chunk!==undefined&&
-!state.objectMode){
+}elseif(typeofchunk!=='string'&&
+chunk!==undefined&&
+!state.objectMode){
 er=newTypeError('Invalid non-string/buffer chunk');
 }
 if(er){
@@ -226,13 +221,14 @@ function validChunk(stream, state, chunk, cb) {
 Writable.prototype.write=function(chunk,encoding,cb){
 varstate=this._writableState;
 varret=false;
+varisBuf=(chunkinstanceofBuffer);
 
 if(typeofencoding==='function'){
 cb=encoding;
 encoding=null;
 }
 
-if(chunkinstanceofBuffer)
+if(isBuf)
 encoding='buffer';
 elseif(!encoding)
 encoding=state.defaultEncoding;
@@ -242,9 +238,9 @@ Writable.prototype.write = function(chunk, encoding, cb) {
 
 if(state.ended)
 writeAfterEnd(this,cb);
-elseif(validChunk(this,state,chunk,cb)){
+elseif(isBuf||validChunk(this,state,chunk,cb)){
 state.pendingcb++;
-ret=writeOrBuffer(this,state,chunk,encoding,cb);
+ret=writeOrBuffer(this,state,isBuf,chunk,encoding,cb);
 }
 
 returnret;
@@ -293,11 +289,12 @@ function decodeChunk(state, chunk, encoding) {
 // 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.
-functionwriteOrBuffer(stream,state,chunk,encoding,cb){
-chunk=decodeChunk(state,chunk,encoding);
-
-if(chunkinstanceofBuffer)
-encoding='buffer';
+functionwriteOrBuffer(stream,state,isBuf,chunk,encoding,cb){
+if(!isBuf){
+chunk=decodeChunk(state,chunk,encoding);
+if(chunkinstanceofBuffer)
+encoding='buffer';
+}
 varlen=state.objectMode ? 1 : chunk.length;
 
 state.length+=len;