stream: inline needMoreData function

Inline the needMoreData function since it has only one call place.
Update the related comment.
Add a test for the edge case where HWM=0 and state.length=0.
Add a test for ReadableStream.read(n) method's edge case where
n, HWM and state.length are all zero.
This proves that there is no easy way to simplify the check at
https://github.com/nodejs/node/blob/master/lib/_stream_readable.js#L440Fixes: #19893
Refs: #19896
PR-URL: #21009
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Lance Ball <lball@redhat.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

Author: kodemill

lib/_stream_readable.js

@@ -270,7 +270,11 @@ function readableAddChunk(stream, chunk, encoding, addToFront, skipChunkCheck) {
 }
 }
 
-returnneedMoreData(state);
+// We can push more data if we are below the highWaterMark.
+// Also, if we have no data yet, we can stand some more bytes.
+// This is to work around cases where hwm=0, such as the repl.
+return!state.ended&&
+(state.length<state.highWaterMark||state.length===0);
 }
 
 functionaddChunk(stream,state,chunk,addToFront){
@@ -304,19 +308,6 @@ function chunkInvalid(state, chunk) {
 }
 
 
-// We can push more data if we are below the highWaterMark.
-// Also, if we have no data yet, we can stand some
-// more bytes. This is to work around cases where hwm=0,
-// such as the repl. Also, if the push() triggered a
-// readable event, and the user called read(largeNumber) such that
-// needReadable was set, then we ought to push more, so that another
-// 'readable' event will be triggered.
-functionneedMoreData(state){
-return!state.ended&&
-(state.length<state.highWaterMark||
-state.length===0);
-}
-
 Readable.prototype.isPaused=function(){
 returnthis._readableState.flowing===false;
 };

test/parallel/test-streams-highwatermark.js

@@ -1,31 +1,58 @@
 'use strict';
 constcommon=require('../common');
 
-// This test ensures that the stream implementation correctly handles values
-// for highWaterMark which exceed the range of signed 32 bit integers and
-// rejects invalid values.
-
 constassert=require('assert');
 conststream=require('stream');
 
-// This number exceeds the range of 32 bit integer arithmetic but should still
-// be handled correctly.
-constovfl=Number.MAX_SAFE_INTEGER;
-
-constreadable=stream.Readable({highWaterMark: ovfl});
-assert.strictEqual(readable._readableState.highWaterMark,ovfl);
-
-constwritable=stream.Writable({highWaterMark: ovfl});
-assert.strictEqual(writable._writableState.highWaterMark,ovfl);
-
-for(constinvalidHwmof[true,false,'5',{},-5,NaN]){
-for(consttypeof[stream.Readable,stream.Writable]){
-common.expectsError(()=>{
-type({highWaterMark: invalidHwm});
-},{
-type: TypeError,
-code: 'ERR_INVALID_OPT_VALUE',
-message: `The value "${invalidHwm}" is invalid for option "highWaterMark"`
-});
+{
+// This test ensures that the stream implementation correctly handles values
+// for highWaterMark which exceed the range of signed 32 bit integers and
+// rejects invalid values.
+
+// This number exceeds the range of 32 bit integer arithmetic but should still
+// be handled correctly.
+constovfl=Number.MAX_SAFE_INTEGER;
+
+constreadable=stream.Readable({highWaterMark: ovfl});
+assert.strictEqual(readable._readableState.highWaterMark,ovfl);
+
+constwritable=stream.Writable({highWaterMark: ovfl});
+assert.strictEqual(writable._writableState.highWaterMark,ovfl);
+
+for(constinvalidHwmof[true,false,'5',{},-5,NaN]){
+for(consttypeof[stream.Readable,stream.Writable]){
+common.expectsError(()=>{
+type({highWaterMark: invalidHwm});
+},{
+type: TypeError,
+code: 'ERR_INVALID_OPT_VALUE',
+message:
+`The value "${invalidHwm}" is invalid for option "highWaterMark"`
+});
+}
+}
+}
+
+{
+// This test ensures that the push method's implementation
+// correctly handles the edge case where the highWaterMark and
+// the state.length are both zero
+
+constreadable=stream.Readable({highWaterMark: 0});
+
+for(leti=0;i<3;i++){
+constneedMoreData=readable.push();
+assert.strictEqual(needMoreData,true);
 }
 }
+
+{
+// This test ensures that the read(n) method's implementation
+// correctly handles the edge case where the highWaterMark, state.length
+// and n are all zero
+
+constreadable=stream.Readable({highWaterMark: 0});
+
+readable._read=common.mustCall();
+readable.read(0);
+}