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#L440

Fixes: https://github.com/nodejs/node/issues/19893
Refs: https://github.com/nodejs/node/pull/19896

PR-URL: https://github.com/nodejs/node/pull/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>

1 files changed, 5 insertions, 14 deletions

diff --git a/lib/_stream_readable.js b/lib/_stream_readable.js
index a8e52f5f1d..31b129facd 100644
--- a/lib/_stream_readable.js
+++ b/lib/_stream_readable.js
@@ -270,7 +270,11 @@ function readableAddChunk(stream, chunk, encoding, addToFront, skipChunkCheck) {
     }
   }
 
-  return needMoreData(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);
 }
 
 function addChunk(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.
-function needMoreData(state) {
-  return !state.ended &&
-         (state.length < state.highWaterMark ||
-          state.length === 0);
-}
-
 Readable.prototype.isPaused = function() {
   return this._readableState.flowing === false;
 };