stream: add isReadable helper

doc/api/stream.md

@@ -2238,6 +2238,19 @@ added: REPLACEME
 
 Returns whether the stream has encountered an error.
 
+### `stream.isReadable(stream)`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1 - Experimental
+
+* `stream`{Readable|Duplex|ReadableStream}
+* Returns:{boolean}
+
+Returns whether the stream is readable.
+
 ### `stream.Readable.toWeb(streamReadable)`
 
 <!-- YAML

lib/internal/streams/utils.js

@@ -8,6 +8,7 @@ const{
 
 const kDestroyed = Symbol('kDestroyed');
 const kIsErrored = Symbol('kIsErrored');
+const kIsReadable = Symbol('kIsReadable');
 const kIsDisturbed = Symbol('kIsDisturbed');
 
 function isReadableNodeStream(obj, strict = false){
@@ -116,6 +117,7 @@ function isReadableFinished(stream, strict){
 }
 
 function isReadable(stream){
+ if (stream && stream[kIsReadable] != null) return stream[kIsReadable];
  const r = isReadableNodeStream(stream);
  if (r === null || typeof stream?.readable !== 'boolean') return null;
  if (isDestroyed(stream)) return false;
@@ -260,15 +262,16 @@ function isErrored(stream){
 module.exports ={
  kDestroyed,
  isDisturbed,
- isErrored,
  kIsDisturbed,
+ isErrored,
  kIsErrored,
+ isReadable,
+ kIsReadable,
  isClosed,
  isDestroyed,
  isDuplexNodeStream,
  isFinished,
  isIterable,
- isReadable,
  isReadableNodeStream,
  isReadableEnded,
  isReadableFinished,

lib/internal/webstreams/readablestream.js

@@ -83,6 +83,7 @@ const{
 const{
  kIsDisturbed,
  kIsErrored,
+ kIsReadable,
 } = require('internal/streams/utils');
 
 const{
@@ -246,6 +247,10 @@ class ReadableStream{
  return this[kState].state === 'errored'
  }
 
+ get [kIsReadable](){
+ return this[kState].state === 'readable'
+ }
+
  /**
  * @readonly
  * @type{boolean}

lib/stream.js

@@ -41,6 +41,7 @@ const utils = require('internal/streams/utils');
 const Stream = module.exports = require('internal/streams/legacy').Stream;
 Stream.isDisturbed = utils.isDisturbed;
 Stream.isErrored = utils.isErrored;
+Stream.isReadable = utils.isReadable;
 Stream.Readable = require('internal/streams/readable');
 Stream.Writable = require('internal/streams/writable');
 Stream.Duplex = require('internal/streams/duplex');

test/parallel/test-whatwg-readablestream.js

@@ -2,7 +2,7 @@
 'use strict'
 
 const common = require('../common');
-const{isDisturbed, isErrored } = require('stream');
+const{isDisturbed, isErrored, isReadable } = require('stream');
 const assert = require('assert');
 const{
  isPromise,
@@ -1573,7 +1573,6 @@ class Source{
  })().then(common.mustCall());
 }
 
-
 {
  const stream = new ReadableStream({
  pull: common.mustCall((controller) =>{
@@ -1588,3 +1587,18 @@ class Source{
  isErrored(stream, true);
  })().then(common.mustCall());
 }
+
+{
+ const stream = new ReadableStream({
+ pull: common.mustCall((controller) =>{
+ controller.error(new Error());
+ }),
+ });
+
+ const reader = stream.getReader();
+ (async () =>{
+ isReadable(stream, true);
+ await reader.read().catch(common.mustCall());
+ isReadable(stream, false);
+ })().then(common.mustCall());
+}