stream: add isErrored helper

Refs: nodejs/undici#1134

Author: ronag

doc/api/stream.md

@@ -2225,6 +2225,19 @@ added: v16.8.0
 
 Returns whether the stream has been read from or cancelled.
 
+### `stream.Readable.isErrored(stream)`
+
+<!-- YAML
+added: v16.8.0
+-->
+
+> Stability: 1 - Experimental
+
+* `stream` {stream.Readable|ReadableStream}
+* Returns: `boolean`
+
+Returns whether the stream has been errored.
+
 ### `stream.Readable.toWeb(streamReadable)`
 
 <!-- YAML

lib/internal/streams/utils.js

@@ -239,16 +239,29 @@ function willEmitClose(stream) {
 
 function isDisturbed(stream) {
   return !!(stream && (
-    stream.readableDidRead ||
-    stream.readableAborted ||
-    stream[kIsDisturbed]
+    stream[kIsDisturbed] ??
+    (stream.readableDidRead || stream.readableAborted)
+  ));
+}
+
+function isErrored(stream) {
+  return !!(stream && (
+    stream[kIsErrored] ??
+    stream.readableErrored ??
+    stream.writableErrored ??
+    stream._readableState?.errorEmitted ??
+    stream._writableState?.errorEmitted ??
+    stream._readableState?.errored ??
+    stream._writableState?.errored
   ));
 }
 
 module.exports = {
   kDestroyed,
   isDisturbed,
+  isErrored,
   kIsDisturbed,
+  kIsErrored,
   isClosed,
   isDestroyed,
   isDuplexNodeStream,

lib/internal/webstreams/readablestream.js

@@ -241,6 +241,10 @@ class ReadableStream {
     return this[kState].disturbed;
   }
 
+  get [kIsErrored]() {
+    return this[kState].state === 'errored';
+  }
+
   /**
    * @readonly
    * @type {boolean}

lib/stream.js

@@ -39,6 +39,7 @@ const promises = require('stream/promises');
 
 const Stream = module.exports = require('internal/streams/legacy').Stream;
 Stream.isDisturbed = require('internal/streams/utils').isDisturbed;
+Stream.isErrored = require('internal/streams/utils').isErrored;
 Stream.Readable = require('internal/streams/readable');
 Stream.Writable = require('internal/streams/writable');
 Stream.Duplex = require('internal/streams/duplex');

test/parallel/test-stream-readable-didRead.js

@@ -1,15 +1,18 @@
 'use strict';
 const common = require('../common');
 const assert = require('assert');
-const { isDisturbed, Readable } = require('stream');
+const { isDisturbed, isErrored, Readable } = require('stream');
 
 function noop() {}
 
 function check(readable, data, fn) {
   assert.strictEqual(readable.readableDidRead, false);
   assert.strictEqual(isDisturbed(readable), false);
+  assert.strictEqual(isErrored(readable), false);
   if (data === -1) {
-    readable.on('error', common.mustCall());
+    readable.on('error', common.mustCall(() => {
+      assert.strictEqual(isErrored(readable), true)
+    }));
     readable.on('data', common.mustNotCall());
     readable.on('end', common.mustNotCall());
   } else {

test/parallel/test-whatwg-readablestream.js

@@ -1572,3 +1572,20 @@ class Source {
     isDisturbed(stream, true);
   })().then(common.mustCall());
 }
+
+
+{
+  const stream = new ReadableStream({
+    start(controller) {
+      controller.error(new Error());
+    },
+    pull: common.mustNotCall(),
+  });
+
+  const reader = stream.getReader();
+  (async () => {
+    isErrored(stream, false);
+    await reader.read();
+    isErrored(stream, true);
+  })().then(common.mustCall());
+}