[v14.x backport] stream: simpler and faster Readable async iterator

lib/_stream_readable.js

@@ -27,6 +27,7 @@ const {
   NumberIsNaN,
   ObjectDefineProperties,
   ObjectSetPrototypeOf,
+  Promise,
   Set,
   SymbolAsyncIterator,
   Symbol
@@ -59,11 +60,11 @@ const kPaused = Symbol('kPaused');
 
 // Lazy loaded to improve the startup performance.
 let StringDecoder;
-let createReadableStreamAsyncIterator;
 let from;
 
 ObjectSetPrototypeOf(Readable.prototype, Stream.prototype);
 ObjectSetPrototypeOf(Readable, Stream);
+function nop() {}
 
 const { errorOrDestroy } = destroyImpl;
 
@@ -1075,13 +1076,86 @@ Readable.prototype.wrap = function(stream) {
 };
 
 Readable.prototype[SymbolAsyncIterator] = function() {
-  if (createReadableStreamAsyncIterator === undefined) {
-    createReadableStreamAsyncIterator =
-      require('internal/streams/async_iterator');
+  let stream = this;
+
+  if (typeof stream.read !== 'function') {
+    // v1 stream
+    const src = stream;
+    stream = new Readable({
+      objectMode: true,
+      destroy(err, callback) {
+        destroyImpl.destroyer(src, err);
+        callback(err);
+      }
+    }).wrap(src);
   }
-  return createReadableStreamAsyncIterator(this);
+
+  const iter = createAsyncIterator(stream);
+  iter.stream = stream;
+  return iter;
 };
 
+async function* createAsyncIterator(stream) {
+  let callback = nop;
+
+  function next(resolve) {
+    if (this === stream) {
+      callback();
+      callback = nop;
+    } else {
+      callback = resolve;
+    }
+  }
+
+  const state = stream._readableState;
+
+  let error = state.errored;
+  let errorEmitted = state.errorEmitted;
+  let endEmitted = state.endEmitted;
+  let closeEmitted = state.closeEmitted;
+
+  stream
+    .on('readable', next)
+    .on('error', function(err) {
+      error = err;
+      errorEmitted = true;
+      next.call(this);
+    })
+    .on('end', function() {
+      endEmitted = true;
+      next.call(this);
+    })
+    .on('close', function() {
+      closeEmitted = true;
+      next.call(this);
+    });
+
+  try {
+    while (true) {
+      const chunk = stream.destroyed ? null : stream.read();
+      if (chunk !== null) {
+        yield chunk;
+      } else if (errorEmitted) {
+        throw error;
+      } else if (endEmitted) {
+        break;
+      } else if (closeEmitted) {
+        break;
+      } else {
+        await new Promise(next);
+      }
+    }
+  } catch (err) {
+    destroyImpl.destroyer(stream, err);
+    throw err;
+  } finally {
+    if (state.autoDestroy || !endEmitted) {
+      // TODO(ronag): ERR_PREMATURE_CLOSE?
+      destroyImpl.destroyer(stream, null);
+    }
+  }
+}
+
 // Making it explicit these properties are not enumerable
 // because otherwise some prototype manipulation in
 // userland will fail.

lib/internal/streams/destroy.js

@@ -123,6 +123,7 @@ function undestroy() {
 
   if (w) {
     w.closed = false;
+    w.closeEmitted = false;
     w.destroyed = false;
     w.errored = null;
     w.ended = false;

lib/internal/streams/pipeline.js

@@ -23,7 +23,7 @@ const {
 
 let EE;
 let PassThrough;
-let createReadableStreamAsyncIterator;
+let Readable;
 
 function destroyer(stream, reading, writing, callback) {
   callback = once(callback);
@@ -113,11 +113,10 @@ function makeAsyncIterable(val) {
 }
 
 async function* fromReadable(val) {
-  if (!createReadableStreamAsyncIterator) {
-    createReadableStreamAsyncIterator =
-      require('internal/streams/async_iterator');
+  if (!Readable) {
+    Readable = require('_stream_readable');
   }
-  yield* createReadableStreamAsyncIterator(val);
+  yield* Readable.prototype[SymbolAsyncIterator].call(val);
 }
 
 async function pump(iterable, writable, finish) {

node.gyp

@@ -222,7 +222,6 @@
       'lib/internal/worker/js_transferable.js',
       'lib/internal/watchdog.js',
       'lib/internal/streams/lazy_transform.js',
-      'lib/internal/streams/async_iterator.js',
       'lib/internal/streams/buffer_list.js',
       'lib/internal/streams/duplexpair.js',
       'lib/internal/streams/from.js',