stream: make Readable.from performance better

PR-URL: #37609
Reviewed-By: Robert Nagy <ronagy@icloud.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

benchmark/streams/readable-from.js

@@ -0,0 +1,26 @@
+'use strict';
+
+const common = require('../common');
+const Readable = require('stream').Readable;
+
+const bench = common.createBenchmark(main, {
+  n: [1e7],
+});
+
+async function main({ n }) {
+  const arr = [];
+  for (let i = 0; i < n; i++) {
+    arr.push(`${i}`);
+  }
+
+  const s = new Readable.from(arr);
+
+  bench.start();
+  s.on('data', (data) => {
+    // eslint-disable-next-line no-unused-expressions
+    data;
+  });
+  s.on('close', () => {
+    bench.end(n);
+  });
+}

lib/internal/streams/from.js

@@ -3,7 +3,7 @@
 const {
   PromisePrototypeThen,
   SymbolAsyncIterator,
-  SymbolIterator
+  SymbolIterator,
 } = primordials;
 const { Buffer } = require('buffer');
 
@@ -25,18 +25,22 @@ function from(Readable, iterable, opts) {
     });
   }
 
-  if (iterable && iterable[SymbolAsyncIterator])
+  let isAsync = false;
+  if (iterable && iterable[SymbolAsyncIterator]) {
+    isAsync = true;
     iterator = iterable[SymbolAsyncIterator]();
-  else if (iterable && iterable[SymbolIterator])
+  } else if (iterable && iterable[SymbolIterator]) {
+    isAsync = false;
     iterator = iterable[SymbolIterator]();
-  else
+  } else {
     throw new ERR_INVALID_ARG_TYPE('iterable', ['Iterable'], iterable);
+  }
 
   const readable = new Readable({
     objectMode: true,
     highWaterMark: 1,
     // TODO(ronag): What options should be allowed?
-    ...opts
+    ...opts,
   });
 
   // Flag to protect against _read
@@ -75,23 +79,32 @@ function from(Readable, iterable, opts) {
   }
 
   async function next() {
-    try {
-      const { value, done } = await iterator.next();
-      if (done) {
-        readable.push(null);
-      } else {
-        const res = await value;
-        if (res === null) {
-          reading = false;
-          throw new ERR_STREAM_NULL_VALUES();
-        } else if (readable.push(res)) {
-          next();
+    for (;;) {
+      try {
+        const { value, done } = isAsync ?
+          await iterator.next() :
+          iterator.next();
+
+        if (done) {
+          readable.push(null);
         } else {
-          reading = false;
+          const res = (value &&
+            typeof value.then === 'function') ?
+            await value :
+            value;
+          if (res === null) {
+            reading = false;
+            throw new ERR_STREAM_NULL_VALUES();
+          } else if (readable.push(res)) {
+            continue;
+          } else {
+            reading = false;
+          }
         }
+      } catch (err) {
+        readable.destroy(err);
       }
-    } catch (err) {
-      readable.destroy(err);
+      break;
     }
   }
   return readable;