From 0c18c49f0efd8296e7cf73680c8df0674ac4131c Mon Sep 17 00:00:00 2001
From: Matteo Collina <hello@matteocollina.com>
Date: Thu, 12 Dec 2019 14:40:50 +0100
Subject: [PATCH] stream: do not chunk strings and Buffer in Readable.from
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PR-URL: https://github.com/nodejs/node/pull/30912
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Rich Trott <rtrott@gmail.com>
---
 doc/api/stream.md                   |  4 ++++
 lib/internal/streams/from.js        | 12 ++++++++++++
 test/parallel/test-readable-from.js | 13 ++++++++++++-
 3 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/doc/api/stream.md b/doc/api/stream.md
index a880bae5bbe31d..ad13e8ee6ade38 100644
--- a/doc/api/stream.md
+++ b/doc/api/stream.md
@@ -1642,6 +1642,10 @@ readable.on('data', (chunk) => {
 });
 ```
 
+Calling `Readable.from(string)` or `Readable.from(buffer)` will not have
+the strings or buffers be iterated to match the other streams semantics
+for performance reasons.
+
 ## API for Stream Implementers
 
 <!--type=misc-->
diff --git a/lib/internal/streams/from.js b/lib/internal/streams/from.js
index a060638df2dcfe..474db60b8930a2 100644
--- a/lib/internal/streams/from.js
+++ b/lib/internal/streams/from.js
@@ -4,6 +4,7 @@ const {
   Symbol,
   SymbolIterator
 } = primordials;
+const { Buffer } = require('buffer');
 
 const {
   ERR_INVALID_ARG_TYPE
@@ -11,6 +12,17 @@ const {
 
 function from(Readable, iterable, opts) {
   let iterator;
+  if (typeof iterable === 'string' || iterable instanceof Buffer) {
+    return new Readable({
+      objectMode: true,
+      ...opts,
+      read() {
+        this.push(iterable);
+        this.push(null);
+      }
+    });
+  }
+
   if (iterable && iterable[Symbol.asyncIterator])
     iterator = iterable[Symbol.asyncIterator]();
   else if (iterable && iterable[SymbolIterator])
diff --git a/test/parallel/test-readable-from.js b/test/parallel/test-readable-from.js
index e43cec6b1e5246..6cc9216a306378 100644
--- a/test/parallel/test-readable-from.js
+++ b/test/parallel/test-readable-from.js
@@ -56,13 +56,23 @@ async function toReadablePromises() {
 async function toReadableString() {
   const stream = Readable.from('abc');
 
-  const expected = ['a', 'b', 'c'];
+  const expected = ['abc'];
 
   for await (const chunk of stream) {
     strictEqual(chunk, expected.shift());
   }
 }
 
+async function toReadableBuffer() {
+  const stream = Readable.from(Buffer.from('abc'));
+
+  const expected = ['abc'];
+
+  for await (const chunk of stream) {
+    strictEqual(chunk.toString(), expected.shift());
+  }
+}
+
 async function toReadableOnData() {
   async function* generate() {
     yield 'a';
@@ -154,6 +164,7 @@ Promise.all([
   toReadableSyncIterator(),
   toReadablePromises(),
   toReadableString(),
+  toReadableBuffer(),
   toReadableOnData(),
   toReadableOnDataNonObject(),
   destroysTheStreamWhenThrowing(),