stream: do not chunk strings and Buffer in Readable.from

PR-URL: #30912 Reviewed-By: Ruben Bridgewater <[email protected]> Reviewed-By: Michaël Zasso <[email protected]> Reviewed-By: Anna Henningsen <[email protected]> Reviewed-By: Rich Trott <[email protected]>

Author: mcollina

doc/api/stream.md

@@ -1641,6 +1641,10 @@ 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-->

lib/internal/streams/from.js

@@ -4,13 +4,25 @@ const{
  SymbolAsyncIterator,
  SymbolIterator
 }=primordials;
+const{ Buffer }=require('buffer');
 
 const{
 ERR_INVALID_ARG_TYPE
 }=require('internal/errors').codes;
 
 functionfrom(Readable,iterable,opts){
 letiterator;
+if(typeofiterable==='string'||iterableinstanceofBuffer){
+returnnewReadable({
+objectMode: true,
+ ...opts,
+read(){
+this.push(iterable);
+this.push(null);
+}
+});
+}
+
 if(iterable&&iterable[SymbolAsyncIterator])
 iterator=iterable[SymbolAsyncIterator]();
 elseif(iterable&&iterable[SymbolIterator])

test/parallel/test-readable-from.js

@@ -56,13 +56,23 @@ async function toReadablePromises(){
 asyncfunctiontoReadableString(){
 conststream=Readable.from('abc');
 
-constexpected=['a','b','c'];
+constexpected=['abc'];
 
 forawait(constchunkofstream){
 strictEqual(chunk,expected.shift());
 }
 }
 
+asyncfunctiontoReadableBuffer(){
+conststream=Readable.from(Buffer.from('abc'));
+
+constexpected=['abc'];
+
+forawait(constchunkofstream){
+strictEqual(chunk.toString(),expected.shift());
+}
+}
+
 asyncfunctiontoReadableOnData(){
 asyncfunction*generate(){
 yield'a';
@@ -154,6 +164,7 @@ Promise.all([
 toReadableSyncIterator(),
 toReadablePromises(),
 toReadableString(),
+toReadableBuffer(),
 toReadableOnData(),
 toReadableOnDataNonObject(),
 destroysTheStreamWhenThrowing(),