buffer: implement blob.textStream()

Signed-off-by: Matthew Aitken <maitken033380023@gmail.com>
PR-URL: #64036
Refs: w3c/FileAPI@cd1d1da
Refs: nodejs/undici@0d6ecc5
Reviewed-By: René <contact.9a5d6388@renegade334.me.uk>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Gürgün Dayıoğlu <hey@gurgun.day>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Mattias Buelens <mattias@buelens.com>

Author: KhafraDev

doc/api/buffer.md

@@ -593,6 +593,18 @@ added:
 Returns a promise that fulfills with the contents of the `Blob` decoded as a
 UTF-8 string.
 
+### `blob.textStream()`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+* Returns: {ReadableStream}
+
+Returns a new `ReadableStream` that allows the content of the `Blob` to be read
+as a stream of UTF-8 decoded strings. It is equivalent to piping
+[`blob.stream()`][] through a [`TextDecoderStream`][] set up with UTF-8.
+
 ### `blob.type`
 
 <!-- YAML
@@ -5610,10 +5622,12 @@ introducing security vulnerabilities into an application.
 [`String.prototype.indexOf()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/indexOf
 [`String.prototype.lastIndexOf()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/lastIndexOf
 [`String.prototype.length`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/length
+[`TextDecoderStream`]: webstreams.md#class-textdecoderstream
 [`TypedArray.from()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray/from
 [`TypedArray.prototype.set()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray/set
 [`TypedArray.prototype.slice()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray/slice
 [`TypedArray.prototype.subarray()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray/subarray
+[`blob.stream()`]: #blobstream
 [`buf.buffer`]: #bufbuffer
 [`buf.compare()`]: #bufcomparetarget-targetstart-targetend-sourcestart-sourceend
 [`buf.entries()`]: #bufentries

lib/internal/blob.js

@@ -85,6 +85,7 @@ const kNotCloneable = Symbol('kNotCloneable');
 constdisallowedTypeCharacters=/[^\u{0020}-\u{007E}]/u;
 
 letReadableStream;
+letTextDecoderStream;
 
 constenc=newTextEncoder();
 letdec;
@@ -100,6 +101,13 @@ function lazyReadableStream(options) {
 returnnewReadableStream(options);
 }
 
+functionlazyTextDecoderStream(){
+// eslint-disable-next-line no-global-assign
+TextDecoderStream??=
+require('internal/webstreams/encoding').TextDecoderStream;
+returnnewTextDecoderStream();
+}
+
 const{EOL}=require('internal/constants');
 
 functionisBlob(object){
@@ -325,6 +333,17 @@ class Blob {
 thrownewERR_INVALID_THIS('Blob');
 returncreateBlobReaderStream(this[kHandle].getReader());
 }
+
+/**
+ * @returns {ReadableStream}
+ */
+textStream(){
+if(!isBlob(this))
+thrownewERR_INVALID_THIS('Blob');
+conststream=createBlobReaderStream(this[kHandle].getReader());
+constdecoder=lazyTextDecoderStream();
+returnstream.pipeThrough(decoder);
+}
 }
 
 functionTransferableBlob(handle,length,type=''){
@@ -358,6 +377,7 @@ ObjectDefineProperties(Blob.prototype, {
 type: kEnumerableProperty,
 slice: kEnumerableProperty,
 stream: kEnumerableProperty,
+textStream: kEnumerableProperty,
 text: kEnumerableProperty,
 arrayBuffer: kEnumerableProperty,
 bytes: kEnumerableProperty,

test/parallel/test-blob.js

@@ -3,7 +3,7 @@
 
 constcommon=require('../common');
 constassert=require('assert');
-const{ Blob }=require('buffer');
+const{ Blob, File}=require('buffer');
 const{ inspect }=require('util');
 const{EOL}=require('os');
 const{ kState }=require('internal/webstreams/util');
@@ -524,3 +524,22 @@ assert.throws(() => new Blob({}), {
 Blob.prototype.arrayBuffer=arrayBuffer;
 }
 })().then(common.mustCall());
+
+{
+assert.strictEqual(typeofBlob.prototype.textStream,'function');
+assert.strictEqual(typeofFile.prototype.textStream,'function');
+assert.strictEqual(File.prototype.textStream,Blob.prototype.textStream);
+}
+
+(async()=>{
+constsmiley=Buffer.from('😀','utf8');
+constblob=newBlob(['hello ',smiley.subarray(0,2),smiley.subarray(2)]);
+conststream=blob.textStream();
+assert.ok(streaminstanceofReadableStream);
+letresult='';
+forawait(constchunkofstream){
+assert.strictEqual(typeofchunk,'string');
+result+=chunk;
+}
+assert.strictEqual(result,'hello 😀');
+})().then(common.mustCall());