util: implement WHATWG Encoding Standard API

Provide an (initially experimental) implementation of the WHATWG Encoding
Standard API (`TextDecoder` and `TextEncoder`). The is the same API
implemented on the browser side.

By default, with small-icu, only the UTF-8, UTF-16le and UTF-16be decoders
are supported. With full-icu enabled, every encoding other than iso-8859-16
is supported.

This provides a basic test, but does not include the full web platform
tests. Note: many of the web platform tests for this would fail by default
because we ship with small-icu by default.

A process warning will be emitted on first use to indicate that the
API is still experimental. No runtime flag is required to use the
feature.

Refs: https://encoding.spec.whatwg.org/
PR-URL: #13644
Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

doc/api/buffer.md

@@ -193,11 +193,12 @@ The character encodings currently supported by Node.js include:
 
 * `'hex'` - Encode each byte as two hexadecimal characters.
 
-*Note*: Today's browsers follow the [WHATWG spec] which aliases both 'latin1'
-and ISO-8859-1 to win-1252. This means that while doing something like
-`http.get()`, if the returned charset is one of those listed in the WHATWG spec
-it's possible that the server actually returned win-1252-encoded data, and
-using `'latin1'` encoding may incorrectly decode the characters.
+*Note*: Today's browsers follow the [WHATWG Encoding Standard][] which aliases
+both 'latin1' and ISO-8859-1 to win-1252. This means that while doing something
+like `http.get()`, if the returned charset is one of those listed in the WHATWG
+specification it is possible that the server actually returned
+win-1252-encoded data, and using `'latin1'` encoding may incorrectly decode the
+characters.
 
 ## Buffers and TypedArray
 <!-- YAML
@@ -2662,7 +2663,6 @@ buf.fill(0);
 console.log(buf);
 ```
 
-
 ## Buffer Constants
 <!-- YAML
 added: 8.2.0
@@ -2730,5 +2730,5 @@ This value may depend on the JS engine that is being used.
 [`util.inspect()`]: util.html#util_util_inspect_object_options
 [RFC1345]: https://tools.ietf.org/html/rfc1345
 [RFC4648, Section 5]: https://tools.ietf.org/html/rfc4648#section-5
-[WHATWG spec]: https://encoding.spec.whatwg.org/
+[WHATWG Encoding Standard]: https://encoding.spec.whatwg.org/
 [iterator]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols

doc/api/util.md

@@ -536,6 +536,156 @@ added: v8.0.0
 A Symbol that can be used to declare custom promisified variants of functions,
 see [Custom promisified functions][].
 
+### Class: util.TextDecoder
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1 - Experimental
+
+An implementation of the [WHATWG Encoding Standard][] `TextDecoder` API.
+
+```js
+const decoder = new TextDecoder('shift_jis');
+let string = '';
+let buffer;
+while (buffer = getNextChunkSomehow()) {
+  string += decoder.decode(buffer, { stream: true });
+}
+string += decoder.decode(); // end-of-stream
+```
+
+#### WHATWG Supported Encodings
+
+Per the [WHATWG Encoding Standard][], the encodings supported by the
+`TextDecoder` API are outlined in the tables below. For each encoding,
+one or more aliases may be used. Support for some encodings is enabled
+only when Node.js is using the full ICU data.
+
+##### Encodings Supported By Default
+
+| Encoding    | Aliases                           |
+| ----------- | --------------------------------- |
+| `'utf8'`    | `'unicode-1-1-utf-8'`, `'utf-8'`  |
+| `'utf-16be'`|                                   |
+| `'utf-16le'`| `'utf-16'`                        |
+
+##### Encodings Requiring Full-ICU
+
+| Encoding          | Aliases                          |
+| ----------------- | -------------------------------- |
+| `'ibm866'`        | `'866'`, `'cp866'`, `'csibm866'` |
+| `'iso-8859-2'`    | `'csisolatin2'`, `'iso-ir-101'`, `'iso8859-2'`, `'iso88592'`, `'iso_8859-2'`, `'iso_8859-2:1987'`, `'l2'`, `'latin2'` |
+| `'iso-8859-3'`    | `'csisolatin3'`, `'iso-ir-109'`, `'iso8859-3'`, `'iso88593'`, `'iso_8859-3'`, `'iso_8859-3:1988'`, `'l3'`, `'latin3'` |
+| `'iso-8859-4'`    | `'csisolatin4'`, `'iso-ir-110'`, `'iso8859-4'`, `'iso88594'`, `'iso_8859-4'`, `'iso_8859-4:1988'`, `'l4'`, `'latin4'` |
+| `'iso-8859-5'`    | `'csisolatincyrillic'`, `'cyrillic'`, `'iso-ir-144'`, `'iso8859-5'`, `'iso88595'`, `'iso_8859-5'`, `'iso_8859-5:1988'`|
+| `'iso-8859-6'`    | `'arabic'`, `'asmo-708'`, `'csiso88596e'`, `'csiso88596i'`, `'csisolatinarabic'`, `'ecma-114'`, `'iso-8859-6-e'`, `'iso-8859-6-i'`, `'iso-ir-127'`, `'iso8859-6'`, `'iso88596'`, `'iso_8859-6'`, `'iso_8859-6:1987'` |
+| `'iso-8859-7'`    | `'csisolatingreek'`, `'ecma-118'`, `'elot_928'`, `'greek'`, `'greek8'`, `'iso-ir-126'`, `'iso8859-7'`, `'iso88597'`, `'iso_8859-7'`, `'iso_8859-7:1987'`, `'sun_eu_greek'` |
+| `'iso-8859-8'`    | `'csiso88598e'`, `'csisolatinhebrew'`, `'hebrew'`, `'iso-8859-8-e'`, `'iso-ir-138'`, `'iso8859-8'`, `'iso88598'`, `'iso_8859-8'`, `'iso_8859-8:1988'`, `'visual'` |
+| `'iso-8859-8-i'`  | `'csiso88598i'`, `'logical'` |
+| `'iso-8859-10'`   | `'csisolatin6'`, `'iso-ir-157'`, `'iso8859-10'`, `'iso885910'`, `'l6'`, `'latin6'` |
+| `'iso-8859-13'`   | `'iso8859-13'`, `'iso885913'` |
+| `'iso-8859-14'`   | `'iso8859-14'`, `'iso885914'` |
+| `'iso-8859-15'`   | `'csisolatin9'`, `'iso8859-15'`, `'iso885915'`, `'iso_8859-15'`, `'l9'` |
+| `'koi8-r'`        | `'cskoi8r'`, `'koi'`, `'koi8'`, `'koi8_r'` |
+| `'koi8-u'`        | `'koi8-ru'` |
+| `'macintosh'`     | `'csmacintosh'`, `'mac'`, `'x-mac-roman'` |
+| `'windows-874'`   | `'dos-874'`, `'iso-8859-11'`, `'iso8859-11'`, `'iso885911'`, `'tis-620'` |
+| `'windows-1250'`  | `'cp1250'`, `'x-cp1250'` |
+| `'windows-1251'`  | `'cp1251'`, `'x-cp1251'` |
+| `'windows-1252'`  | `'ansi_x3.4-1968'`, `'ascii'`, `'cp1252'`, `'cp819'`, `'csisolatin1'`, `'ibm819'`, `'iso-8859-1'`, `'iso-ir-100'`, `'iso8859-1'`, `'iso88591'`, `'iso_8859-1'`, `'iso_8859-1:1987'`, `'l1'`, `'latin1'`, `'us-ascii'`, `'x-cp1252'` |
+| `'windows-1253'`  | `'cp1253'`, `'x-cp1253'` |
+| `'windows-1254'`  | `'cp1254'`, `'csisolatin5'`, `'iso-8859-9'`, `'iso-ir-148'`, `'iso8859-9'`, `'iso88599'`, `'iso_8859-9'`, `'iso_8859-9:1989'`, `'l5'`, `'latin5'`, `'x-cp1254'` |
+| `'windows-1255'`  | `'cp1255'`, `'x-cp1255'` |
+| `'windows-1256'`  | `'cp1256'`, `'x-cp1256'` |
+| `'windows-1257'`  | `'cp1257'`, `'x-cp1257'` |
+| `'windows-1258'`  | `'cp1258'`, `'x-cp1258'` |
+| `'x-mac-cyrillic'`| `'x-mac-ukrainian'` |
+| `'gbk'`           | `'chinese'`, `'csgb2312'`, `'csiso58gb231280'`, `'gb2312'`, `'gb_2312'`, `'gb_2312-80'`, `'iso-ir-58'`, `'x-gbk'` |
+| `'gb18030'`       | |
+| `'big5'`          | `'big5-hkscs'`, `'cn-big5'`, `'csbig5'`, `'x-x-big5'` |
+| `'euc-jp'`        | `'cseucpkdfmtjapanese'`, `'x-euc-jp'` |
+| `'iso-2022-jp'`   | `'csiso2022jp'` |
+| `'shift_jis'`     | `'csshiftjis'`, `'ms932'`, `'ms_kanji'`, `'shift-jis'`, `'sjis'`, `'windows-31j'`, `'x-sjis'` |
+| `'euc-kr'`        | `'cseuckr'`, `'csksc56011987'`, `'iso-ir-149'`, `'korean'`, `'ks_c_5601-1987'`, `'ks_c_5601-1989'`, `'ksc5601'`, `'ksc_5601'`, `'windows-949'` |
+
+*Note*: The `'iso-8859-16'` encoding listed in the [WHATWG Encoding Standard][]
+is not supported.
+
+#### new TextDecoder([encoding[, options]])
+
+* `encoding` {string} Identifies the `encoding` that this `TextDecoder` instance
+  supports. Defaults to `'utf-8'`.
+* `options` {Object}
+  * `fatal` {boolean} `true` if decoding failures are fatal. Defaults to
+    `false`.
+  * `ignoreBOM` {boolean} When `true`, the `TextDecoder` will include the byte
+     order mark in the decoded result. When `false`, the byte order mark will
+     be removed from the output. This option is only used when `encoding` is
+     `'utf-8'`, `'utf-16be'` or `'utf-16le'`. Defaults to `false`.
+
+Creates an new `TextDecoder` instance. The `encoding` may specify one of the
+supported encodings or an alias.
+
+#### textDecoder.decode([input[, options]])
+
+* `input` {ArrayBuffer|DataView|TypedArray} An `ArrayBuffer`, `DataView` or
+  Typed Array instance containing the encoded data.
+* `options` {Object}
+  * `stream` {boolean} `true` if additional chunks of data are expected.
+    Defaults to `false`.
+* Returns: {string}
+
+Decodes the `input` and returns a string. If `options.stream` is `true`, any
+incomplete byte sequences occuring at the end of the `input` are buffered
+internally and emitted after the next call to `textDecoder.decode()`.
+
+If `textDecoder.fatal` is `true`, decoding errors that occur will result in a
+`TypeError` being thrown.
+
+#### textDecoder.encoding
+
+* Value: {string}
+
+The encoding supported by the `TextDecoder` instance.
+
+#### textDecoder.fatal
+
+* Value: {boolean}
+
+The value will be `true` if decoding errors result in a `TypeError` being
+thrown.
+
+#### textDecoder.ignoreBOM
+
+* Value: {boolean}
+
+The value will be `true` if the decoding result will include the byte order
+mark.
+
+### Class: util.TextEncoder
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1 - Experimental
+
+An implementation of the [WHATWG Encoding Standard][] `TextEncoder` API. All
+instances of `TextEncoder` only support `UTF-8` encoding.
+
+```js
+const encoder = new TextEncoder();
+const uint8array = encoder.encode('this is some data');
+```
+
+#### textEncoder.encode([input])
+
+* `input` {string} The text to encode. Defaults to an empty string.
+* Returns: {Uint8Array}
+
+UTF-8 Encodes the `input` string and returns a `Uint8Array` containing the
+encoded bytes.
+
 ## Deprecated APIs
 
 The following APIs have been deprecated and should no longer be used. Existing
@@ -1022,3 +1172,4 @@ Deprecated predecessor of `console.log`.
 [Custom promisified functions]: #util_custom_promisified_functions
 [constructor]: https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Object/constructor
 [semantically incompatible]: https://github.com/nodejs/node/issues/4179
+[WHATWG Encoding Standard]: https://encoding.spec.whatwg.org/