stream: implement fetch body mixin on Readable

doc/api/stream.md

@@ -814,6 +814,8 @@ added: v0.9.4
 
 <!--type=class-->
 
+`Readable` implements the body mixin API from the [fetch specification][].
+
 ##### Event: `'close'`
 <!-- YAML
 added: v0.9.4
@@ -986,6 +988,51 @@ added: v0.9.4
 The `'resume'` event is emitted when [`stream.resume()`][stream-resume] is
 called and `readableFlowing` is not `true`.
 
+##### `readable.arrayBuffer()`
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1 - Experimental
+
+* Returns: {Promise}
+
+Returns a promise fulfilled with the full content as an {ArrayBuffer}.
+
+##### `readable.blob()`
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1 - Experimental
+
+* Returns: {Promise}
+
+Returns a promise fulfilled with the full content as a {Blob}.
+
+##### `readable.body`
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1 - Experimental
+
+* Returns: {ReadableStream}
+
+Returns a `ReadableStream`.
+
+##### `readable.bodyUsed`
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1 - Experimental
+
+* Returns: {boolean}
+
+Returns true if stream has emitted `'data'`, `'end'`, `'error'` or
+`'close'`.
+
 ##### `readable.destroy([error])`
 <!-- YAML
 added: v8.0.0
@@ -1040,6 +1087,18 @@ readable.resume();
 readable.isPaused(); // === false
 ```
 
+##### `readable.json()`
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1 - Experimental
+
+* Returns: {Promise}
+
+Returns a promise fulfilled with the full content read as an UTF-8
+string and parsed as a JSON object.
+
 ##### `readable.pause()`
 <!-- YAML
 added: v0.9.4
@@ -1341,6 +1400,17 @@ readable.on('data', (chunk) => {
 });
 ```
 
+##### `readable.text()`
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1 - Experimental
+
+* Returns: {Promise}
+
+Returns a promise fulfilled with the full content read as an UTF-8 string.
+
 ##### `readable.unpipe([destination])`
 <!-- YAML
 added: v0.9.4
@@ -3503,6 +3573,7 @@ contain multi-byte characters.
 [child process stdin]: child_process.md#child_process_subprocess_stdin
 [child process stdout and stderr]: child_process.md#child_process_subprocess_stdout
 [crypto]: crypto.md
+[fetch specification]: https://fetch.spec.whatwg.org/#body-mixin
 [fs read streams]: fs.md#fs_class_fs_readstream
 [fs write streams]: fs.md#fs_class_fs_writestream
 [http-incoming-message]: http.md#http_class_http_incomingmessage